R&D for Arms ControlFrancis Poda, Savannah River Technology Center George L. Cajigal, Threat Reduction Support Center Production Ofﬁce Arms Control and Nonproliferation Technologies

TechnologyR&D for Arms

Control

TechnologyR&D for Arms

Control

Arms Control and Nonproliferation TechnologiesOffice of Nonproliferation Research and Engineering Spring 2001

Uranium

Uranium

Plutonium

Plutonium Plutonium

Uranium

Plutonium

Uranium

Reprocessing

Uraniummining

Uraniumprocessing

Highly EnrichedUranium

HEU weaponscomponent

Military use

Military use

Pre-1997

Post

-199

7, n

aval

fue

l, co

mm

erci

al

Pre-

1997

, wea

po

ns-

gra

de

Weapons stockpile

De-Matedwarheadstorage

Assembly

Civilian reactors

Plutonium productionreactors

Partsfabrication

Enrichment

High-levelwaste

storage

Pu wasteimmobilization

Navalreactor

rods

PuStrategic Reserve

Pu componentdisassembly and

conversionPu weaponscomponent

Cooperative Threat Reduction (CTR)

HEU Transparency

Material Protection, Control, and Accounting (MPC&A)

Mayak Transparency

Plutonium Production Reactor Agreement (PPRA)

U.S.–Russian Plutonium Disposition Agreement

Trilateral Initiative

Disassembly

Reprocessing

Mixed-oxidefuel production

HEU componentdisassembly and

conversion

Processing/downblending

Pu conversion and blending

HEUStrategic Reserve

Material

Storage

Warheadstorage/staging

Civilian reactors

Civilian reactors

StrategicReserve

Storage

StrategicReserve

Storage

excess

Storage

Uraniumfuel rods

Spentfuel

LEU

Naturaluranium

Spent

Naturalor LEU

Navalfuel

storage

Fuelfabrication

Fuelfabrication

Pu partsfabrication

Fuelfabrication

excess

Storage

Storage DispositionWeapons

DisassemblyWeaponsAssembly

MaterialsProduction

WeaponsStockpile

See reverse side for an explanation of this chart For an electronic copy of this file, contact the ACNT Production Office at Lawrence Livermore National Laboratory.

FACILITIES and INSTRUMENTATION• 21,000 sq. feet of laboratory space

• 0.5–25 MeV electron LinacShort-pulse mode: pulse widths: 30–50 ps, 10 nC/pulse, 0.5% beam energy spread-Long-pulse mode: pulse width: 4 µs, 2,000 nC/pulse-Repetition rate: single shot to 240 Hz-Three beam ports

• Two 4-MeV Linacs-Field radiography/neutron source capability

• Varitron Accelerator (Varian Associates Inc.)-2–12-MeV energy range-Pulsewidths: 500 ns to 4 µs Beam energy and current analysis-Capable of up to3000 R/min (@ 1 m)

• 18-MeV Linac (Varian Associates, Inc.)– Beam energy and current analysis– Pulse widths: 15 ns to 2 µs

• Two positive ion Van de Graaffs-High-Voltage Engineering, Inc.-2-MV potential

• Tandetron-High-Voltage Engineering, Inc. 1.5 MeV/amu

• D/T Neutron Generator-Sodern Genie 16

• Supporting Instrumentation-Calibrated 20-GHz sampling scope-Multi-parameterdata acquisition system-Calibrated PIN diodes-Internet 11 connection

• Fixed facility and field digital radiography and computed tomography systemsusing x-ray generators from 30–450 kV

SERVICES• Wide range of accelerator types available to researchers

• Customized user support

• Photon, electron, and neutron transport calculations for system applications

• Photon and neutron dosimetry

• Customized radiation detection system development

• Experimental verification of predictions and objectives

• Customized accelerator performance and modifications

• Single point-of-contact: simplified coordination between researchersexperimental needs and applicable resources.

CONTACTS

Dr. Frank HarmonDirectorIdaho State UniversityCampus Box 8263Pocatello, Idaho 83209Phone: 208.282.5877Fax: 208.282.5878Email: [email protected]

Dr. James L. JonesAssociate DirectorIdaho National Engineering andEnvironmental Laboratory (INEEL)PO Box 1625Idaho Falls, Idaho 83415-2802Phone: 208.526.1730Fax: 208.526.5208Email: [email protected]

Dr. Jay KunzeAssociate DirectorIdaho State UniversityCampus Box 8060Pocatello, Idaho 83209Phone: 208.282.2902Fax: 208.282.4538Email: [email protected]

Idaho Accelerator Center1500 Alvin Ricken DrivePocatello, Idaho 83209

www.iac.isu.edu

NN-50’s Materials Protection, Control, and Accounting (MPC&A) program focuses on enhanc-ing the physical protection and material-accountancy infrastructure at former Soviet Union sitescontaining weapons-usable nuclear material. This work is augmented by the program’s involve-ment with enhancements to the regulatory framework within Russia, national-level materialaccounting, nuclear-material transportation, as well as other related activities. The program’s goalis to reduce the risk to U.S. national security of an undetected theft of weapons-usable materialfrom the former Soviet sites by enhancing their MPC&A capabilities. The placement of a yellowbox around a given type of facility on the diagram signifies that the program is involved, or isplanning to be involved, in infrastructure upgrades at these sites.

The Idaho Accelerator Center (IAC), located at Idaho State University, hasoperated since 1994 in partnership with the Idaho National Engineering andEnvironmental Laboratory and the Department of Energy

RESEARCHConducting fundamental and applied research in low-energy nuclearscience using accelerator-produced radiation

IAC provides university, government, and industrial scientists and engineersunparalleled research opportunities: Radiography, tomography, and nucleartechniques for nondestructive evaluation and nondestructive assay; industrialand agricultural applications of accelerator-produced radiation; ion and photon-beam analysis for environmental and mineral extraction needs; radiation sciencein medicine; radioisotope production; accelerator-based neutron therapy; radia-tion effects testing for semiconductor devices; instrument and radiation-detectortesting for weapons surety studies and fundamental nuclear physics research.

EDUCATIONOffering undergraduate and graduate degrees in physics, healthphysics, engineering, and applied science

IAC supports educational activities at all levels of Idaho State University’s aca-demic areas, including physics, health physics, engineering, waste management,geology, biological sciences, and health sciences. The University offers bachelor’sand master’s degrees in physics and health physics, and in cooperation with theCollege of Engineering, doctorates in engineering and applied science. Studentsparticipate in all IAC research and development. The research staff has publishedmore than 100 peer-reviewed publications over the past five years.

PARTNERSHIPS AND COLLABORATIONSTeaming with university government and commercial partners onapplied research, testing and technology deployment.

IAC offers technical expertise and state-of-the-art facilities for collaborationswith universities, government agencies, and commercial and industrial organi-zations. These partnerships promote practical advances in nuclear and radiationscience and facilitate the transfer of technology to the private sector. IAC collab-orations range from agricultural applications of accelerator-produced radiationto nondestructive examination through gamma-ray spectroscopy, radiography,and tomography. IAC partners conduct research and testing on applications inenvironmental remediation, waste management, chemical-weapons verifica-tion, contraband detection, and radiation effects.

Accelerator Applications andRadiation Science

ACNT • Technology R&D for Arms Control • Spring 2001

The purpose of ArmsControl and Nonproliferation

Technologies is to enhance communicationbetween the technologists in the NNSAcommunity who develop means to verifycompliance with agreements and thepolicymakers who negotiate agreements.

Published byU.S. Department of EnergyNational Nuclear Security Administration Defense Nuclear Nonproliferation ProgramsKenneth Baker, Acting Director

DOE/ACNT Project ManagerRobert WaldronOffice of Nonproliferation Research and Engineering

Issue EditorDavid Spears

Scientific EditorArden Dougan

Managing EditorGorgiana M. Alonzo

Art/Copyediting/Design/LayoutJohn DanielsonDwight JenningsSylvia McDanielKelly Spruiell

ReviewersThomas GosnellJames MorganRobert ScarlettJames Woodard

Editorial AssistanceCatherine Anderson, Los Alamos National LaboratoryFrancis Poda, Savannah River Technology CenterGeorge L. Cajigal, Threat Reduction Support Center

Production OfficeArms Control and Nonproliferation TechnologiesLawrence Livermore National Laboratory7000 East Ave. (L-185)Livermore, CA 94550

CorrespondenceGorgiana M. AlonzoPhone 925.424.6100Fax 925.423.9091E-mail [email protected]

Disclaimer:Reproduction of this document requires the written consentof the originator, his/her successor, or higher authority. Thisreport was prepared as an account of work sponsored bythe United States Government. Neither the United StatesGovernment nor the United States Department of Energynor any of their employees makes any warranty, express orimplied, or assumes any legal liability or responsibility forthe accuracy, completeness, or usefulness of any information,apparatus, product, or process disclosed, or represents thatits use would not infringe privately owned rights. Referenceherein to any specific commercial product, process, or serviceby trade name, trademark, manufacturer, or otherwise, doesnot necessarily constitute or imply its endorsement, recom-mendation, or favoring by the United States Government.The views and opinions of authors expressed herein donot necessarily state or reflect those of the United StatesGovernment and shall not be used for advertising orproduct endorsement purposes.

Focus on TransparencyArms control treaties and agreements directlyinfluence the national security of the UnitedStates. Security decisions made today are basedon that influence. Strategic Arms ReductionTreaty (START) I began a reduction of nuclearweapons. Fortunately, START I is easily verifiedusing straightforward methods—literally tapemeasures and plumb bobs coupled withNational Technical Means and direct observa-tion. As we enter into new negotiations, there isa desire to expand the traditional approach byfocusing on the warheads themselves ratherthan on their delivery systems. More moderntreaties, involving both nuclear warheads anddelivery vehicles, are not as simple to verify.Within the last few years, and in the foreseeablefuture, emphasis has increased on “transparen-cy measures” that will open “windows” on thenuclear-weapons activities of the signatories tosuch agreements—including the U.S. Thesetransparency measures cannot be verified in thestrict START I sense, but all of the proposed ini-tiatives are based on high-technology measure-ments to provide the necessary windows.

We define transparency as measures andprocedures that increase our confidence in anegotiated activity taking place as required.Verification, then, is defined as measurementsand procedures that prove a negotiated activityis taking place.

To support research and development (R&D)in this area, the Departments of Energy andDefense developed the Joint IntegratedTechnology Implementation Plan. Technicalexperts from both communities contribute tothe “Integrated” Plan, supporting R&D in armscontrol and maximizing the research dollar byavoiding duplication of effort.

Contact: David SpearsNNSA/Office of Nonproliferation Research and EngineeringPhone: 202.586.1313Fax: 202.586.2612Email: [email protected]

ACNT • Technology R&D for Arms Control • Spring 2001 1

ContentsTransparency and VerificationTransparency and Verification Issues Associated with Arms Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2Verification Methods: Attributes vs. Templates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4Information Barriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6Certification and Authentication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7Treaties, Agreements, and Initiatives Strategic Arms Reduction Treaties (START): I and II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8The INF Treaty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9The MRI Agreement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9Transparency Measures for the U.S.–Russia HEU Purchase Agreement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10Converting Weapons-Grade HEU (90% enriched) to LEU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11Mayak Transparency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12Fissile Material Cut-off Treaty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13Fissile Material Transparency Technology Demonstration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14Attribute Measurement System with Information Barrier Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15The Trilateral Initiative: Attributes Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16U.S.–Russia Plutonium Production Reactor Agreement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18A Core-Discharge Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19Future Arms Reduction Initiatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20The Comprehensive Test Ban Treaty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21Facilities The Pantex Plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22Savannah River Site’s K Area Material Storage Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23TA-18 at Los Alamos National Laboratory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24The Radiation Measurement Facility at Lawrence Livermore National Laboratory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26Overview to Arms Control Technology About the Atomic Nucleus, Radioactivity, Fissile Materials, and Transparency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28Plutonium Using Low-Resolution, Gamma-Ray Spectroscopy To Detect the Presence of Plutonium . . . . . . . . . . . . . . . . . . . . . . . . .30Measuring Plutonium Isotopes and Age with MGA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31Pu300, Pu600, and Pu900 Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32Absence of Oxide—Neutron Multiplicity Counting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35Estimating Plutonium Mass via Singles Neutron Counting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36Measuring Plutonium Mass by Neutron Multiplicity Counting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37Minimum-Mass Estimates of Plutonium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38Symmetry Measurements of Plutonium Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40Gamma-Ray Imaging To Determine Plutonium Shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42Autoradiography Adaptation Using Optically Stimulated Luminescence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43Attributes and Templates from Active Measurements with NMIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44Uranium Determining the Presence of HEU with Passive Detection Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46Active Interrogation for Monitoring HEU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48Blend-Down Monitoring System for HEU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50Blend-Down Enrichment Monitor for HEU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51Portable Equipment for Uranium Enrichment Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52Determining Uranium Enrichment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53Chain-of-Custody Chain-of-Custody Monitoring of Warhead Dismantlement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54Fission-Product Tagging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56Nondestructive Assay of Special Nuclear Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57Alternative Signatures Identifying Weapon Components in Sealed Containers by Electromagnetic Induction . . . . . . . . . . . . . . . . . . . . . . . . . .58Thermal Infrared Signatures of Containers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60Tags and Seals Tags and Seals for a Potential Strategic Arms Control Monitoring Regime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62Seals for Transparency and Treaty Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64Detection of Nonnuclear ComponentsChemical-Explosive Detection by Neutron Interrogation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .66Points of Contact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .68

Transparency and Verification

U.S. and Russian experts engagein joint experiments for thedetermination of appropriateplutonium attributes and mea-surement methods for the MRIAgreement (1996).

The overarching problem for a largenumber of current transparency activi-ties—the Highly Enriched Uranium

(HEU) Purchase Agreement, the TrilateralInitiative, the Plutonium ProductionReactor Agreement (PPRA), and MayakTransparency—revolves around identifyingthe material in a closed container as either awarhead, a weapon component, or fissilematerial from a dismantled nuclear weapon.

Further complicating the problem is thatsome or all of the information concerningthe material in the container is consideredclassified by at least one party to the agree-

ment. Two solutions to this problem havebeen proposed: template-matching andattribute measurements (see page 4). Mostof the current negotiations seem to be head-ed toward the attribute approach because itdoes not require the retention of classifieddata obtained during an inspection mea-surement. However, the Russians haverecently proposed some novel applicationsof template-matching that invite furtherstudy.

The attribute approach to transparencymeasurements involves determining a smallnumber of measurable quantities character-istic of the object under inspection—be itwarhead, component, or fissile material.These attributes are determined from firstprinciples as being a necessary element ofthat object. Possible attributes mightinclude—• the presence of radiation• the presence of plutonium• the presence of weapons-grade plutonium• plutonium mass• uranium enrichment level.

Along with the determination of theattribute itself, a threshold value for thatattribute must be established that separatesacceptable and unacceptable material.Although most of the attributes being con-sidered at the present involve radiationmeasurements, this is not the onlyapproach. Attributes such as acoustic signa-tures, chemical emanations, and eddy-cur-rent effects have been considered in thepast and may yet prove fruitful in some sit-uations.

The history of attribute measurements canbe traced back at least to the START I negoti-ations. The attribute of interest then was theneutron radiation, or lack thereof, emanatingfrom containers of a certain size found in aweapons storage area. In this case, theattribute contained no classified information.The attribute measurement technique reallycame to the forefront with the JointStatement on Mutual Reciprocal Inspections(MRIs). Following the signing of this agree-ment, weapons experts from both sides metfor three week-long sessions in Moscow todetermine the attributes characteristic ofmaterial removed from a dismantled nuclearweapon. It was finally agreed that the usefulattributes for this agreement were—• presence of weapons-grade plutonium• mass above a certain threshold• shape of the object in the container.

2 ACNT • Technology R&D for Arms Control • Spring 2001

Transparency and Verification IssuesAssociated with Arms Control


Because the signing of an Agreement forCooperation with the Russians (whichwould have allowed the exchange of classi-fied information for arms control purposes)seemed imminent, the issue of the classifiednature of some of the attributes wasignored. Although the actual MRI agree-ment eventually foundered on the shoals ofthe classification issue, the procedure devel-oped for determining the useful attributeshas persisted to the current era.

The nature of the specific agreementdetermines the complexity of the attributeset appropriate for that negotiation. Thesecan run from the very simple for the HEUPurchase and PPRA to the highly complexfor Mayak Transparency negotiations. Forthe HEU Purchase, essentially one attributeis important, namely the uranium enrich-ment prior to the blenddown of materialremoved from dismantled nuclear weapons.For the PPRA, the interesting attributes arethe presence of weapons-grade plutoniumand the time (age) since chemical purifica-tion of the plutonium in the container. Onthe other hand, for the Mayak agreement,the attribute set is highly complex, drivenby the need to develop confidence that thematerial, possibly in an unclassified shape,is derived from dismantled nuclearweapons.

The linchpin that makes the attributemethod attractive for modern negotiationshas been the information barrier concept(see page 6). As noted, one side or the otherconsiders the values of some or all of therelevant attributes to be classified from itssecurity point of view. With the collapse ofthe negotiations on an Agreement forCooperation in 1996, it appeared thatattribute methods would no longer be use-ful. However, with the development—andRussian acceptance—of the informationbarrier concept within the context of the

Trilateral Initiative negotiations, attributetechniques were given a new importance.In these techniques, the measured value ofa given attribute is compared to an agreed,unclassified threshold. The system thenreports whether or not the measurementfalls above or below the threshold value asa pass/fail (“red light/green light”). Withthe development of attribute measurementsystems that encompass the informationbarrier idea, the future for attribute tech-niques in arms control agreements seemsassured.

James MorganLawrence Livermore National Laboratory

U.S. and Russian experts discussa shape measurement of anitem inside a Russian storagecontainer for special nuclearmaterials.


Transparency:Measurementsand procedureswhich increaseconfidence that anegotiated activityis taking place asrequired.

Verification:Measurementsand proceduresthat prove anegotiated activityis taking place asrequired.

Two fundamentally different approachescan provide confidence that declara-tions concerning items in a nuclear-

weapon arms control regime are true. Theattribute approach is based on the intrinsiccharacteristics of nuclear weapons and theircomponents. The template approach com-pares the radiation signature from an inspect-ed item with a known standard for a weaponor component of the same type. Bothapproaches—the centerpiece of technologyR&D for several years—have been investigat-ed in parallel with the treaty negotiations.

Attribute methods increase confidence inthe authenticity of an inspected item bydemonstrating that the item possesses thecharacteristics of a nuclear weapon.Although several characteristics might beconsidered, two are illustrative: (1) the massof plutonium must exceed a specified thresh-old and (2) the ratio of 240Pu to 239Pu mustbe less than a declared maximum. Thoughclassified data are collected to confirm thesetwo attributes, it is not necessary to storeclassified information because the attributesthemselves are unclassified. A key feature ofthe atribute approach is the ability toauthenticate the measurement system usingan unclassified standard.

The template approach identifies an itemby comparing a measurement with anempirical template for the declared item. Ifthe item is classified, then the template isalso classified and is never viewed byinspectors. This requires an automated pro-cedure to certify that the measurementagrees with the template within specifieduncertainty limits. Template comparisonsalso require secure storage and certificationof a classified database, but no a prioriassumptions are made regarding the charac-teristics of the inspected item. An issuewith the template approach is the need fora “trusted” item of each weapon and com-ponent type to use as template sources.

The arms control treaty dictates whichverification method is most appropriate.Procedures associated with attribute mea-surements are simpler because a classifieddatabase is not required. There is also adegree of comfort in knowing that eachinspected item exhibits a clearly defined setof characteristics. In contrast, templatecomparisons rely on the abstraction that anitem is essentially the same as one measuredpreviously. Template comparisons are theonly practical solution if the objective isdemonstrating that two or more weapons orcomponents are of the same type.Depending on the requirements, eithermethod or a combination of the two mightbe used.

Attribute ApproachSeveral attribute-measurement methods

use both passive and active (where theinspected item is irradiated by an externalradiation source) techniques. The TrustedRadiation Attribute Demonstration System(TRADS) is an example of a passive system.The only detector required to confirm theattributes of weapons-grade plutonium andhighly enriched uranium (HEU) is a high-purity germanium spectrometer. The systemuses the Minimum–Mass Estimate method(see page 38) to confirm the isotopic com-position and the 239Pu mass threshold. The


Verification Methods: Attributes vs. Templates

The Trusted Radiation AttributesDemonstration System, orTRADS, uses a high-purity ger-manium detector to confirmattributes of the inspected item,a W84 warhead in this photo-graph. The detector is mountedinside the cart and the “trusted”processor and electronic com-ponents are on top of the cart.


presence of HEU is confirmed indirectlybased on the 2,614-keV emission from theisotope 232U, which is almost always pre-sent in HEU. Measurements are completedafter a 10-minute counting time. The frontof the sensor is located one meter from theaxis of the inspected item. There is no sizelimit for the inspected items. The analysisalgorithm is sufficiently robust to accom-modate the effects of intervening materials,so items ranging from small components tocomplete weapons can be inspected.

The TRADS uses a “trusted processor” toacquire and analyze data and to displayunclassified messages. The trusted processoremploys a divided architecture and softwaredesign that protects sensitive information.The needs of the inspecting party areaddressed by several features including easi-ly inspected components, a tamper-indicat-ing enclosure, and a secure hash algorithmfor software authentication.

Template ApproachThe fissile materials in nuclear weapons

emit gamma rays with spectral distributionscharacteristic of the isotopes contained inthe materials. Because gamma rays are scat-tered and absorbed by intervening materi-als, the gamma-ray distribution is alsoaffected by non-emitting materials. Theresulting spectra are sufficiently distinctiveto identify items by comparing a measuredspectrum with the template for the declaredtype. The template is created by measuringone or more items certified to be authentic.(The Russians use a similar approach butuse the term “passport” to describe what wegenerally call a template.)

The Radiation Inspection System (RIS) isan example of a template system. This sys-tem, originally developed to confirm theidentities of weapons and weapon compo-nents in a dismantlement scenario, measuresspectra with a sodium iodide detector. The

technology was derived from systems current-ly used for domestic safeguards to confirmthe identities of pits in containers.

Use of Templates in Arms Control andDomestic Safeguards

The greatest difference between arms con-trol and domestic safeguards applications isthe way in which the template database iscreated. Inspectors in international applica-tions cannot view spectra when the databaseis created, so authenticity must be certified inanother way. A certain degree of confidenceis obtained by allowing inspectors to ran-domly select items used in the benchmarkmeasurements that create the database.Confidence is augmented when the databaseis established by confirming attributes usinga system such as TRADS. This contrasts withdomestic applications where trusted individ-uals view the spectra, when measurementsare recorded to ensure that the characteristicsrepresent what are expected for the items.

Dean J. MitchellSandia National Laboratories



The Radiation Inspection System(RIS) uses a sodium iodidedetector to measure thegamma-ray spectrum of aninspected item. Identity is con-firmed if the measurementmatches the certified templatefor another item of the sametype. In a measurement at thePantex plant in Amarillo, Texas,RIS identified the item in only30 seconds. The system isportable and battery-powered.The detector operates at roomtemperature.

Information barriers are being studied inthe United States as well as in Russia (forexample, under the Warhead Safety and

Security Exchange agreement laboratory-to-laboratory program). These studies are mostoften conducted in conjunction with radia-tion measurement systems to help solvepotential monitoring problems with nuclearwarheads, warhead components, and thefissile material associated with warheads. Aradiation detection system information bar-rier consists of technology and proceduresthat prevent the release of sensitive nuclearinformation during a joint inspection of asensitive item, and it provides confidencethat the measurement system functionsexactly as designed and constructed. TheU.S. Government has been studying infor-mation barriers in a coordinated mannersince January 1997. Under the auspices ofthe Joint DOE–DOD Information BarrierWorking Group, a set of fundamentaldesign criteria have been developed andpeer reviewed by security specialists for thepurpose of guiding measurement system

developers for a wide variety of fissile mate-rial and warhead reduction agreementsbetween the United States and the RussianFederation.

Efforts had been underway to establish aU.S.–Russia Agreement for Cooperation,that would have enabled the exchange ofselected restricted data for the purpose ofmonitoring nuclear weapons and materialsagreements. Absent such an Agreement,information barriers probably offer theonly effective solution for the use of tech-nical measures, such as radiation measure-ment systems, on sensitive items andmaterials. Because the ionizing radiationemanations from a nuclear warhead consti-tute classified information in both the U.S.and Russia, relevant detection technologywill only be allowed—will only be useful—if information barriers have been engi-neered into the measurement system. It isstrongly believed by U.S. technical special-ists working in this area, and probablymost U.S. policymakers as well, that thesuccessful implementation of informationbarrier technology can only result from acooperative joint development effortinvolving all the parties associated withany particular negotiation.

Significant effort has been undertakenrecently to demonstrate to the RussianFederation and the International AtomicEnergy Agency the feasibility of integratinginformation barriers into radiation mea-surement systems. Attribute measurementsystems incorporating information barrierswere demonstrated for a U.S.–RussianFederation–International Atomic EnergyAgency audience in June 1999 and for aU.S.–Russian Federation audience in August2000. In addition, the concept was part of thePlutonium Production Reactor AgreementWorkshop in November 2000.

James FullerPacific Northwest National Laboratory


Information Barriers

A rack shields the electronic components as part of an information barrier incorporated into the FissileMaterial Transparency Technology Demonstration, held at Los Alamos National Laboratory in August 2000.




Certification and Authentication

Often mistaken for one another, certification and authentication are complementary processes.Certification of monitoring equipment by the host country establishes trust that no classified informa-tion is revealed during arms control or transparency measurements on sensitive items. An indepen-dent agency known as a certifying authority provides an unbiased assessment. Certifying authoritiesin the U.S. and Russia have stated independently that to be certified, a piece of equipment must besupplied by the host. For the monitoring party in turn to trust measurements using host-suppliedequipment, the opportunity to examine the equipment in detail and to witness its operation on non-sensitive substitutes for the controlled items must be granted. These operations, along with exhaus-tive evaluations of equipment design and construction, comprise authentication by the monitoringparty.

The certification process is well defined in both the U.S. and Russia and includes—• Security and vulnerability testing of hardware with information barriers• Testing and evaluating computers and software for processing classified data.

Requirements for authentication, however, are still being established as of this writing. Successfulauthentication will ensure the monitor that accurate and reliable information is provided by a mea-surement system and that irregularities, including hidden features, are detected. NNSA and DoDresearchers are crafting a model U.S. position for authentication that includes the following elements:• Functional tests using calibration sources• Evaluation of design documents and comparison to systems “as-built”• Evaluation of hardware and software• Random selection of equipment by monitoring party• Tamper-indicating devices, including tags, seals, and secure video recordings• Detailed human procedures accounting for all monitoring activities.

Certification and authentication share a concern for system reliability. Clearly, a system that mal-functions affects both the integrity of the measurement and the security of any classified informationwithin it. This argues for clarity of design and the sharing of design guidance between the host’s certi-fying authority and the monitor’s authenticating authority. The authorities are also interested in facil-ity decisions that can greatly affect the ease and cost of building the trust necessary for a system to beaccepted by both sides.

Richard T. KouzesPacific Northwest National Laboratory

James K. Wolford, Jr.Lawrence Livermore National Laboratory

START I is a treaty between the U.S.and the U.S.S.R. on the reduction andelimination of strategic weapons

signed in July 1991. Following the dissolu-tion of the U.S.S.R., Soviet START I obliga-tions were assumed by Russia, Ukraine,Belarus, and Kazakhstan—formerly Sovietrepublics with strategic nuclear weaponson their territories—under the LisbonAgreement of May 1992.

Among its many provisions, START I lim-its the U.S. and Russia (as the sole inheritorof Soviet nuclear warheads) to 1,600deployed ballistic missiles (bothIntercontinental Ballistic Missiles [ICBMs]and Submarine-launched Ballistic Missiles[SLBMs]) and heavy bombers for each coun-try. The treaty also limits each side to 6,000“accountable” deployed warheads of which

no more than 4,900may be on ballisticmissiles, 1,540 onheavy ICBMs (theSoviet SS-18), or1,100 on mobileICBMs. Complicatedcounting rules dis-count the numbersof bombs and mis-siles carried by heavybombers. A separate,politically bindingagreement limitseach side to 880

long-range (greater than 600 kilometers)Submarine-launched Cruise Missiles(SLCMs).

Other provisions of START I address war-head-downloading from ballistic missiles,new types of ICBMs and SLBMs, mobileICBMs, non-deployed missiles, exemptionsfrom treaty limits, verification, data denial,and treaty duration.

Weapon reductions are scheduled to becompleted by December 2001, seven yearsafter the treaty entered into force. START Ihas a duration of 15 years, unless changed

by mutual agreement, and may be extendedfor five-year intervals by agreement.

START II, built on the provisions ofSTART I, was signed in January 1993. It hasnot yet been ratified by Russia—a U.S. con-dition for beginning future negotiations.Both sides have subsequently agreed to shiftthe deadline for the completion of START IIreductions by five years to December 2007.

Under START II, the U.S. and Russia candeploy no more than 3,000 to 3,500 strategicnuclear warheads on ICBMs, SLBMs, andheavy bombers. No more than 1,700 to1,750 warheads can be deployed on SLBMs,and all Multiple Independently TargetedReentry Vehicle (MIRV) payloads must beeliminated on land-based missiles. MIRVpayloads on ICBMs and SLBMs may be“downloaded” to achieve a reduction indeployed warheads as well as ICBM “de-MIRVing.” The number of warheads onheavy bombers will no longer be discountedas they were in START I. In addition, up to100 bombers that have never been equippedfor long-range nuclear Altitude-launchedCruise missiles (ALCMs) can be shifted toconventional roles and will not be countedin the overall START limits.

Radiation Detection Equipment inMonitoring START

Annexes to the START I InspectionProtocol describe what and how radiationdetection equipment may be used for on-site inspections. In general, such equipmentconfirms that some inspected items are notnuclear. Specifically, a neutron source anddetection equipment used by U.S. inspec-tors may distinguish between long-rangenuclear and non-nuclear Russian ALCMsmounted on heavy bombers, and confirmthat containers do not hold long-rangenuclear-armed ALCMs.

Ronald L. OttLawrence Livermore National Laboratory


Strategic Arms Reduction Treaties(START): I and II

A Russian inspector examines acruise missile. (Photo courtesy ofDTRA)

Treaties, Agreements, and Initiatives



The INF Treaty

The treaty between the U.S. and the Soviet Union on the elimination of their intermediate-rangeand shorter-range missiles was signed on December 8, 1987. Known as the Intermediate NuclearForces (INF) treaty, it was the first treaty to allow one party to measure radiation from the nuclearwarheads of another party.

The treaty eliminated missiles and launchers but not warheads. During the negotiations, generalrules for conducting inspections were considered for a former missile site. Objects large enough tocontain a treaty-limited item would be subject to inspection. The inspection team would be permit-ted to bring documents and equipment, including radiation-detection devices. Because the Sovietsplanned to use SS-25 missiles at former SS-20 bases, and because the launch canisters of the SS-25are large enough to contain an SS-20 missile, the SS-25 missiles at former SS-20 bases would be sub-ject to inspection.

A special Verification Commission produced a Memorandum of Agreement (MOA) on the imple-mentation of the verification provisions of the treaty. The result was that a neutron detector wouldmeasure the neutron intensity pattern in the vicinity of the warhead section of the missile launch canister, and for certain cases, the end cap would be removed for visual observation of the warheadsection. Benchmark measurements were made on SS-20 and SS-25 missiles by a U.S. team in thesummer of 1989. This confirmed significant differences between the warheads of the two missile systems. The MOA, signed on December 21, 1989, contains a detailed description of the inspectionequipment and procedures for its use.

Keith W. Marlow and Dean J. MitchellSandia National Laboratories

The MRI Agreement

In March 1994, the then-heads of the Department of Energy, Hazel O’Leary, and Russian Ministryof Atomic Energy (Minatom), Viktor Mikhailov, signed an agreement to work jointly toward “mutualreciprocal inspections” (MRIs) of fissile materials removed from dismantled nuclear weapons. In pur-suit of this agreement, U.S. and Russian technical experts engaged in exchange visits during whichtechnological components of MRI were demonstrated, discussed, and ultimately, jointly researched.Demonstrations of and joint experiments with possible MRI technology occurred over the next twoyears at Rocky Flats, Lawrence Livermore National Laboratory (twice), and the Siberian ChemicalCombine located at the closed Russian city of Seversk (Tomsk-7).

No enduring inspection regime has yet resulted from the MRI agreement, but the technologyresearch and discussions have been seminal to nearly all of the other initiatives discussed here. Theattributes approach to confidence-building measurements draws heavily upon the MRI experience.Issues associated with protection of sensitive information through administrative and technical meanswere a regular theme in MRI exchanges. Finally, the MRI visits accomplished their objective of engag-ing U.S. and Russian technical experts to address the knotty problems now coming to light as themore structured transparency regimes develop. In this regard, the MRI exchanges can certainly beviewed retrospectively as successful.

M. William JohnsonLos Alamos National Laboratory

In accordance with the 1993 U.S.–RussiaHEU Purchase Agreement, 500 metrictons of highly enriched uranium (HEU)

from dismantled Soviet nuclear weaponswill be down-blended into low enricheduranium (LEU) hexafluoride over a 20-yearperiod. This LEU hexafluoride will be soldto the U.S. as fuel for commercial powerreactors. The Agreement also includes trans-parency monitoring by both parties toaffirm the nonproliferation objectives of theAgreement.

Russian deliveries began in 1995 with186 metric tons of LEU containing theequivalent of six metric tons of weapons-grade HEU while the transparency-monitor-ing arrangements were being worked out.Under the Agreement, the U.S. has theright to send technical experts to the fourRussian plants that process HEU to LEU(see map). Up to six 5-day monitoring visitsare allowed each year at each Russian plant.

Also according to the Agreement, a per-manent monitoring office was establishedin 1996 at the Ural ElectrochemicalIntegrated Enterprise (UEIE) in Novouralsk.Transparency monitoring began in 1996with visits to UEIE and the SiberianChemical Enterprises (SChE) in Seversk.Monitoring at the Electro-Chemical Plant(ECP) and the Mayak ProductionAssociation began in 1997 and 1998,respectively.

U.S. monitors access storage and processareas. They inspect containers of HEUweapons components, HEU metal chips,HEU oxide, HEU hexafluoride, and LEUhexafluoride. They witness the burning ofHEU metal chips to HEU oxide and observethe input and output of processes of purifi-cation of HEU oxide and conversion of HEUoxide to LEU hexafluoride. They alsoinspect equipment where HEU (90%enriched) is down-blended (as gaseous ura-nium hexafluoride) with 1.5%-enriched LEUto produce LEU in power-reactor enrich-ments from 3.6% to 4.95%.

Visual observation by technical experts iskey to transparency monitoring. Theexperts’ effectiveness is enhanced signifi-cantly by using U.S. monitoring equipmentin the Russian plants (see pages 51 and 52).Since 1997, portable nondestructive assayequipment has confirmed the enrichmentof HEU (in its various forms used in Russianprocessing) by measuring the intensity ofgamma rays from 235U.

The U.S.-developed Blend-DownMonitoring System (BDMS), which confirmsthe flow and enrichment of uranium hexa-fluoride in the down-blending process,continuously monitored the blending ofeight metric tons of HEU at UEIE during1999. An enrichment monitor compares


Transparency Measures for theU.S.–Russia HEU Purchase Agreement


The Blend-Down Monitoring System (BDMS) consists of a flow monitor and an enrichment monitor foreach pipeline in the Russian down-blending facilities.



235U gamma rayswith the attenuation ofgamma rays from a 57Cosource. A flow monitor uses a modulated252Cf neutron source to induce fission of235U atoms flowing in the pipe and a down-stream gamma-ray detector to measure thetime delay for the fission products arrivingat the detector (see page 50). The BDMS, forthe first time, directly measures the quantityof HEU blended at the UEIE. Similar equip-ment will be installed at ECP and SChE.

Through February 2000, 81.3 metric tonsof Russian HEU has been down-blended toLEU and shipped to the U.S. An additional30 metric tons are scheduled for delivery in2000, and at least 30 metric tons in eachsubsequent year until the agreed amount isreached. Actual quantities each year aredetermined by a contract between theUnited States Enrichment Corporationand Techsnabexport, the commercialarm of Minatom.

Douglas A. LeichLawrence Livermore National Laboratory

Ed MastalDepartment of Energy, Germantown, Maryland

Westinghouse Fuel Fabrication Facility Columbia, South Carolina

GE Nuclear Energy Wilmington, North Carolina

WASHINGTON, D.C.

Framatome Cogema FuelsLynchburg, VirginiaABB/Combustion Engineering

Hematite, Missouri

LEU

Portsmouth, Ohio

UNITED STATES

LEU OxideLEU

Novouralsk (UEIE)

LEU

LEU

LEU

St. Petersburg

HEU LEU

Ozersk(Mayak)

HEU Oxidation

MOSCOW

To U.S.

HEU

HEU HEU LEUSeversk(SChE)

HEU Oxidationand HEU LEU

Zelenogorsk (ECP)

RUSSIA

HEU

HEU LEU

Power CorporationSiemens Power CorporationWRichland, Washingtonashington

Siemens Power CorporationRichland, Washington

Converting Weapons-Grade HEU(90% enriched) to LEU

• The HEU-metal component is removedfrom a nuclear weapon.

• The component is machined into metalshavings.

• The metal shavings are heated andconverted to an oxide.

• Any contaminants are chemically removedfrom the HEU-oxide.

• The HEU-oxide is converted chemicallyinto uranium-hexafluoride gas.

• The uranium-hexafluoride gas is dilutedwith a much lower enrichment level of ura-nium-hexafluoride gas, producing an LEU-hexafluoride gas for nuclear-fuel fabrication.

• Cylinders are filled with the LEU-hexafluoride gas.

• The cylinders are shipped to the U.S.,where they are delivered to nuclear-fuelmanufacturers to make fuel rods for commercial nuclear-power plants.

Located in formerly secret cities of the Sovietnuclear-weapons complex, four plants processweapons-grade HEU to LEU for nuclear-reactor fuel:the Siberian Chemical Enterprises (SChE) atSeversk, the Ural Electrochemical IntegratedEnterprise (UEIE) at Novouralsk (also referred to asthe Urals Electrochemical Integrated Plant, UEIP),the Mayak Production Association (MPA) at Ozersk,and the Electro-Chemical Plant (ECP) atZelenogorsk.



In 1992, Russia requested U.S. assistancefor the construction of a fissile materialstorage facility, explaining that a lack of

adequate storage capacity was delaying theRussian nuclear-warhead dismantlementprocess. In response to this request, theDepartment of Defense, under itsCooperative Threat Reduction (CTR) pro-gram, committed to assist Russia in con-structing a facility at Mayak to store fissilematerial from dismantled nuclear warheads.When completed in 2002, the initial12,500-container-capacity facility will becapable of storing plutonium from morethan 6,250 nuclear weapons.

Ongoing negotiations on a transparencyregime for Mayak are intended to provideconfidence that: (1) the material stored atMayak is from dismantled nuclear weapons;(2) the stored material is safe and secure;and (3) any material withdrawn from Mayak

is not used for nuclear weapons. The U.S.and Russia have agreed on these objectivesas well as the specific procedures necessaryto meet the second and third objectives.Negotiations continue on procedures tomeet the first objective. The challenge toreaching complete agreement is ensuringadequate protection of sensitive nuclear-weapons information.

Russia is concerned that any measure-ments confirming the derivation of storedfissile material from nuclear weapons couldreveal sensitive information about itsnuclear weapons. To address this concern,the U.S. has proposed a suite of attributesthat employ threshold measurements andinformation barriers designed to protectsensitive information (see page 6).

Jessica Amber KehlOffice of the Secretary of Defense

Mayak Transparency

Artist’s concept of completed facility. Mayak Fissile Material Storage Facility under construction at Ozersk,Russia. (photo courtesy of DTRA).

PrimaryStorage

Area



Fissile Material Cut-off Treaty

The UN General Assembly, the Conference on Disarmament,and the 1995 and 2000 Non-Proliferation Treaty ReviewConference have all endorsed the negotiation of a ban on theproduction of fissile material for nuclear weapons and othernuclear-explosive devices, but these negotiations are unlikely tobegin in the near future.

FMCT States Parties would be prohibited from producinghighly enriched uranium and plutonium for nuclear weapons.They would also be obligated to accept measures to verify thatall fissile material produced after the cut-off date is not used fornuclear weapons or other nuclear-explosive devices and todetect undeclared production. These obligations would be non-discriminatory.

The U.S. has identified verification arrangements that itbelieves would be effective and efficient. Under these arrange-ments, “fissile material” would be defined as plutonium-239 anduranium enriched to 20% or greater in the isotopes 235U and233U, separately or in combination, and any material containingone or more of the foregoing. “Produced” would be defined asthe separation of irradiated nuclear material and fission products,or increasing by a process of isotopic separation the abundanceof 235U or 233U in uranium or 239Pu in plutonium. (Incidentalisotopic or fission-product separation resulting from chemicalprocesses would not be considered production.)

The verification regime would consist of routine monitoring ofdeclared production facilities to verify State Party’s declarations,envisioned to be carried out by the International Atomic EnergyAgency; consultation and fact-finding to resolve questions aboutcorrectness and completeness of, or inconsistencies related to,information provided by a State Party; and nonroutine inspectionsto resolve questions regarding possible undeclared production.

In the Mayak Storage Facility, a crane lowers the fissile material into a“nest,” a cylindrical space several meters in length in which theAT-400Rs are stacked.

Adelegation of Russian officials visitedLos Alamos National Laboratory fromAugust 14–17, 2000 to observe a suc-

cessful demonstration of a new technologyfor monitoring nuclear materials removedfrom military programs. By combininginnovative data barriers and a simple yes/nodisplay, U.S. scientists assured the Russiandelegation that the nuclear-material samplebeing tested had the declared bomb-gradecharacteristics.

The Russian delegation, headed by a rep-resentative of the Ministry of AtomicEnergy, observed the Attribute Measurement

System with Information Barrier technology(AMS/IB). When fully developed, this sys-tem will protect sensitive information whileproviding increased confidence that U.S.and Russian fissile materials have beenproperly certified, packaged, and stored.

The technology being developed measuresthe radiation emitted by the fissile materials.These radiation signatures give observersconfidence that the packages contain fissilematerial. The attributes evaluated includedthe presence of plutonium, plutonium iso-topic ratio, mass, absence of plutoniumoxide, symmetry, and age of the plutonium.

During the demonstration, these attributeswere measured with commercially available,high-resolution gamma and neutron detec-tors assembled by a multi-laboratory team.Data from the detectors were sent to a com-putational block where they were analyzedand compared to threshold values. A pass/failsignal was sent through information protec-tion technology to a display with a series ofred and green lights. No sensitive data wereemitted from the measurement system.

The Departments of Energy and Defenseand the Defense Threat Reduction Agencyare jointly developing the technology toensure the safe and secure storage of excessfissile material from the Russian nuclear-weapons program. U.S. and Russian officialsdiscussed the joint development of a similarsystem in Russia. The technology demon-strated to the Russian delegation at LosAlamos was part of the Cooperative ThreatReduction program in conjunction with theMayak Fissile-Material Storage Facility inOzersk, Russia.

The U.S. and the Russian Federationshare a common interest in maintainingand improving the safety and security of fis-sile material. Related work being carried outunder the Cooperative Threat Reductionprogram with Russia includes the provisionof over 12,000 transportation and storagecontainers for Russian fissile material andconstruction of the storage facility in


Fissile Material Transparency Technology Demonstration


Open Mode

Sample Isotopics? Mass? No Oxide? Pu Present? Symmetry? Age?

ZPPR plates in “dumb bell” ● ● ● ● ● ●configuration

Large oxide sample ● ● ● ● ● ●upright

Secure Mode

Weaponcomponent ● ● ● ● ● ●

Large oxidesample on ● ● ● ● ● ●its side

The output lights from the various tests are simple to read. The easiest way to interpret the results is toask the following questions. Does this fissile material sample meet the isotopic ratio criteria for weapons-grade plutonium? Does this sample mass exceed an agreed-upon threshold? Is plutonium oxide absent?Is plutonium present? Is the plutonium in a symmetrical shape? Is the plutonium older than an agreed-upon date? A green light indicates a positive answer to the question while a red light indicates a negativeanswer. The samples tested were Zero Power Physics Reactor (ZPPR) plates; fuel-grade plutonium metal;1.75 kilograms of plutonium oxide; and a nuclear-weapon pit. The equipment performed flawlessly, giv-ing all the proper responses in each test.


Ozersk. When complete, the storage facilitywill be capable of the safe, secure, and envi-ronmentally sound long-term storage of atleast 30 metric tons of fissile materialexcessed from Russia’s weapons program.An AMS/IB system jointly developed as a

follow-on to this initiative could beinstalled in the storage facility as an integralpart of a joint monitoring system.

Larry AvensLos Alamos National Laboratory


Both photos show the AttributeMeasurement System with anInformation Barrier used in theFissile Material TransparencyTechnology Demonstration,August 2000. The nuclear-mate-rial package is contained in theblue Neutron MultiplicityCounter (right photo, center).The shielded electronics rackcontains the computationalequipment that analyzes thedata (left photo). The readoutdisplay is mounted on top ofthe electronics rack (see illustra-tion, previous page.

Attribute Measurement System with Information Barrier Technology

Many of the attributes discussed in the “Treaties, Agreements, and Initiatives” section can be measured using traditional, non-destructive assay methods. Although these measurement techniques are well established, they become problematical if the itembeing measured is classified. Because useful radiation data generated from a classified item is generally classified, the data mustbe protected and not displayed directly during a measurement. An information barrier (IB) that protects the classified informationmust perform two functions:

1. The IB prevents the release (either accidental or intentional) of classified information.2. The IB, at the same time, provides confidence that the measurement systems are functioning correctly and that the unclassi-

fied display reflects the true state of the measured item. (This is often referred to as the “authentication problem.”)

An Attribute Measurement Systems incorporating an IB was shown to a Russian Federation audience in August 2000 at theFissile Material Transparency Technology Demonstration. In this demonstration, hardware and software combined with proce-dures addressed both requirements of the IB.

The IB was designed with the needs of authentication in mind. Each element of the measurement system (including the IB)should be simple and easy to inspect and should not have any extraneous functions. If the measurement system is composed ofsimple building blocks, or modules, then the function of each element can be well defined. Similarly, if each of the protective fea-tures is simple, then it is straightforward to verify that the protective functions of the IB are operating as specified.

Duncan MacArthurLos Alamos National Laboratory

In September 1996, the Secretary ofEnergy, the Russian Federation’sMinister of Atomic Energy, and the

Director General of the InternationalAtomic Energy Agency (IAEA) came togeth-er under the Trilateral Initiative to explorethe technical, legal, and financial issuessurrounding IAEA inspections of nuclearmaterials removed from defense programs.The technical work has focused primarilyon developing approaches that would per-mit the IAEA to conduct its inspectionswithout violating Article I of the Non-Proliferation Treaty (NPT), which forbidsthe sharing of nuclear weapons informa-tion with nonnuclear weapons states.Opposing this absolute requirement(which is also codified in the U.S. AtomicEnergy Act) is the need for the IAEA toconduct credible, independent inspectionsto assure the world that excess nuclearmaterials removed from defense programsare not returned to nuclear weapons.Because much of the excess materials arecurrently classified and will not be con-verted to unclassified forms for many

years, technologies and procedures to per-mit inspections of these materials canmake an important contribution to excessmaterials verification.

The challenges presented by the TrilateralInitiative are in fact common to manypotential arms control and arms reductiontreaties and agreements, including futurearrangements that might involve warheaddismantlement transparency, verification ofplutonium disposition in the U.S. andRussia, and U.S. inspections of Russianmaterials to be stored in the Mayak FissileMaterials Storage Facility (see page 12).

The Department of Energy’s InternationalSafeguards Division was tasked with sup-porting a Trilateral Initiative working group.A team with members from LawrenceLivermore, Los Alamos, Pacific Northwest,and Sandia National Laboratories held anumber of workshops and technical meet-ings with Russian and IAEA scientists todevelop an approach to inspecting excessnuclear materials with their inherent classi-fied characteristics. Key to the concepts thatemerged from these meetings was the ideaof an information barrier concept (see page6). The challenge was to take this informa-tion barrier and turn it into a workableinstrument that satisfies very stringent securi-ty requirements.

The Prototype Inspection System withan Information Barrier was the first realiza-tion in hardware and software of a mea-surement system with an information bar-rier for fissile-material transparency mea-surements. The working group focused ona system capable of determining plutoni-um mass and the presence of weapons-quality plutonium in sealed storage con-tainers. Plutonium mass is measured usingneutron-multiplicity coincidence counters(see page 37). Gamma-ray spectrometrydetermines the ratio of 240Pu to 239Pu.Both sets of these classified measurements


The Trilateral Initiative: AttributesVerification


The Trilateral Initiative working group has participated in several workshops and technical demonstrationsin an effort to identify challenges and difficulties in the IAEA inspections.



are then compared with unclassifiedthreshold values, determining if containersof classified materials should be acceptedinto IAEA verification. This “attributes”verification approach results in simple one-bit information (yes/no) for the inspectorsthrough an information barrier.

The conventional wisdom of most partici-pants early on was that an information bar-rier would be implemented in software;however, authentication of software toensure both security and IAEA independencewas recognized as a formidable challenge.The DOE/NNSA drew on the expertise oftheir U.S. colleagues, the IAEA, and theRussian nuclear institutes (All-RussianScientific Research Institute of ExperimentalPhysics, All-Russian Scientific ResearchInstitute of Technical Physics, and theInstitute for Physics and Power Engineering).

The team developed a modular conceptthat clearly separates data acquisition from“computational block” (where measure-ments are compared to the attribute thresh-olds). This modular concept includes a databarrier implemented in hardware. Thisensures that only yes/no information istransmitted outside the shielded enclosurecontaining all of the electronics and com-puters (and their classified information).Other concepts included “volatile” memory,a “security watchdog” that removes powerand thus erases data if the enclosure isopened or if tampering is detected, and thepotential to operate the system in “secure”and “authentication” modes. In the authen-tication mode, the IAEA can calibrate withunclassified nuclear materials to ensure thatthe instrument will perform properly in thesecure mode, permitting independentauthentication of the instrument by theIAEA. The totality of these ideas is unique,providing the required information barrierthat is both flexible and relatively straight-forward to implement.

The team, working with a larger support-ing cast from DOE/NNSA, successfullydemonstrated its information barrier con-cepts, and as a result, has begun the nextphase of the Trilateral Initiative’s technicalefforts: the development of technicalrequirements and specifications for theactual inspection systems. It is noteworthythat in the Trilateral Initiative’s consulta-tions, the Russian representatives haverepeatedly pointed to the success of thetechnical working group and have supportedongoing development of the next phase ofinformation barrier technology.

James TapeLos Alamos National Laboratory

The prototype Inspection System with an Information Barrier was demonstrated at Los Alamos NationalLaobratory to technical delegations from the Russian Federation and the IAEA in late June 1999. On theleft is a neutron multiplicity counter to determine plutonium mass. On the right, in an anodized shieldedenclosure, is a high-resolution gamma-ray detector to determine the presence of “weapons-quality” plutonium. In the center background is an equipment rack containing the data-aquisition equipment andthe computers that controlled data aquisition and analyzed the data. In the center foreground is the smallbox with red and green lights that provided the pass/fail indications for the items measured during thedemonstration.

Then-Vice-President Gore and then-Prime Minister Chernomyrdin signedthe Agreement Between the Government

of the United States of America and theGovernment of the Russian FederationConcerning Cooperation Regarding PlutoniumProduction Reactors on September 23, 1997.The Plutonium Production ReactorAgreement (PPRA) requires the implementa-tion of measures to ensure that plutoniumproduction nuclear reactors currently shutdown in both countries do not resume oper-ation. Additionally, the last three Russianproduction reactors will be converted to anoperating mode that does not produceweapons-grade plutonium. Plutonium oxideproduced in the interim from the operatingreactors’ spent fuel will be monitored toensure that it is not used in weapons.According to the Agreement, measurements

take place twice a year after the first Russiandeclaration.

Twenty-four shut-down production reac-tors are covered under the PPRA at threesites in Russia (Ozersk, Seversk, andZheleznogorsk) and at two sites in the U.S.(Hanford, Washington and Savannah River,South Carolina). Currently in the secondyear of monitoring, the monitoring mea-sures at the shut-down reactors include theinstallation of seals or visual monitoring atthe reactors not deemed to have been irre-versibly dismantled. Annual monitoring vis-its are made to the shut-down reactors toensure that they remain shut down.

The PPRA estimates that between 4.5 and9 metric tons of plutonium oxide will bemonitored. Monitoring provisions for theplutonium oxide include checking tags andseals on containers in storage, as well asmeasurements on a random sample of thecontainers, to determine if the mass of thecontainer is as declared and whether thematerial is “weapons-grade” (i.e., comesfrom low-burnup fuel) and has been newlyreprocessed. To date, no monitoring of plu-tonium in storage has occurred.

The material is considered weapons-gradeif the plutonium isotopic ratio of 240Pu/239Puis less than 0.1. Determining the elapsed time(age) since the plutonium was chemicallypurified tells us whether the material is newlyprocessed (see page 31). Both attributes willbe measured with a high-purity germaniumgamma-ray detector and analyzed with astandard isotopics code. It has been proposedto measure the mass of the plutonium with aneutron multiplicity counter (see page 37).

The isotopics of plutonium is classifiedinformation to the Russians; therefore, thishas resulted in the concept of informationbarriers to collect—but not reveal—classifiedinstrument data, process those data, andpass an unclassified yet meaningful result to


U.S.–Russia Plutonium Production Reactor Agreement


The U.S. is exploring the use ofthe Russian Greenstar data-acquisition card as part of theradiation-monitoring equipmentfor the PPRA.



A Core-Discharge Monitor

The core-discharge monitor, pictured,determines when nuclear material movesfrom one place to another. This material ischaracterized as irradiated fuel pellets or someother material, providing data for nuclearsafeguards or control and accountability. Thecore-discharge monitor is based on a subsetof hardware used by DOE and theInternational Atomic Energy Agency for secu-rity and safeguards applications, respectively.The redundant system runs in anautonomous, unattended mode for theinspection period.

This application quantifies the amount ofgross neutron or gross gamma radiation, but itdoes not give quantitative information on thenuclear material present. Ratios of gross radia-tion determine the type of material flowingpast the detector, e.g., irradiated fuel or poi-son slugs. Sampling time is in fractions of sec-onds. A cadmium–telluride detector provides amedium-resolution gamma spectrum of thematerial as it flows by. It does not measure theisotope content, but rather determines itspresence. This is helpful in determining differ-ences among the various types of materials.

In this application, the speed at which thefuel moves is a challenge to the design. Fieldexperience on second-generation equipmentexceeds four centuries of continuous systemoperation with fewer than five documentedcases of loss of safeguards’ continuity.

James HalbigLos Alamos National Laboratory

IntegratedCircuit 3He

FuelCdTeDetector

1024-ch Multichannel

AnalyzerReactorChannel

Mini-GRANDMini-GRAND

an inspector (see page 6). Measurementsresult in yes/no answers for declared mass,isotopics, and age since chemical separation.

Monitoring—after the reactors cease pro-duction of weapons-grade plutonium—would confirm the composition of fuelloaded and verify that fuel is not dischargedearly. This is accomplished through themeasurement of random samples of freshfuel and the installation of a monitoringdevice in the fuel discharge area to detectreactor fuel discharges. The reactors will beshut down after fossil-fuel plant replace-ments are operational or no later than atthe end of their normal lifetimes, consistentwith prudent safety considerations andamendment of the PPRA.

A Joint Implementation and ComplianceCommission (JICC) oversees implementa-tion of the PPRA’s provisions, resolves anyissues that may arise, and considers addi-tional measures to promote the objectivesof the Agreement. The JICC has met fourtimes: December 1997, October 1998,February 2000, and September 2000.

Technical discussions to work out someoperational details were held at Los AlamosNational Laboratory in November 2000. APPRA-specific demonstration is being pro-posed at Lawrence Livermore NationalLaboratory. Integrated detectors that are eas-ier to replace and easier to authenticate willbe demonstrated. The isotopic ratio of240Pu/239Pu, age since chemical purifica-tion, and mass of plutonium will be mea-sured.

Michele SmithU.S. Department of Energy

Zachary KoenigLawrence Livermore National Laboratory



The United States government is cur-rently considering a broad range ofpossible nuclear arms reduction mea-

sures consistent with our evolving nationaland international security context.Scientists and engineers have been develop-ing a flexible and robust set of monitoringtechnologies to support the measures basedon guidelines derived from previous accordsand statements.

Previous agreements and accordsaccounted for deployed warheads as attrib-uted to their delivery systems. Thus, deliv-ery-system reductions were the primaryfocus of U.S.–Russia verification activities.While future reductions may continue tofocus on warhead-delivery systems, there isan interest in accounting for the destructionof both the warhead and the nuclear mate-rials associated with that warhead. If thenuclear materials are not mechanically orchemically altered, they would be placed inlong-term, monitored storage facilitiesdesigned to ensure that the materials arenot re-used for defense-related purposes.

In an effort to promote the irreversibilityof reductions and ensure the internationalcommunity that the U.S. is meeting itsNuclear Non-Proliferation Treaty (NPT)commitments, several U.S. and jointU.S.–Russia programs are currently focused

on issues related to the transparency ofstrategic-nuclear-warhead inventories, thestorage and handling of nuclear materials,and the destruction of strategic nuclear war-heads. The details and technologies to beemployed for many of these arms reductionand transparency measures have yet to beworked out or are under active negotiation.It is anticipated that these measures willrequire the development of innovative tech-nological solutions. A new type of require-ment associated with many of these mea-sures and agreements is the simultaneousneed for information barriers to protect thehost country’s sensitive information andauthentication technologies to provide themonitoring party with the confidence thatmeasured data can be trusted. The majorareas of consideration for these applicationsinclude warhead and special nuclear materi-al identification based on radiation detec-tion, warhead and material monitoring,tamper-indicating devices such as tags andseals, and technological alternatives to radi-ation detection. Different technologies needto be developed to support measurementinstrumentation ranging from field size,point-of-use equipment to large stationaryinstallations.

Carolyn PuraSandia National Laboratories

Future Arms Reduction Initiatives

U.S. and Russian scientists discussthe Fissile Material TransparencyTechnology Demonstration atLos Alamos National Laboratoryin August 2000.



-12The Comprehensive Test Ban Treaty (CTBT)

bans any nuclear explosion anywhere in theworld. The product of four decades of multilateraleffort, it was opened for signature in September1996. To enter into force, the CTBT has to be rati-fied by the 44 nuclear-capable states that formallyparticipated in the 1996 Conference onDisarmament who possess nuclear power andresearch reactors as listed in the treaty. As ofFebruary 2000, the CTBT has been signed by 155 nations and ratified by 53. Although the U.S.Senate voted in 1999 not to ratify the treaty, itremains on the Senate calendar and could bevoted on again at any time. Former Secretary ofState Madeleine Albright recently announced theappointment of General John Shalikashvili to“construct a path that will bridge any differencesand ultimately obtain Senate advice and consentto the treaty.”

The challenges in CTBT monitoring are todetect very-low-yield nuclear explosions (aswell as any conducted under conditions

intended to mask the signals) and to distin-guish them from other sources. The treaty callsfor networks of atmospheric, underground,and oceanic sensors integrated into anInternational Monitoring System. Data flowscontinuously between National Data Centers(NDCs) and an International Data Center(IDC). The center at Patrick Air Force Base ana-lyzes the U.S. data. The IDC processes the datato produce event bulletins and to screen outevents that are very unlikely to be nuclearexplosions. The NDCs are responsible fordetermining if an event violates the treaty.

Monitoring is complicated by similaritiesbetween the effects from nuclear explosions andthe effects produced by non-nuclear sources.Also, signals are distorted or blurred as they passthrough geologic structures. To meet the chal-lenge, work is needed on data analysis techniquesthat will ensure timely assessments of events anddata collection that will calibrate the sensor net-works to account for geologic structures.

The Comprehensive Test Ban Treaty

Jay ZuccaLawrence Livermore National Laboratory

Facilities


The Pantex Plant is America’s onlynuclear-weapons assembly and disassemblyfacility. Located 17 miles northeast ofAmarillo, Texas, Pantex is centered on a16,000-acre site. The plant’s primary missionis stockpile stewardship of U.S. nuclearweapons. Operations include assembly, disas-sembly, refurbishment, maintenance, modifi-cation, and evaluation of nuclear weapons,plus interim storage of plutonium pits.

Pantex was originally a conventionalbomb plant for the U.S. Army during WorldWar II. Ten months after Pearl Harbor, thefirst bomb came off the assembly line. Aswith many World War II-era munitionsplants, Pantex was deactivated after the warended. In 1951, at the request of the AtomicEnergy Commission (now NNSA), the Armyreclaimed the plant for use as a nuclear-weapons production facility. By 1975,Pantex was the only facility for the assemblyand disassembly of nuclear weapons. InSeptember 1991, the last new nuclearweapon was assembled.

To maintain the reliability of the nation’sweapons stockpile, a number of randomlyselected warheads from all active systemsare removed from the stockpile andreturned to Pantex each year for surveillance,testing, and evaluation to determine if thecomponents are in good working order.

The weapons are disassembled andinspected. Then certain components areassembled into test configurations and sub-

jected to electrical and/or explosive testing.Evaluation of warheads using this disassem-bly and inspection process is a part ofNNSA’s Stockpile Stewardship strategydesigned to ensure high confidence in thesafety and reliability of the weapons stock-pile without nuclear testing.

With the U.S and Russia reducing theirnuclear-weapons stockpiles in accordancewith Presidential declarations, Pantex plays avital role in this effort. Most of the weaponssent to Pantex for disassembly were original-ly assembled at Pantex. The dismantlementof nuclear weapons is not a new process asNNSA has disassembled approximately60,000 nuclear weapons over the yearsthrough all its predecessor agencies.

Interim Plutonium StorageThe bulk of nuclear-material parts disas-

sembled from nuclear weapons is traditional-ly returned to the NNSA plants that original-ly manufactured the parts. However, due tothe end of plutonium processing at theRocky Flats facility in Colorado, Pantexserves as the storage site for the plutonium"pits." A pit—the core of a nuclear weapon—contains plutonium hermetically scaled in ametallic shell.

As an assembly-and-disassembly facility,Pantex has long had the capacity to stage pitsas they were coming and going. As the stor-age site, Pantex will store all U.S. pits inexcess of 20 years or until final disposition forthe pits is determined.

Arms ControlIt is conceivable that a future arms con-

trol treaty will directly affect Pantex. Inpreparation for this possibility, Pantex hashosted a series of NNSA-sponsored initia-tives to evaluate technologies that havebeen designed by NNSA’s national labora-tories that could be used in future armscontrol treaties.

Leigh BratcherPantex Plant

The Pantex Plant


Facilities

The Savannah River Site (SRS) is ready-ing a storage facility for storingweapons-grade plutonium from dis-

mantled nuclear weapons. The K AreaMaterial Storage (KAMS) project provides aplace to store excess plutonium in the yearsbefore new disposition facilities come online at SRS. The Rocky Flats EnvironmentalTechnology Site, for instance, can save mil-lions of taxpayer dollars if it ships its pluto-nium out in the near future, rather thanwaiting for the new facilities. That materialcan be held in KAMS until the new disposi-tion facilities are ready.

In January 2000, Secretary of Energy BillRichardson issued a Record of Decision onthe Surplus Plutonium DispositionEnvironmental Impact Statement designat-ing the SRS as the recipient of three newplutonium disposition facilities. This makesSRS the nation’s cornerstone for excess plu-tonium disposition. Shipments will start in2001. The total capacity when completedwill be 3,000 shipping containers.

KAMS is the first step in preparing for thenew disposition facilities. It is located in105-K, the building that formerly housedthe K Reactor, which produced nuclearmaterials during the Cold War for nearlyfour decades. It was the United States’ lastoperating production reactor, shuttingdown for the last time in 1992.

The KAMS project was chosen as thenational solution for several reasons:• The facility underwent stringent, well-

documented earthquake and structuralupgrades during a restart campaign in theearly 1990s.

• It is a robust building, constructed ofconcrete walls many feet thick.

• Much of the security infrastructure isalready in place. Security in 105-K hasbeen enhanced, and access to the build-ing is limited to essential personnel only.

• Necessary modifications were relativelyminor, compared to the cost benefit.Security is ensured through a system

called a radio-frequency tamper-indicatingdevice (RFTID), developed by SandiaNational Laboratories. This system usesthin, fiber-optic wires, used with storagedrum arrays, which indicate possible tam-pering with drum storage.

Also, material balance and accounting ishandled via neutron multiplicity countersdeveloped by Los Alamos NationalLaboratory for neutron detection. Operatorsconfirm the container record by a neutronmultiplicity counter, built by Canberra.

The transition from reactor production toplutonium storage closes a circle that beganin the early 1950s, when K and four otherreactors at Savannah River began producingplutonium and tritium for the nationaldefense. Now, the nation’s plutonium fromweapons dismantlement will be disposed ofthrough three new operations planned forSRS—the mixed-oxide fuel fabrication facility,the plutonium immobilization facility, andthe pit disassembly and conversion facility.

Frances PodaWestinghouse Savannah River CompanySavannah River Technology Center

Savannah River Site’s K Area Material Storage Project


“Trust but verify.” By using asimulated Soviet SS-20, instru-mentation is developed fortreaty verification at the TA-18facility at Los Alamos NationalLaboratory.

Facilities

The unique capabilities for handlingnuclear materials at Technical Area 18(TA-18), coupled with Los Alamos

National Laboratory’s expertise in experi-mental measurements and sensor develop-ment, are vital to threat reduction programsat every level. Future treaty-verificationefforts and nonproliferation missions can-not credibly be conducted without suchfacilities and expertise. Fundamentally, thearms control initiatives will result in a sig-nificant buildup of excess nuclear weaponsmaterials, leading to more densely config-ured storage of these materials, i.e., to con-figurations of greater concern with regard tocriticality.

Thus, as a first requirement, both armscontrol treaties in particular and nonprolif-eration in general require the capability tofabricate and characterize realistic nuclearassemblies constructed from Category I

quantities of nuclear materials. Furtherrequired are the development and evalua-tion of new nuclear measurement anddetection technology. TA-18 can respond tothese requirements by providing a test bedto advance the technology for automatedfacility monitoring. Beyond materials andequipment, the training programs for lawenforcement and other government person-nel are an essential part of the TA-18 mis-sion, as are criticality safety training andfirst-responder training.

Equipment for arms control, nuclearmaterials disposition, and waste manage-ment receive realistic tests and objectivevalidation through the Los Alamos CriticalExperiments Facility (LACEF) and otherTA-18 capabilities. Some concepts andequipment are developed at other DOElocations and brought to TA-18 for evalua-tion; others are developed at TA-18 withspecial nuclear materials. Among the contri-

TA-18 at Los Alamos National Laboratory


Facilities

butions in this arena are the invention,development, and technology transfer ofportal monitors, waste management, andhand-held radiation detection and analysisequipment, as well as the development andevaluation of transparency regimes.

LACEF operations are centered aroundthree specially designed laboratory build-ings that house critical assemblies withremote capabilities. Each building has its

own storage vault. An additional laboratoryis available for short-term use of specialnuclear materials for hands-on measure-ments. The facility also provides linearaccelerators, x-ray generators, and neutrongenerators, as well as the necessary expertiseto assist experimenters.

Richard MalenfantLos Alamos National Laboratory

Observations with sophisticatedinstruments on a surrogatenuclear weapon are necessaryto develop mutual trust whilepreserving security.


The RMF’s main bay is 50 x 50 x 30 feet high. In the center of thebay, rising 12 feet above the floor, is a 20 x 20-foot platform. Thislow-scatter platform, with its aluminum-grating floor, keeps the radia-tion source and the various radiation detectors as far as possible fromthe concrete walls, floor, and ceiling of the bay. The structure of theplatform minimizes the amount of reflected radiation seen by thedetectors. The floor of the bay is available for measurements whenradiation scattering and background are of less concern.

Facilities

For over a quarter-century, as a result ofconcern for the health and safety ofthose who handle nuclear weapons

and components, Lawrence LivermoreNational Laboratory has been active in mea-suring the intrinsic nuclear radiation emit-ted by such assemblies. During this period,Livermore has had a succession of speciallydesigned facilities wholly dedicated to high-quality radiation measurements of compo-nents and assemblies containing fissilematerials. Each of these has improved andexpanded these capabilities. The latest ofthese specially designed measurement facili-ties was opened for business in 1988. TheRadiation Measurement Facility (RMF) isunique in the United States and is comple-mented by Livermore’s long experience innuclear-radiation measurements.

Within the RMF, we can make high-quali-ty neutron and gamma radiation measure-ments of sources containing fissile materialwith little corruption from room return orbackground. Located in Livermore’sSuperblock, the RMF is specially designed topermit "free-field" measurements of spectraland dose fields around nuclear explosive-

like assemblies (NELAs) containing plutoni-um and uranium parts and inert highexplosives, although its use is not limited tothose materials.

The standard instrument suite within theRMF includes high-purity germanium andsodium iodide gamma-ray detectors; a high-accuracy dePangher Long Counter for neu-tron flux; Bonner spheres for neutron spec-tra; and a variety of neutron- and gamma-dose measuring detectors. A wide variety ofcommercial and NIST-standardized neutronand gamma-ray calibration sources arelocated in a shielded well in the bay floor.Visiting experimenters do, of course, bringtheir own equipment as well.

Programmatic areas of RMF use haveincluded nuclear-weapon assembly and disas-sembly, and other national security activities,as well as analogous activities within theDepartment of Defense. In the area ofnuclear arms control, the RMF has seen fre-quent use by Livermore and visiting scien-tists from other national laboratories as anexperimental facility for the development ofverification and transparency technologies. Awide variety of items is available for experi-

The Radiation Measurement Facility atLawrence Livermore National Laboratory

Facilities


Adjacent to the bay on the level of the measurement platform is a large control roomwhere data collection and processing can take place. It also contains areas for mechani-cal and electrical bench-top work and small-group meetings. The platform and themeasurement region are easily observed from the control room. In this photo,observers at the 1997 Trilateral Initiative Technical Workshop are gathered in the con-trol room for refreshments and side conversations.

Not all transparency measurements made in the RMF are nuclear. Workers from PacificNorthwest National Laboratory perform early measurements using their electromagnet-ic induction method to determine the presence of plutonium in this AL-R8 fissile mater-ial storage container (see page 58).

menters, including unclassified uranium andplutonium items as well as nuclear weaponcomponents and NELAs.

The RMF has also hosted a number ofinternational experiments and demonstra-tions with technical experts from theRussian Federation and the InternationalAtomic Energy Agency (IAEA). In late 1994and 1996, the RMF was the facility for jointU.S.–Russia experiments to explore candi-date transparency technologies using unclas-sified sources of weapons-grade plutonium.In late 1997, the facility and the adjacent

Plutonium Facility were used to demonstratecandidate verification technologies for theTrilateral Initiative. In this latter demonstra-tion, 60 participants and observers, includ-ing delegations from the Russia and theIAEA, observed a variety of measurements ofplutonium attributes using unclassifiedsources of weapons-grade plutonium.

Don GoldmanLawrence Livermore National Laboratory


Overview to Arms Control Technology

The Atomic Nucleus

Matter is composed of atoms. Atomscomprise a tiny nucleus with a posi-tive electrical charge surrounded by

a cloud of negatively charged electrons. Thenucleus contains two types of particles ofroughly equal mass—neutrons and protons.Neutrons have no electrical charge and pro-tons have a positive electrical charge equal tothe electron charge. The number of protonsin the nucleus (called its atomic number, orZ) determines the chemical element. Forexample, all hydrogen atoms have one pro-ton, all iron atoms have 26 protons, and alluranium atoms have 92 protons. Except forthe very lightest elements, the nucleus hasabout twice as many neutrons as protons.The nuclei of all chemical elements can varyin their number of neutrons. These variationsare called isotopes.

Isotopes are written with a superscriptnumber indicating the total number of neu-trons and protons in the nucleus, followed bythe chemical letter abbreviation of the ele-ment that identifies its atomic number. 235Uis an important isotope of uranium (Z = 92)that has a total of 235 neutrons and protons.

RadioactivityFor a nucleus to remain stable, it must

have a proper balance of neutrons and pro-tons. A nucleus with too many or too fewneutrons is unstable and seeks stability byemitting particles—the process of radioac-tive decay, or radioactivity. All of the iso-topes of the heavy elements above bismuth(Z = 83) are radioactive.

A wide variety of subatomic particles isemitted during radioactive decay. Because oftheir ability to escape from the interior ofnuclear weapons or items in thick storagecontainers and be observed by external radi-ation detectors, two of these emissions arerelevant to arms control applications: neu-trons and gamma rays.

For heavy elements, spontaneous fissionis of considerable interest to arms control,particularly that of plutonium (Z = 94).Spontaneous fission is a decay process in

which the nucleus splits into two large frag-ments of nearly equal size accompanied bythe emission of several energetic neutrons.

Fission can also be induced. This common-ly occurs when a neutron emitted from a fis-sioning nucleus interacts with another nucle-us to induce another fission and release moreneutrons. The production of neutrons fromsuccessive fission processes of this kind iscalled neutron multiplication. Fission neu-trons are quite penetrating and can escapefrom plutonium in storage containers wherethey can be observed with a neutron detector.

Another form of radioactive decay com-mon among the heavy elements is the emis-sion of alpha particles. An alpha particle is atightly bound unit containing two neutronsand two protons. Alpha particles have shortranges and cannot escape from storage con-tainers but are of interest because the inter-actions of these particles with light impurityelements [called alpha-n or (α,n) reactions]also produce energetic neutrons.

All these neutrons are quite penetratingand can escape from the plutonium in anuclear weapon or component, or fromcontainers of bulk plutonium. Appropriatelyconstructed radiation detectors can deter-mine the amount of plutonium present andother attributes by counting the neutrons.

Another radioactive emission of particu-lar interest to arms control is gamma rays.Following radioactive decay, the resultingnucleus is usually left with excess energy.This energy is typically released through theemission of gamma rays. Gamma rays areelectromagnetic radiation, like x rays, buteven more penetrating. Moreover, they havesharply defined energies and the pattern ofgamma-ray emissions is unique for eachradioisotope—providing a nuclear signature.As seen in this issue of ACNT, gamma-raysignatures reveal a wealth of informationabout the materials emitting them. Thisincludes such attributes as isotopic compo-sition, the amount of time that has elapsedsince plutonium was last purified, and thepresence of chemical impurities.

About the Atomic Nucleus, Radioactivity,Fissile Materials, and Transparency


Overview to Arms Control Technology

Fissile MaterialsNuclear fission can be stimulated by flood-

ing heavy elements with neutrons. Fissilematerials are defined as those rich in heavynuclei that undergo nuclear fission whenexposed to slow neutrons. Materials with thisproperty are the essential ingredients ofnuclear explosives and therefore of keen inter-est to the arms control and nonproliferationcommunities. The two fissile materials of thegreatest interest are highly enriched uranium(HEU) and weapons-grade plutonium. In theU.S., HEU is defined as uranium enriched togreater than 20% in the fissile uranium iso-tope, 235U. The greatest interest is in HEUenriched to greater than 90% in 235U.Weapons-grade plutonium contains more than90% of the fissile isotope, 239Pu. Technicalmethods to identify the presence and quantityof fissile materials are essential components inproposed arms control regimes.

TransparencyEarly efforts at nuclear arms control

relied on “surrogates.” First, there were thetest ban treaties verified with satelliteimagery and seismic monitoring. Newertreaties, such as START I, focused on deliv-ery vehicles and were verified with satelliteimagery and direct observation (tape mea-sures and plumb bobs).

Even newer agreements involve nuclearwarheads as well as delivery vehicles andare not as easy to verify. One reason is thatnuclear weapons, their components, andbulk fissile material are relatively small andeasily moved or concealed. Another reasonis that details associated with the design ofnuclear weapons are among the most close-ly guarded secrets of nuclear-weapons states.As a result, the emphasis is now on “trans-parency measures” based on the inspectionof the weapon’s fissile materials, typically byexamination of their radiation signatures.Transparency measurements provide win-dows on the activities of the nuclear-weapons establishments of the treaty signa-tories. While the agreements are not verifi-able in the strict START I sense, inspection

experience with many items will build con-fidence over time that the signatories areliving up to the agreements (see figure.)

Transparency measurements based on radi-ation signatures are quite intrusive, as theycan potentially reveal aspects of a nuclearweapon’s design. With this in mind, novelapproaches to making these measurementsare necessary. These include robust measure-ment techniques that function regardless ofan item’s configuration and information bar-riers that protect classified information, yetallow the inspecting party to authenticatethat measurement results are genuine.

Thomas B. GosnellLawrence Livermore National Laboratory

All of theinspected

party'splutonium

Weapons-grade

plutonium

Weapons-grade plutonium

Correctage

Correctmass

Correct shape

Possibleweapons-

originmaterial

A hypothetical example of how a transparency regime could gain confidence that the material in a sealedstorage container is plutonium removed from a dismantled nuclear weapon. To do this, we can conduct aseries of measurements that considerably reduce the likelihood that the material came from anothersource. The first measurement, represented by the large blue circle, identifies the material in the containeras plutonium. A second measurement, represented by the inner dark blue circle, identifies the plutoniumas having weapons-grade isotopic abundances. To further increase confidence, three more measurementsare made. First, a significant mass of weapons-grade plutonium must be in the container—one or twograms won’t do (green circle). Second, the material must be old enough to have plausibly been in anuclear weapon—we’re not interested in newly produced plutonium (purple circle). Third, the plutoniummust be formed in the correct shape (yellow circle). The intersection of these three circles is the region ofpossible weapons-origin. Finally, if these measurements are extended to thousands of containers, the like-lihood that a significant quantity of this material is not from weapons is further significantly reduced.


Plutonium

The simplest method for detecting pluto-nium non-invasively uses an energyspectrum of the gamma rays emitted by

plutonium. The technology is both simpleand mature: a detector made of a scintillatingcrystal (commonly sodium iodide) is connect-ed to a photomultiplier that feeds signals toanalog electronics and a multichannel analy-zer. The result is a “low-resolution” spec-trum—many details of the photon energiesare washed out by the limitations of the scin-tillator. The analyzer in turn passes informa-tion to software that determines whether theenergies of gamma rays are consistent withthose of plutonium, again within the limita-tions of the low-resolution detector.

Commercially available instruments existfor a wide range of isotope-identificationfunctions, although most must be cus-tomized for plutonium detection. Oneexample is the RANGER-PLUS system, modi-fied to incorporate information-barrier fea-tures, used in the fall 1999 measurementtests at Pantex (see page 6). This instru-

ment, originally devel-oped by Los AlamosNational Laboratory, wastransferred to Quantrad, aprivate company.

This method is limitedin transparency regimes.Only the detection of plu-tonium is possible.

Quantitative information regarding mass,etc., is beyond the scope of the technique.Algorithms allow instruments to assert thatthe mass present has a lower bound, that is,greater than some value; however, that valuemay be much less than the actual amountpresent. Furthermore, the method does notspecify the isotopic composition of the pluto-nium, except in a few, restricted applications.

For quantitative estimates of mass, neu-tron methods are preferred, despite their rel-ative complexity and cost. To determine iso-topic composition, high-resolution gamma-ray spectroscopy is preferred, despite itslogistical difficulties (notably cryogenic sup-port). Finally, situations in which plutoni-um is shielded by high-Z materials betweenthe plutonium and detector pose problemsof data acquisition and analysis.

Research continues on detector materialsthat will improve the energy resolutionattainable with portable, room-temperatureequipment. The payoff is increased confi-dence that the material present is indeed plu-tonium, coupled with shorter counting timesand greater robustness in the face of shield-ing. DOE has supported research on cadmiumzinc telluride, a higher-resolution detectormaterial currently being incorporated into asuccessor to the RANGER-PLUS system.


Using Low-Resolution, Gamma-RaySpectroscopy To Detect the Presence of Plutonium

A RANGER-PLUS system (lower right)and its accessories in its rugged trans-port case. This system is a low-resolutionspectrometer that can detect andidentify plutonium.


Plutonium

Plutonium metal parts, as well as chemi-cal compounds, are often transferredand stored in stainless-steel containers.

These containers are about 5 centimetersthick. To identify the material in such con-tainers, it is sometimes necessary to deter-mine the isotopic content. A standard wayis to analyze the gamma rays escaping fromthe container. A gamma-ray spectrometeracquires a gamma-ray spectrum, which isthen analyzed with a computer program todetermine the isotopic composition. One ofthe most accurate programs is Multi-GroupAnalysis (MGA). Because MGA analyzes rela-tively low-energy gamma rays, its usefulnessis limited by the thickness of the containerenclosing the plutonium.

A 1.6-kilogram plutonium sample wasanalyzed with a commercially availabledetector to see how accurately and rapidlyMGA could measure the isotopes of plutoni-um stored in stainless-steel containers of dif-ferent thicknesses. The plutonium was mea-sured at varying distances (0–2 meters) andcount times (10 seconds–30 minutes). Todetermine the maximum allowable contain-er thickness, we measured a 0.4-gram pluto-nium source, with containers ranging from31.8 centimeters to 2.5 centimeters thick.

Plutonium isotopes can be quickly andaccurately determined for a large plutoniumsample inside of a 1.27-centimeter-thickstainless-steel container. Counting times aslow as three minutes were used to deter-mine the 240Pu/239Pu ratio to within 5%.

Plutonium AgeIt is sometimes necessary to know the age

of plutonium (how long ago the plutoniumwas chemically purified) to determine whenit was made, or when it was last chemicallypurified (for example, reprocessed reactorfuel). A signature of plutonium age is the241Am content. Freshly purified plutoniumhas no americium, but as the plutoniumages, the 241Am content increases in apredictable way.

The gamma rays from americium andplutonium penetrating the container canbe analyzed to determine the age. MGAwas designed to accurately count gammarays and this determines the plutoniumisotopic content.

Several commercial companies sellgamma-ray measurement systems that useMGA. We are currently verifying the abilityof two of these systems (from differentAmerican companies) to accurately deter-mine plutonium age. In our experimentswith “old” (27-year-old) plutonium, wehave determined that the age of plutoniumin stainless-steel containers as thick as 1.27centimeters can be accurately determined.

To verify the ability of MGA to accurate-ly determine the age of freshly purified plu-tonium, we are currently preparing such asample. We will periodically measure itover a period of months to verify the accu-racy of the age determined by MGA, as wellas the maximum allowable thickness ofstainless steel.

Rodney J. DouganLawrence Livermore National Laboratory

Measuring Plutonium Isotopes and Age with MGA

High-resolution gamma-rayspectrum of an unclassifieditem shows the spectral regionsfrom which data are acquiredfor the Pu300, Pu600, andPu900 analyses.


Plutonium

Developed especially for plutoniumtransparency, the Pu300, 600, and900 systems measure attributes of

classified plutonium items in heavy, closedstorage containers. They exploit higher ener-gy gamma-ray emissions from plutoniumthan are traditionally used in nuclear safe-guards—particularly for the important attrib-utes of plutonium age and weapons-qualityplutonium. The high-resolution spectrumfrom a plutonium item is rich with informa-tion and much can be learned about theitem that produced it. For transparency mea-surements, we therefore only acquire datafrom the narrow bands of the spectrum nec-essary to determine the attributes.

The Pu300, Pu600, and Pu900 systemsinclude gamma-ray detectors with high-energy resolution, data-acquisition electron-ics, simple computers for instrument con-trol and data analysis, and elements of aninformation barrier (see page 6). These sys-tems were integrated into the attribute mea-surement system for the recent FissileMaterial Transparency TechnologyDemonstration (FMTTD) (see page 14).

Determining plutonium ageThe key attribute measured by Pu300 is

age, defined as the amount of time elapsedsince the plutonium was chemically puri-fied. Age is based on the decay characteris-tics of 241Pu and its daughters, 237U and241Am. We use the highest energy region ofthe gamma-ray spectrum where a high-con-fidence age measurement can be made—between 325 and 350 keV.

Freshly separated plutonium contains sev-eral plutonium isotopes, including 241Pu butno 237U or 241Am. 241Pu is not stable anddecays through two paths. The alpha decaybranch goes to 237U, and the beta decaybranch goes to 241Am. Both the 237U and the241Am subsequently decay to two identicalstates in 237Np by gamma-ray emission,including two intense gamma rays with ener-gies between 325 and 350 keV (see figurebelow). The plutonium decay gamma rays,including gamma rays from 239Pu, are collect-ed with a high-purity germanium detectorand analyzed with the Pu300 code thatresolves the peaks from 241Am and 237U fromthe 239Pu peaks in the region. The number ofcounts in these peaks gives us the emission

Pu300, Pu600, and Pu900 Systems

106

105

104

103

102

101

0 100

Pu300—Pu age, presence

Pu600—weapons-quality Pu, presence

Pu900—absence of PuO2

200 300 400 500

Energy (keV)

Co

unts

/ch

ann

el

600 700 800 900 1000


Plutonium

rates of these gamma rays. The branchingdecay of 241Pu causes the levels that emit the332.4- and 335.4-keV gamma rays to be pop-ulated at different rates. Because these ratesare a well-known function of time, they allowus to uniquely determine the age.

Determining the presence of weapons-grade plutonium

The Pu600 method examines a narrowenergy region of the plutonium spectrumcontaining a complex multiplet of gamma-ray lines between 630–670 keV. Pu600 mea-sures the relative amounts of the isotopes240Pu and 239Pu. Because more than 99% ofthe mass of weapons-grade plutonium isdue to 240Pu and 239Pu, a low value (<0.1)of the 240Pu/239Pu ratio indicates the pres-ence of weapons-quality plutonium.

The Pu600 analysis uses a variant of theMGA code to determine peak areas in the630–670-keV energy region (see page 31).The 240Pu/239Pu ratio is proportional to theareas of the 240Pu peak at 642.5 keV and the239Pu peak at 646.0 keV.

Determining the presence of plutoniumDetermining the somewhat redundant

“presence of plutonium” attribute is a by-product of the Pu300 and Pu600 analyses.For the FMTTD, we required that the soft-ware determine the presence of 239Pu peaksat 345.0 keV from the Pu300 analysis and645.0 and 658.9 keV from the Pu600 analy-sis. To declare plutonium’s presence, werequired that all of these peaks exceed theunderlying continuum by at least five stan-dard deviations.

Determining the absence of plutonium oxide

The “absence of plutonium oxide (PuO2)”attribute is a surrogate for the truly desiredattribute—the “presence of plutoniummetal.” The consensus among several nation-al laboratories was that determining the pres-ence of plutonium metal in a sealed contain-er is not technically feasible. Instead, notingthat the most probable alternate form wouldbe PuO2, and that detecting the presence ofoxygen seemed possible, it was decided tosubstitute an “absence of PuO2” attributeusing the Pu900 system.

59.5

59.5

164.

616

4.6

164.

6

241Pu(14.35 y) β-(99.998+%)

241Am(432.2 y)

237U(6.75 d)

β-(100%)

α(0.00245%)

α(100%)

237Np(2.14 × 106 y)

59.5

64.8

64.8

64.8

335.

436

8.6

370.

9

267.

526

7.520

8.8

208.

8 332.

433

2.4

267.

520

8.8 33

2.4

160.

016

0.014

8.6

148.

610

3.7

103.

777

.177

.116

0.014

8.6

103.

777

.1

0

5

10

0.1 1 10 50Plutonium age (y)

333/

335-

keV

em

issi

on

rat

e

The age of plutonium can be determined by the relative emissionrates of the 332.4- and 335.4-keV gamma rays.

The branching decay of 241Pu shows the gamma-ray transitionsmeasured by the Pu300 method.

We focused initially on a 870.7-keVgamma-ray photopeak that is absent whenthe sample is a metal. The 870.7-keVgamma ray is emitted during de-excitationof the first excited state of 17O. It was ini-tially thought that the mechanism that pro-duces this excited state was due to alphaparticles from the decay of plutonium,interacting with oxygen by coulomb excita-tion, an inelastic process, 17O(α,α’). It waspointed out by workers at Pacific NorthwestNational Laboratory that another mecha-nism is possible—alpha particle reactions

with nitrogen impurities in the oxide,14N(α,p). Subsequent work, first at PacificNorthwest and then corroborated byLawrence Livermore, involving PuO2 sam-ples of varying degrees of chemical purifica-tion, indicates that the latter mechanisdominates. Nevertheless, the presence ofthe 870.7-keV peak unequivocally indicatesnon-metallic plutonium. Because the PuO2sample used in the FMTTD exhibited astrong 870.7-keV peak, it was decided, dueto time constraints, to use this indicator.

Meanwhile, measurements at LawrenceLivermore demonstrated a possible alterna-tive, the 2438.0- and 2788.8-keV peaks fromthe 18O(α,n)21Ne reaction. Unlike the870.7-keV peak, 21Ne appears to be unam-biguously due to oxygen. The 21Ne lines areweakly emitted, requiring care in the selec-tion of measurement geometry and the useof digital data-acquisition equipment toobtain a signal of adequate strength for anarms control regime. At publication time,the issues surrounding measurement of thepresence of PuO2 by gamma-ray spectrome-try were still unresolved.

Dan Archer, Thomas Gosnell, John Luke, and Les NakaeLawrence Livermore National Laboratory


Plutonium

239Pu240Pu 241Am

104

105

103

102

101

100

Co

unts

635 640 645 650 655 660 670665

The 630 to 670-keV region of the gamma-ray spectrum shows its resolution by nonlinear regression intoits isotopic constituents for the Pu600 method.

Neutron multiplicity countingwas demonstrated at a TrilateralInitiative Technical Workshop in1997. Participants included theRussian Federation and theInternational Atomic EnergyAgency as well as several DOEnational laboratories. This neu-tron multiplicity counter is oneof a pair developed to measureplutonium items in storagecontainers.


Plutonium

When oxygen is present in a sampleof plutonium, the alpha particlesemitted by the plutonium react

with the oxygen nuclei to produce neutrons.These neutrons can be detected by neutronmultiplicity counting, which measures theratio of these (α,n) neutrons to the neutronsspontaneously emitted by the plutonium.This ratio is called simply “alpha.” For pureplutonium metal, alpha is zero. If oxygen ispresent, alpha is non-zero. A near-zero alphameasurement indicates the “absence ofoxide.” A measurement of alpha will neverbe exactly zero because of the statisticalnature of neutron measurement.

A problem with using alpha to indicatethe absence of oxide is that other materialsalso cause excess neutrons to be produced.If elements of low atomic number (fluorine,boron, beryllium, magnesium, or chlorine)

are present in the plutonium metal, (α,n)neutrons are also produced, and alpha isnot zero even if no oxygen is present. Thus,using measurements of alpha to verify the“absence of oxide” can be ambiguous. Ifalpha is near zero, we can be confidentthere is no oxygen present. However, ifalpha is non-zero, oxygen may or may notbe present.

Greater confidence in the absence ofoxide is achieved by analyzing the gammarays emitted by the plutonium sample andrequiring that, in addition to alpha beingclose to zero, there is no measurablegamma-ray line attributable to the presenceof oxygen.

Diana LangnerLos Alamos National Laboratory

Absence of Oxide—Neutron Multiplicity Counting

Avery crude estimate of the plutoniummass in an object can be measured—subject to some extremely important

limitations—by simply counting the grossnumber of neutrons emitted by the object.Instruments such as the INF detector (seesidebar, page 9) or its Russian analog countneutrons at a fixed distance from the object.Following corrections for geometry anddetector efficiency, the count rate estimatesa plutonium mass based on the plutoniumisotopic composition (known or assumed)and the fact that the isotope 240Pu emitsapproximately 980 neutrons per gram persecond, owing to spontaneous fission.

Any mass estimate thus derived, however,must be considered with caution, becausephysics interferes with the direct relation-ship between the neutron count rate and240Pu mass. Detectors can only register the

neutrons escaping a object, which may con-tain neutron-absorbing materials, leading toan underestimate of the plutonium mass.

More significant effects produce overesti-mates of the mass; the most important areneutron multiplication (always presentwhen chain-reacting material is present inquantity) and emission of neutrons (pro-duced when plutonium is in intimate con-tact with light elements such as oxygen orberyllium). Neutrons are a particular prob-lem in measuring plutonium oxide, particu-larly impure material, in which singlescounting might overestimate the mass by asmuch as a factor of 10.

Finally, and perhaps most importantly,isotopic sources such as 252Cf also emit neu-trons that cannot be distinguished fromthose emitted by plutonium solely by sin-gle-neutron counting. Because of these con-cerns, singles counting cannot providequantitative information on plutoniummass, or even definitive proof of the pres-ence of plutonium, without corroborationby some other technique; the much morepowerful neutron-coincidence counting ispreferred for quantitative measurements.

A very simple form of singles countingwas demonstrated during the initial MutualReciprocal Inspections (MRIs) (see sidebar,page 9) exchanges, where the goal wasmerely to show that “a lot” of plutoniumwas present in a container. The instrumentused in that demonstration was the NAVI-2system, which incorporated a small neutrondetector and also a gamma-ray detector toprovide some evidence that the neutron-emitting material was indeed plutonium.This instrument has been enhanced consid-erably since the 1994 demonstrations. TheNAVI-2 is used today in applications wheregeneral confirmatory measurements and notdetailed mass information are required.



Plutonium

Vayacheslav Yanov of the Russian Research Institute of Pulsed Techniques (center) prepares tomake a plutonium mass estimate using a SRPS7 neutron detector during the 1994 joint experi-ments with Los Alamos and Lawrence Livermore National Laboratories.

Estimating Plutonium Mass via Singles Neutron Counting


Plutonium

Neutron multiplicity counting (NMC)is a rapid, nondestructive assaymethod to passively measure pluto-

nium. The International Atomic EnergyAgency (IAEA) uses NMC to measure pluto-nium in Japan and to measure excessweapons plutonium in the U.S. It is alsoused for domestic safeguards programs inthe U.S., Europe, and Russia.

Recently, NMC has been proposed fordetermining if the mass of a plutonium-bearing object is above or below a specifiedthreshold. This arms control use focuses onthe Trilateral Initiative, the PlutoniumProduction Reactor Agreement, and theMayak Transparency Initiative. In thesearms control regimes, classified weaponscomponents or plutonium materials withclassified isotopic compositions must beexamined. By making separate measure-ments of single neutron events and coinci-dence events that involve two and threeneutrons, the large measurement inaccura-cies associated with plutonium mass deter-mination from singles neutron counting areavoided (see page 36).

The major advantages of NMC for theseapplications include its accuracy, robustness,and calibration using unclassified referencematerials. Representative materials that wouldbe classified for these initiatives are notrequired for this measurement technique.Typically, an NMC instrument is character-ized using a series of 252Cf sources. Then, the

detector’s performance parameters to plutoni-um are adjusted using an unclassified pluto-nium standard. Provided that neither theneutronics of the sample packaging nor thedetector’s electronic configuration changessubstantially, the detector is calibrated “forlife.” For well-known detector designs, eventhe last step of measuring plutonium is avoid-ed, and Monte Carlo calculations can adjustthe detector’s performance parameters to plu-tonium. If sample packaging changes and thepackage geometry and material compositionare well known, calculations can also adjustdetector parameters for these changes.

A large counter was demonstrated to aRussian delegation during a TrilateralWorkshop at Lawrence Livermore NationalLaboratory in 1997. This detector measuredbulk plutonium in sample sizes up to andincluding a 30-gallon drum. The twin ofthis instrument at the Rocky FlatsEnvironmental Technology Site has beenused since 1995 by the IAEA to measureexcess U.S. weapons plutonium. Thiscounter has also been used in a series ofexperimental tests on U.S. weapons compo-nents. Both of these instruments were cali-brated entirely with unclassified materials.The components measurements yielded themass of the plutonium accurately to about6% in 30 minutes.

Diana G. LangnerLos Alamos National Laboratory

Measuring Plutonium Mass by Neutron Multiplicity Counting

Experimental test measurementsof plutonium-bearing weaponscomponents using neutron multi-plicity counting at the Rocky FlatsEnvironmental Technology Site.


Plutonium

To confirm that inspected items areauthentic, some arms control agree-ments may require measurements of

nuclear weapons and their components.Inspected items should exhibit two chosenweapon attributes: that the mass of plutoni-um exceeds a declared threshold and thatthe isotopic composition is consistent withweapons-grade material. A Minimum–MassEstimate (MME) method confirms plutoni-um mass threshold and isotopic composi-tion using only a high-purity germaniumdetector. The masses of all gamma ray-emit-ting isotopes are estimated by fitting fea-tures in the spectrum associated with inten-sities of the gamma-ray peaks and low-anglescattering. The MME method provides highconfidence that the amount of plutonium isat least as great as the MME, but the actualamount of material may be substantiallygreater if the plutonium is thick or if theshielding is nonuniform. Because features in

high-resolution spectra are unique to pluto-nium, the spectral characteristics cannot bereproduced by substituting other materials.

The exact computation of the intensitydistribution of radiation emitted by anuclear weapon is a complex problem thatrequires defining the source geometry. Thiscreates an impasse because the plutoniummass cannot be computed without knowingclassified information. Therefore, ratherthan attempting to replicate the actualsource, the MME method describes a config-uration that could produce the spectrumusing the minimum quantity of plutonium.In the hypothetical minimum-mass model,plutonium self-attenuation is ignored andintervening materials are assumed to beuniform. Given these assumptions, comput-ing the intensities of gamma rays and low-angle scattered photons is greatly simplified.The process of fitting the spectrum usingnonlinear regression estimates the masses of

Minimum-Mass Estimates of Plutonium

Based on a minimum mass esti-mate model, the gamma-rayspectrum recorded for a400–gram plutonium plate iscompared to a computed spec-trum. The filled regions repre-sent the contributions from eachof the isotopes included in themodel. The gray region repre-sents an empirical continuum.The yellow region representsphotons that scatter at lowangles relative to the incidentphoton trajectories. Note thatthe region between 470 keVand 590 keV is not represented,producing a discontinuity atabout 470 keV.

400 620 700

239Pu

241Am

240Pu

238Pu

232U

238U

226Ra

scatter

Energy (keV)

Co

unts

/ k

eV

105

105

105

105

105

360320 440 660 740 780

Plutonium


all the isotopes that emit gamma rays intwo energy regions: 315 to 470 keV and 590to 780 keV. These isotopes include 238Pu,239Pu, 240Pu, and 241Am.

Among the sources evaluated using theMME approach was a 400-gram, 2.3-mil-limeter-thick plate of weapons-grade pluto-nium. The plate is surrounded by aluminumcladding, a steel drum, and various thick-nesses of lead. Intervening materials havelittle impact on the mass estimates. The plotcompares one measurement to the comput-ed spectrum based on the MME model. TheMME for 239Pu is about 90% of the actualmass for the measurements of the plutoni-um plate. The ratios of masses of the otherisotopes to 239Pu are approximately correct,though the relative uncertainty for 238Pu islarge due to statistical uncertainties becauseonly 0.05 grams of this isotope were pre-sent. Despite the simplifying assumptions,the MME method is sufficiently robust to

produce good fits to spectra recorded for alarge range of nuclear weapons and theircomponents.

A limitation of the MME method is thatthe spectrum must exhibit well-definedpeaks for the isotopes in plutonium. If thegamma rays from plutonium are highlyattenuated and if there is a strong continu-um such as that produced by Bremsstrah-lung radiation, it may not be possible todetermine either peak intensities or the con-tinuum associated with low-angle scatter-ing. Masses are also underestimated signifi-cantly when the plutonium thicknessexceeds several millimeters.

Dean J. MitchellSandia National Laboratories


Plutonium

Under some circumstances, it may beimportant to know if the object in astorage container is cylindrically

symmetric. We test for cylindrical symmetryby looking for an isotropic neutron radia-tion field emitted by a plutonium object ina sealed storage container. Vitaliy Dubininof the All-Russian Scientific ResearchInstitute of Experimental Physics (VNIIEF)suggested this method during the MutualReciprocal Inspections discussions inMoscow in 1996 (see sidebar, page 9).Shortly after, the method was tested in jointU.S.–Russia experiments at LawrenceLivermore National Laboratory.

For these experiments, neutron countsfrom unclassified plutonium objects in sealedstorage containers were recorded followingincremental rotations of 15°. Ideally, if theitem is cylindrically symmetrical, the neu-tron count will be equal at each rotationalposition. The 1996 experiments employedfree-field measurements conducted on a low-scatter platform in the Radiation Measure-ment Facility (see page 26).

For the recent Fissile MaterialTransparency Technology Demonstration(FMTTD), held at Los Alamos NationalLaboratory, a number of different plutoni-um attributes needed to be measured simul-taneously (see page 14). One of these attrib-utes was the mass of the object in a storagecontainer, measured by a neutron multiplic-ity counter. It was possible to conduct the

symmetry measurements simultaneously bytapping the neutron counts from the eight,equally spaced neutron detector banks inthe multiplicity counter.

Another requirement for the FMTTD wasthat the measurements needed to be madebehind an information barrier (see page 6).As a consequence, data acquisition andanalysis needed to be done by an unattend-ed computer. Data from the eight scalerswere automatically adjusted to reflect smallefficiency differences in the eight detectors.The symmetry attribute was determined bya simple analysis of the adjusted net (back-ground subtracted) detector counts to findthe one detector that deviated the mostfrom the average value of the adjusted netcounts from all of the detectors. Theabsolute fractional deviation, s, about theaverage was computed.

The values of s were compared to an arbi-trary threshold value chosen specifically forthe FMTTD. To be declared asymmetric, thevalue of s had to exceed 0.15. When thisoccurred, a red light indicated a failure ofthe symmetry attribute; otherwise, a greenlight indicated adequate symmetry.


Diana C. LangnerLos Alamos National Laboratory

Symmetry Measurements of Plutonium Objects

During joint experiments in 1996, U.S. andRussian detectors measured unclassified plu-tonium objects in storage containers. Total neutron measurements were made with aRussian SRPS7 detector (white box) and aU.S. SNAP-2 detector (blue box).


Plutonium

180º

90º

0º

270º0.60.6 0.80.8 1.21.210.6 0.8 1.21

180º

90º

0º

270º0.60.6 0.80.8 1.21.210.6 0.8 1.21

(left) Polar plot of the neutron counts recorded from a plutonium sphere in an AT400R container during the 1996 joint experiments. The cir-cular pattern indicates the presence of a cylindrically symmetric object in the container. (right) This polar plot, produced from counts recordedfrom a thick plutonium disk, shows that the neutron field is anisotropic, indicating asymmetry.

Block diagram of the neutron symmetry measurement made during the FMTTD. The eight outputs fromthe neutron multiplicity counter are recorded on an eight-input scaler and then analyzed by the PC-104single-board computer.

Pulse processing electronics

Symmetry analyzer

BusNMCMulti-inputscaler

PC/104SBC

Using unclassified sources, a simple detector measured the gamma-ray flux at a number of positions outside the container. The differentreadings generated an image. More advanced instruments can per-form the same inspection at a distance of several feet in much short-er time intervals (well under an hour.)


Plutonium

The design of a nuclear weaponrequires careful choice of the shape ofthe nuclear materials used to generate

the explosion. As such, this shape is animportant attribute to verify that materialin a disassembly stream originates fromweapons. The shape is so much a part ofthe design that the details of the shape, i.e.,exact dimensions, are classified.Nevertheless, if we could verify that the fis-sile material is of approximately the correctdimensions, this would strongly indicatethat the component originates from a dis-assembled weapon. Such a measurementcan be made remotely on plutonium even ifit is in a sealed, opaque container.

To measure shape, we take advantage ofthe fact that plutonium, like other fissilematerials, emits gamma radiation character-istic to that material. Gamma radiation isnothing more than high-energy light thatcan penetrate through a significant amountof matter. Plutonium glows with this radia-tion, much like a light bulb, with the differ-ence being that the gamma rays will contin-ue on through the walls of a sealed contain-er as if the plutonium were in a clear vessel.With a suitable instrument, we can capturethis “light” and make an image of the plu-tonium (see image). Although this image isat somewhat worse resolution than wemight produce with a camera, it is sufficientto verify that the radioactive material in thecontainer has the correct shape to meettransparency requirements, and—based onthe spectral information—that it is thematerial claimed.

Classification concerns are met in twoways. The image resolution of such aninstrument (number of centimeters perpixel) can be adjusted in an easily verifiablefashion, so that details of the plutoniumpiece below a certain size are not visible. Or,the inspection can be automated so that noimage is ever displayed. Here, a computerroutine analyzes the data behind an infor-mation barrier, responding with a “redlight” or “green light.”

Klaus-Peter ZiockLawrence Livermore National Laboratory

Gamma-Ray Imaging To Determine Plutonium Shape

Computer calculation of the dif-ferentiation of point and sphericalsources. The collimator is 40 mmlong and 3.175 mm wide.


Plutonium

Aunique, radiation-sensitive film com-bined with the property of opticallystimulated luminescence (OSL) can

generate a low-resolution, two-dimensionalimage of a nuclear weapon component in astorage container. It can determine thepresence of nuclear materials and definethe attribute of a distributed versus pointradiation source. The film is read using areader that limits the resolution of theimages to no finer than 1 centimeter-by-1 centimeter pixels.

After exposure to a radiation field, theinternal crystal structure of OSL materials isdisplaced, making the OSL materials sensi-tive to light stimulation at specific frequen-cies. When stimulated by green light, thematerial emits blue light directly propor-tional to the radiation-field exposure (seeimage). A specially constructed reader scansthe OSL film with green light, producingblue emitted light.

The magnitude of the blue light is pro-portional to the radiation intensity. Light-emitting diodes excite the OSL film, illumi-nating a 1 centimeter-by-1 centimeter area.This large illumination area limits the reso-lution of the detection system to no betterthan 1 centimeter-by-1 centimeter. Unlikeordinary x-ray film, the radiation patterns

generated by the OSL film cannot be seenwith the human eye. It takes the OSL readerto make the image visible. The OSL film isreusable, can be erased, and does not gener-ate chemical waste, as does ordinary radi-ographic film.

To identify the presence of nuclearweapons components within containers, theOSL film can discern the distributed-versus-point source attribute. Computer calcula-tions of the OSL film placed behind a tincollimator have demonstrated the ability todistinguish a point source from a distributedsource. The tin collimator, if spaced everyone centimeter to collimate the intrinsicradiation, measures the extent of the source.Note the clearly different patterns generatedby the two types of radiation sources.

Monitoring warhead materials and com-ponents during transport and warhead dis-mantlement are envisioned. OSL filmaccomplishes this without the intrusivenessinherent to conventional x-ray film radiog-raphy, without generating an intrusive,high-resolution image, and without generat-ing a toxic waste stream.

Steve D. MillerPacific Northwest National Laboratory

Autoradiography Adaptation UsingOptically Stimulated Luminescence

0

5

10

15

20

25

0 5 10 15 20

Inte

rval

Co

unt

Rel

ativ

e to

Mim

imum

Co

unt

Collimator Interval Number

Point SourceSpherical Source


Plutonium

The Nuclear Materials IdentificationSystem (NMIS) was developed jointlyby Oak Ridge National Laboratory and

the Y-12 Plant for nuclear-material controland accountability. NMIS has been usedwith active neutron interrogation for bothhighly enriched uranium (HEU) and pluto-nium, and with passive neutron interroga-tion (no external source) for plutonium.

In active techniques, fissile material—stimulated by an external neutron source—fissions, producing neutrons and gammarays. The time distribution of particles leav-ing the fissile material can be measuredwith respect to the source emission in avariety of ways and with a variety of accel-erator and radioactive sources.

The data from interrogating nuclearweapons and components can be used intwo ways: template-matching and attribute

estimation. Template-matching comparesradiation signatures with known referencesignatures. For treaty applications, authenti-cating the reference signatures along withstoring and retrieving templates may be dif-ficult. Attribute estimation, on the otherhand, determines the fissile mass and otherproperties from various features of the radi-ation signatures and does not store radia-tion signatures. It does require calibration,which can be repeated as necessary.

NMIS is now used to verify weaponscomponents received and stored at Y-12 bytemplate-matching. NMIS also estimatestwo attributes, fissile mass and enrichment,for HEU metal. NMIS employs a 252Cfsource of low intensity (<5 × 106

neutrons/second) such that the dose at onemeter is approximately twice that of a com-mercial airliner at cruising altitude. Such a

Attributes and Templates from ActiveMeasurements with NMIS

A typical active measurement of a fully assembled weapon at the Pantex Plant. The radioactive source, 252Cfin an ionization chamber, is on the right and four (at least one is required) detectors are on the left.Radiation emanating from the 252Cf source is transmitted through the weapon, scattered by the weapon, andinduces fission in the weapon with the resulting radiation from all three processes reaching the detectors.

SourceDetectors

Plutonium


source presents no significant safety con-cerns, either for personnel or nuclear-explosive safety, and has been approved foruse at the Pantex Plant on fully assembledweapons systems. The same NMIS tech-nique has also been used for HEU metal atthe Y-12 Plant, where both the fissile massand the enrichment were measured to ±2%.

Presently, three systems are routinely usedat Y-12 to confirm or verify the weaponscomponents in containers. This method wasnon-intrusively demonstrated to Russian vis-itors in 1997 and 1998. One such system is

now used at the All-Russian ScientificResearch Institute of Experimental Physics(VNIIEF) in Sarov, Russia, and another hasbeen shipped to the All-Russian ScientificResearch Institute of Technical Physics(VNIITF) in Snezhinsk, Russia. Recent pas-sive measurements were completed withplutonium metal (1.77 wt%) at VNIIEF,showing that NMIS could estimate massand thickness of the metal.

John T. Mihalczo and J. K. MattinglyOak Ridge National Laboratory

The equipment setup for verifying HEU metal at the Y-12 Plant in Oak Ridge,Tennessee. The 252Cf source is located near the part. The uranium mass and enrich-ment of the HEU metal in birdcages were determined to within ±2%.

Russian visitors watch a demonstration of the active interrogation technique. The 252Cfsource and detectors are located around a container with a weapon component inside.


Uranium

Highly enriched uranium (HEU) is oneof two fissile materials incorporatedin nuclear weapons. During the Cold

War, hundreds of metric tons of HEU wereproduced by the U.S., Soviet Union, andother nuclear-weapons states. The ability todetect HEU in nuclear weapons and theirdismantled components is viewed by theU.S. policy community as a potentiallyimportant transparency measure.

Passive detection methods exploit signa-tures intrinsic to the undisturbed material.To protect classified information, measure-ments are made outside the weapon or stor-age container. Nuclear weapons and compo-nents in their storage containers are large,dense, and nonhomogeneous. Signaturesmust be sufficiently penetrating to escapefrom the interior of the weapon or containerand reach a detector. Signatures must also besufficiently intense to complete an inspec-tion measurement in a reasonable period oftime. For HEU, the only signature thatapproaches these criteria is from gamma raysemitted by the radioactive decay of uraniumisotopes. Unfortunately, the signature of235U is so weakly penetrating that simplydetecting shielded HEU—let alone quantify-ing it—is a task that ranges from straightfor-ward to nearly impossible.

Even if 235U is detected, its presence alonedoes not mean the uranium is HEU. Todetermine this, we must have some indica-tion of the enrichment. The other dominantisotope of HEU is 238U. Knowing the concen-tration of both isotopes provides an estimateof uranium enrichment. However, even if235U is detected, the dominant gamma raysfrom both isotopes are sufficiently well sepa-rated in energy (186 keV for 235U and 1,001keV for 238U) that unknown relative attenua-tion of these gamma rays within the urani-um items and through their storage contain-ers precludes knowing their true relativeemission intensities. An exception is the“enrichment meter” method that examinesthe 186-keV peak and the adjacent continu-um to determine uranium enrichment (seepage 52). The method requires calibrationagainst known standards, a condition unlike-ly to occur in arms control scenarios ofincreasing interest. These scenarios includeheavily shielded HEU so that methodsdetecting the 186-keV gamma ray are notapplicable.

Because determining the presence ofshielded HEU by measuring its key isotopesis intractable in some arms control settings,an indirect alternative signature is beingexplored—detecting the impurity isotope232U. 232U does not occur in nature but isintroduced into HEU as a result of repro-cessing uranium reactor fuel. In the 1960s,uranium separated from irradiated plutoni-um production reactor fuel was introducedinto U.S. gaseous-diffusion plants to beenriched. As a result, trace quantities of232U were entrained in the gaseous-diffu-sion cascades where they remain today, con-taminating new feed stock as it is beingintroduced into the cascade. 232U is foundtypically at the 100–200 parts per trillion(ppt) level in U.S. HEU. We believe that asimilar circumstance occurred in the SovietUnion. Evidence indicates that, during theenrichment process, 232U is preferentiallyswept into the light isotope fraction thatbecomes HEU and amounts too small tomeasure go into the heavy isotope fraction

Determining the Presence of HEU with Passive Detection Methods

High-resolution gamma-rayspectrum of a 2.2-kilogramspherical source of uraniumenriched to 93% in 235U. The232U content is 100 parts pertrillion. The red, orange, andyellow areas indicate where themost prominent peaks are locat-ed for 235U, 238U, and 232U,respectively.

106

105

104

103

102

Energy (keV)0 500 1000 1500 2000 2500 3000

Net

co

unts

101

100

235U

232U

238U

10–1


Uranium

that becomes depleted uranium. Therefore,the presence of 232U in uranium is consis-tent with that uranium being HEU.

232U is part of the collateral radioactivedecay series associated with the thoriumdecay series. The thorium series is one ofthree sources of natural gamma-ray back-ground radiation. This series begins with232Th and decays through a series ofradioactive daughters including 208Tl. Anumber of emissions are associated withthis decay series, but the most distinctive isa highly penetrating 2,614-keV gamma rayemitted following the beta decay of 208Tl.Because 232U enters the thorium series at228Th, it too exhibits the 2,614-keV gammaray as a signature. Because of the relativelyshort half-life of 232U and the short half-lives of its daughters, it is readily observablein a gamma-ray spectrum. At the 100-pptlevel, the 2,614-keV peak is of comparableheight to the 1,001-keV peak from 238U in93% enriched uranium.

Two difficulties must be overcome indetermining the presence of HEU by detect-ing 232U. First, gamma-ray emissions from232U are relatively weak, requiring largedetectors and possibly longer measurementtimes than normally desirable. In the unlike-ly event that a more satisfactory passivemeans of detecting shielded HEU is found,arms control regimes requiring the detectionof HEU must account for this difficulty. Thesecond difficulty is that the salient featuresof the 232U signature, notably its associationwith the decay of 208Tl and its 2,614-keVgamma ray, are not unique to 232U.

The signature associated with the decayof 228Th and all of its daughters, including208Tl, is found in natural background radia-tion due to traces of thorium ubiquitous inthe earth’s crust. Discrimination againstbackground 2,614-keV gamma rays can belargely accomplished by massive shieldsaround the detector and behind the objectunder inspection. Another source of the2,614-keV signature is weapons-grade pluto-nium. During the creation of plutonium, atrace quantity of the impurity isotope 236Pu

is produced which decays to 232U andremains in the plutonium. Arms controlregimes must consider this possibility, but itmay be of small consequence, because inthis case, the presence of the 236Pu signa-ture is evidence of the presence of a fissilematerial. The final concern is that becauseboth natural thorium and depleted uraniumare plentiful and relatively inexpensive,they could be placed in the sealed containerto spoof a measurement. The naturallyoccurring thorium chain begins with thevery long-lived 232Th, which decays to228Ra then to 228Ac before reaching 228Th.A telltale clue that natural thorium is pre-sent is a cluster of gamma rays emitted by228Ac in the neighborhood of 900 keV witha 911-keV line being the most intense.

A simple measurement technique wouldbe to use a high-resolution gamma-raydetector to detect the penetrating 1,001-keVline from 238U to confirm the presence ofuranium (but not HEU), the 2,614-keV line(consistent with the presence of HEU orpossibly weapons-grade plutonium), andthe absence of a line at 911 keV to ensurethat the 2,614-keV line is associated withfissile material. Using the same measure-ment, determining the absence of a gammaray at 414 keV builds additional confidencethat the 2,614-keV line is associated withHEU rather than weapons-grade plutonium,which might be desirable in some armscontrol regimes.


The naturally occurringradioactive-decay series ofthorium is indicated in blue.The prominent gamma ray at2,614-keV (see figure on oppo-site page) is emitted due to thepresence of 232U from a collat-eral decay series that enters thethorium series at 228Th. Thisseries also includes 236Pu.

232U72 y

232Th1.4×1010 y

228Ra6.7 y

220Rn55 s

216Po0.16 s

212Po3.0×10–7 s

212Pb11 h

208Tl3.1 m

208Pbstable

212Bi61 m

224Ra3.6 d

αβ–

228Ac6.1 h

228Th1.9 y

236Pu2.9 y

34%

66%


Uranium

Fissile materials in shielded configura-tions are difficult to detect and charac-terize through passive measurements. In

some cases, actively interrogating thesematerials with neutrons or energetic pho-tons determines some properties of suchmaterials. Active techniques may providereliable ways to determine the presence ofhighly enriched uranium (HEU) and otherattributes for arms control initiatives. As inpassive methods, an information barrier willlikely be required to protect sensitive designinformation (see page 6). A principal R&Dgoal is identifying signatures that can serveas attributes capable of being verified withunclassified sources rather than using tem-plates which require a “trusted” classifiedobject to verify the measurement.

In an approach being examined at LosAlamos National Laboratory, an object isinterrogated with pulses of high-energyphotons (up to ~10 MeV) of sufficient ener-gy and intensity to produce neutrons fromphotofission or (γ,n) reactions in the fissilematerial. The resulting neutrons theninduce fission chains in the material.Neutron events detected in a high-efficiencydetector are time-tagged and analyzed todetermine a correlation signature. This sig-nature is a measure of the multiplication inthe assembly and thus could discriminateHEU from other materials. Electrons fromlinac or betatron accelerators striking ahigh-density (high Z) target produce theenergetic photons.

A related technique has been developedby Idaho National Engineering &Environmental Laboratory in which theelectron energy is varied from 8–12 MeV toproduce a variety of interrogating photonspectra. Characteristics of the resultinggamma rays and neutrons are measured asa function of the interrogation energy. Theresulting data provides a signature uniqueto a particular material. Results indicate apossible complementary photonuclearinspection method that uses electron accel-

erators producing less than 6-MeV electronsby relying on the fissioning properties ofHEU.

Another approach involves interrogationwith a pulse of deuterium-deuterium (d-d)or deuterium-tritium (d-t) reaction-generat-ed neutrons and measurement of the result-ing neutron intensity as a function of time(the differential die-away curve) inside amoderating cavity containing the material.This technique was originally developed atLos Alamos for waste assay and morerecently has been applied to monitoringpackages for the presence of special nuclearmaterials. The detection and analysis tech-nology is well developed for these applica-tions. Current work focuses on determiningsignatures from weapon components anddeveloping high-flux, long-lived neutrongenerators. The d-d reaction has a lowercross section and thus an inherent lowerflux for a given ion current. On the otherhand, long-life d-d generators can be devel-oped because the target deuterium is easilyreplenished and no tritium handling isneeded. Efforts to develop a high-currention source that can lead to a high-intensityd-d generator are underway at LawrenceBerkeley National Laboratory.

Another technique being studied atLawrence Livermore National Laboratoryemploys an accelerator-based neutron gen-erator to look above and below the 238U fis-sion threshold at ~1 MeV to determine thepresence of HEU. To detect the neutronsfrom the induced fission of uranium, we arelooking at conventional scintillation detec-tors as well as thorium fission chambers.Thorium fission chambers have the advan-tage of being insensitive to gamma rays andsensitive only to neutrons above 1 MeV.These advantages make their use a type of“information barrier,” which would be help-ful for transparency measurements. Newforms of thorium fission chambers are beingdeveloped to greatly enhance their intrinsicefficiency.

Active Interrogation for Monitoring HEU

Uranium


Major considerations in active approach-es are personnel safety from intense interro-gating radiation sources, nuclear-explosivesafety if weapons are being interrogated,and operational effects that might includeseparate facilities and measurement schemeswhich are significantly more complex thanpassive methods currently being considered.In summary, active approaches may offerthe only high-confidence means of meetingpotential HEU monitoring requirements,but they will be more expensive and com-plex and have a greater operational impactthan passive measures currently being con-sidered for verifying plutonium.

Robert ScarlettLos Alamos National Laboratory

James JonesIdaho National Engineering and Environmental Laboratory

Arden DouganLawrence Livermore National Laboratory

The Active Interrogation Package Monitor can detect the presence of special nuclear materials in a fewseconds even when the material is heavily shielded.

An inspection or verification technology for highly enriched uranium (HEU) stored in containers at a storage facility. The system uses a transportable, electron accelerator and a neutron detection system. The technology can inspect stored material and containers entering or leaving the facility.


Uranium

The Highly Enriched Uranium (HEU)Purchase Agreement between the U.S.and Russia provides for monitoring

the blending of HEU (500 metric tons) withlow-enriched uranium (LEU) to producecommercial reactor-grade material for theU.S. (see page 10). The Blend-DownMonitoring System (BDMS) was developedby DOE for the Russian facilities. It incorpo-rates the fissile mass flow monitor devel-oped by Oak Ridge National Laboratory andthe 235U isotopic enrichment method devel-oped by Los Alamos National Laboratory(see next page).

The system measures the flow rate of fis-sile material in process pipes, tracing the fis-sile material from the HEU leg to the LEUleg. The mass flow monitor induces fissionsin the fissile material and detects thedelayed gamma rays emitted by fission frag-ments at a detector downstream. Theinduced fissions are modulated using a neu-tron-absorbing shutter to create a time-dependent signature detected by the down-stream detectors. The mass flow monitordetermines the flow rate by measuring twothings: (1) the time required for the fissionfragments to travel along a given length ofpipe (inversely proportional to the fissile-material flow velocity), and (2) an ampli-tude measurement proportional to the fis-sile concentration (in grams of 235U per

unit length of pipe). Fissile flow is tracedthrough a blending tee by detecting time-modulated fission fragments in the LEUstream at a detector downstream of theblending point produced by the neutron-source modulation in the HEU stream.

The enrichment monitor, installed down-stream from the mass flow monitor, usesgamma-ray spectrometry to determine theenrichment. The BMDS confirms mass flowand traces fissile material. It is self-con-tained and fully automated, designed forunattended operation.

The BDMS has been installed and wassuccessfully demonstrated in the PaducahGaseous Diffusion Plant to a team ofRussian experts in 1998. In these tests, theenrichment varied from 1.5% down to1.1%. It has successfully operated in theUral Electrochemical Integrated Plant (UEIP)at Novouralsk in Russia, which has one unitoperating. Another monitoring system hasbeen shipped to the Electrochemical Plantat Zelegnogorsk for future installation.

John Mihalczo, James Mullens, Jose March-Leuba,and Taner UckanOak Ridge National Laboratory

Blend-Down Monitoring System for HEU

One leg of blending tee: Agamma-ray spectrometerusing a 252Cf source measuresthe 186-keV gamma ray from235U to determine the 235Ucontent of the HEU gas. It alsomeasures the 122-keV gammarays from a 57Co source toobtain the total uranium inthe gas. Both measurementsdetermine the enrichment ofthe product.

Blending point HEU57Co

252CfBDMS

BDMS

LEU

LEUproduct

Flow sourcemodulator

Enrichmentdetector

Flowdetectors

Blend-Down Monitoring System (BDMS)


Uranium

In February 1993, the United States andthe Russian Federation signed a bilateralAgreement for the U.S. to purchase low-

enriched uranium (LEU) derived from highlyenriched uranium (HEU) removed from dis-mantled Russian nuclear weapons. TheAgreement calls for the establishment oftransparency measures that provide both par-ties with confidence that the nuclear non-proliferation objectives of the Agreement arebeing achieved. The U.S. has the right toinstall non-intrusive, nondestructive assayinstruments to independently and continu-ously monitor the 235U enrichment at theblend point (see previous page).

Los Alamos National Laboratory devel-oped a detector to watch the enrichment ofuranium–hexafluoride (UF6) gas. The UF6 inthe HEU leg, at approximately 90% enrich-ment, mixes with 1.5% LEU blend stock toproduce LEU product in the 3–5% range.

The enrichment monitor measures theratio of 235U to the total uranium. Sodiumiodide (NaI) is the photon detector. The iso-tope 235U emits a prominent gamma raywith an energy of 186 keV. The count rateof the 186-keV gamma ray depends on thenumber of 235U atoms in the gas, which inturn depends on the uranium enrichmentand the gas pressure.

To measure the total amount of uraniumin the gas, we use a technique calledgamma-ray transmission. A 57Co gamma-ray source is mounted on the pipe oppositethe detector. This source has a prominentgamma ray with an energy of 122 keV. TheNaI detector measures simultaneously the186-keV count rate and the 122-keV countrate. These two quantities are first measuredwith the pipe empty of process gas, thenwith UF6 gas present. The empty pipe mea-surement determines the 186-keV countrate for the room background from nearbypipes and uranium deposits on the pipeinterior. The difference between the 186-keV count rates in these two measurementsdetermines the 235U signal originating inthe process gas.

The change in the 122-keV count rate inthese two measurements determines thetotal amount of uranium present in the gas.Combining the 186-keV measurement withthe 122-keV measurement gives a value ofthe enrichment of the UF6 process gas.

Phil KerrLos Alamos National Laboratory

Blend-Down Enrichment Monitor for HEU

The Ural ElectrochemicalIntegrated Plant is located inNovouralsk, Russia, where a per-manent office supports DOE’stransparency activity.


Uranium

Since January 1997, the HEUTransparency Implementation Programhas used nondestructive assay (NDA)

equipment to determine the 235U enrich-ment of highly enriched uranium (HEU) incontainers. Ten portable NDA systems arecurrently deployed at the four Russian sitesthat process material covered by the trans-parency agreements (see page 10). Theequipment measures several forms of urani-um, including metal components, metalshavings, uranium oxide, and uraniumhexafluoride.

The system measures the 235U enrich-ment by using an enrichment meter. Inthis method, the enrichment of the sampleis proportional to the rate of the 186-keVgamma rays emitted by 235U. This methodis valid for measuring the enrichment ofbulk uranium samples that are homoge-neous and large enough to fill the view ofthe gamma-ray detector with an “infinitethickness” of uranium. The gamma-raydetector views the sample through a colli-mator made of dense material, restrictingthe detector’s field of view so that reason-ably sized samples can fulfill the require-ments of the enrichment meter. “Infinitethickness” is defined as that amount ofmaterial that reduces the intensity of the186-keV gamma ray by a factor of onehundred. For uranium metal, this thicknessis about 3 millimeters; for solid uraniumhexafluoride, 1.4 centimeters. The uraniumsamples measured in the HEUTransparency Implementation Project arealways large enough to satisfy this “infinitethickness” condition.

The portable NDA system is composed ofcommercially available products: a collimat-ed NaI gamma-ray detector, a CanberraInspector, and a laptop computer. Thegamma-ray detector is a 1 inch-by-1 inchNaI crystal coupled to a photo-multipliertube. The signals from the detector areprocessed by electronic components in theCanberra Inspector unit. A laptop computercontrols the system and allows the operatorto input the necessary sample parameters,e.g., container-wall thickness and materialtype. The computer also analyzes thegamma-ray spectrum created by theInspector and then calculates and displaysthe measured enrichment.

Daniel DecmanLawrence Livermore National Laboratory

Portable Equipment for UraniumEnrichment Measurements

The portable NDA equipment used for measuring the 235U enrichment of uranium in containers.


A comparison of measured ura-nium enrichment with declaredenrichment for uranium sam-ples. The red squares are low-enriched uranium sources to cal-ibrate the system. The blue tri-angles are declared values ofhighly enriched uranium.

Uranium

We have developed a method todetermine the uranium enrich-ment of a sample in a container.

The sample can be in any chemical form,either an oxide or a hexafluoride. In addi-tion, the sample can be in any kind ofcontainer. The system uses a high-puritygermanium gamma-ray detector, aCanberra InSpector data-acquisitionsystem, and a laptop computer.

The collimator for the gamma-ray detec-tor is designed so that the field of view isfilled for all measurements. The softwarecorrects for the attenuation of the containerand the self-attenuation of the sample. Thesoftware requires a rough energy calibrationand an enrichment calibration using NISTuranium-oxide standards. The system doesnot require that the enrichment calibrationbe performed with attenuators, which is agreat leap forward from previous methods.We have tested this system on a wide vari-ety of samples in different forms and in dif-ferent types of containers and found it to bevery robust.

This method works very well, as the fig-ure shows. A perfect measurement would lieon a line with a slope of one. This is verymuch the case. The data are interestingbecause they show that the enrichment

calibration has little to do with the result.The squares in this figure are the resultusing a low-enriched uranium source (NISTstandard) for calibration. The triangles usedeclared values of highly enriched samplesfor calibration. Both results are good andtell us that the selection of calibrationsources does not affect the result.

S. John Luke and David A. KnappLawrence Livermore National Laboratory

Determining Uranium Enrichment

0

40

60

80

100

20

0 20 40 60 80 100Declared Enrichment

Mea

sure

d E

nri

chm

ent


Chain-of-Custody

To meet potential needs of the nextstage of U.S.–Russian nuclear armsreductions, Los Alamos National

Laboratory has developed two prototypesystems for monitoring the dismantlementand storage of nuclear weapons. TheIntegrated Facility Monitoring System(IFMS) was tested at the Device AssemblyFacility (DAF), Nevada Test Site in early1999. The Magazine Transparency System(MTS) added the ability to monitor nuclearweapons and components in storage priorto and after dismantlement. Both proto-types were demonstrated at the PantexPlant in October and November 1999.

These monitoring systems rely heavily onthe chain-of-custody concept. Chain-of-cus-tody offers inspectors confidence in the datathat confirm the status and location of alltreaty-limited items (in this case, nuclearwarheads and components). Inspectors arealso confident that no unauthorized tam-pering with the items has occurred.

Integrated Facility Monitoring System (IFMS)

Using a combination of sensors, tamper-indicating seals and tags, and a computer-based expert system, IFMS monitors thenuclear warhead dismantlement processpoint to point. It is designed to protectsensitive and classified information while

minimizing the impact of treaty monitoringon stockpile stewardship. For example, duringnormal operations, inspectors can remotelymonitor IFMS data at a central station locatedoutside the dismantlement facility.

All monitoring data collected by the IFMSare displayed in real time at the central sta-tion, and past events can be retrieved fromthe archives. Expert system software inte-grates sensor information with known disas-sembly protocols to ensure treaty complianceand maintain the inventory of treaty-limiteditems. Examples of protocol violations thatthe expert system can detect include excesstime of movement between process stages,inventory discrepancies, and the verificationof tamper-indicating seals and tags.

A key subcomponent of the IFMS, calledthe Integrated Tamper-Indicating Device(ITID), provides the uninterrupted surveillanceof sealed containers as opposed to periodicchecks of seal integrity. The ITID, mounted ona weapon or component container, consists ofa seal, camera, infrared tag, and UHF transmit-ter. This subcomponent tracks the location ofitems between steps in the dismantlementprocess and ensures that no unauthorizedtampering occurs.

Other sub-components, called integratedmonitoring stations, are placed outsideentryways to disassembly bays and cells.These stations track treaty-limited items as

Chain-of-Custody Monitoring of Warhead Dismantlement

Device Assembly Facility at the Nevada Test Site. Integrated Tamper-Indicating Device (ITID).


Chain-of-Custody

they enter and exit disassembly bays andmonitor the removal and re-attachment ofITIDs on weapon and component contain-ers. These subcomponents relay their datato the central station where the data can beauthenticated by inspectors.

Magazine Transparency System (MTS)The MTS detects unauthorized movement

of weapon containers from storage maga-zines and maintains their inventory. Thesystem uses only passive tags and seals toreduce host-country safety and security con-cerns. It maintains and transfers data on theinventory of stored treaty-limited items tothe IFMS central station. The systemdemonstrated at Pantex included the fol-lowing elements:• Gaussmeter• Low-light video camera• Radio-frequency identification (RFID) tag• MAGTAG blanket• Barcode reader• One-time keypad.

The gaussmeter measures the magneticfield within the magazine and detectschanges in that field caused by themovement of magnets in the MAGTAGblankets covering the containers. Thevideo camera detects any scene changes,

and the RFID system interrogates the RFtag on the MAGTAG blanket for additionalmotion detection.

All modules in the MTS run on a singlecomputer. The barcode is read on the arms-control seal for containers when they enter orleave the magazine. Data from the barcodereader—time stamp, reader number, and bar-code number—are transmitted from the MTScomputer to the IFMS central computer.

A single software system monitors eachof the MTS sensors (gaussmeter, video, andRFID) for movements within the magazine.If no movement is detected, the softwaresends an “ALL OK.” signal to the IFMS cen-tral system. An alarm is triggered if one ormore of the sensors detects movement.

Monitoring systems with the capabilitiesof the IFMS and MTS can help meet theobjectives of the 1997 U.S.–Russian HelsinkiSummit statement. This statement commit-ted the U.S. and Russia to increase thetransparency of nuclear weapons stockpilesand warhead dismantlement. These proto-types are a first step in meeting these long-term objectives.

James E. DoyleLos Alamos National Laboratory

Integrated Monitoring Station.


Chain-of-Custody

Apersistent challenge in transparencyregimes is that of reconciling specialnuclear materials (SNM) entering a

closed facility (i.e., one to which inspectorsdo not have access) with the materials leav-ing the facility following the dismantlementof a weapon or the processing of the SNM,without revealing anything classified abouteither the materials themselves or theprocesses they undergo within the facility.The search for a means to ensure that thematerial observed going in is the samematerial coming out was succinctly summa-rized by a policymaker: “Why can’t youpaint the SNM pink?” This pithy question isat the heart of a transparency tool called fis-sion-product tagging.

The SNM-bearing item is irradiated at theentrance of the facility with a neutronsource that produces fission products in the

SNM. Following processing within the facili-ty, the resulting pieces of SNM are examinedwith a high-resolution, gamma-ray detectorto determine whether they bear inventoriesof fission products consistent with the irradi-ation as it was performed. Most of the activi-ty of the fission products—the “pink paint”of the analogy—decays away within a fewdays, so that the intrinsic radiation of theSNM is not permanently increased (animportant radiation-safety consideration foroperations at a real processing facility); how-ever, key activities persist for the several tensof hours necessary for most forms of SNMprocessing to be completed.

Proof-of-concept experiments centeredaround the ARIES process (see sidebar, nextpage) to convert a classified weapon compo-nent into an unclassified form. TheGODIVA fast-burst reactor was used toinduce fissions in a component passingthrough ARIES. Measurements following thepassage of the SNM through ARIES revealedthat the fission products were transportedeffectively through the ARIES process; thatis, the physics “worked.” However, the neu-tron source required to induce a detectablenumber of fissions proved to be rather large.This creates health-physics implications forthe facility where fission-product tagging isimplemented. The research program,accordingly, has not yet proceeded to thedevelopment of a prototype tagging tool,but the satisfactory transport of the fissionproducts in the ARIES-oriented experimentsgives reasonable confidence that a taggingtool could be built should a dismantlementor conversion regime require one.


Fission-Product Tagging

Chain-of-Custody


Nondestructive Assay (NDA) methods quantify the pluto-nium and uranium contents of sealed containers without open-ing them by measuring the naturally occurring radioactiveemissions from the items inside the containers. NDA instru-ments include a calorimeter (measuring the heat output fromthe radioactive decay of plutonium), a neutron multiplicitycounter (measuring the neutrons produced by the sponta-neous radioactive decay of plutonium or the induced fission ofuranium), and gamma-ray detectors (identifying unique signa-tures from the isotopes to determine their relative fractions).

NDA measurements can be integrated with robotics andautomated under the control of a central computer. Roboticcontrol improves consistency, increases throughput, lowersoperating costs, decreases radiation exposure to operating per-sonnel, and improves nuclear-material safeguards.

Materials and residues from over 50 years of weapons pro-duction, now in storage, are being repackaged in long-termstorage containers at DOE sites around the country. For ulti-mate disposition, plutonium will be either mixed with ura-nium to form mixed-oxide (MOX) fuel for nuclear reactors, orit will be immobilized in glass logs to prevent its escape intothe environment or its theft by terrorists.

Los Alamos National Laboratory is also demonstratingtechnologies to dismantle nuclear weapons, convert the plu-tonium to an unclassified shape, and place it in DOE-approved containers. Products and residues from the disman-tlement process are quantified through integrated androbotically operated NDA methods.

Nondestructive Assay of Special Nuclear Materials

Thomas E. SampsonLos Alamos National Laboratory


Alternative Signatures

Acceptable verification methods mustfurnish just enough information touniquely identify items of concern,

without providing unnecessary information.Additional features that may be required ofa verification method include high speed,portability, and simple operation.

Pacific Northwest National Laboratory isdeveloping an electromagnetic inductionmethod (EM induction coil) as a non-nuclear approach to verification methods.The EM induction coil shows promise forobtaining unique, non-intrusive signaturesof weapon components.

A low-frequency, voltage-driven coilinduces a magnetic field (of a magnitudesimilar to the earth’s magnetic field) insidethe container, causing eddy currents to flowthroughout conductive components. Thecomplex-valued coil impedance, measuredin seconds, varies in response to a multi-tude of independent parameters describing

the container and the contents inside.Parameters that significantly influence theelectromagnetic signature include electricalconductivity, magnetic permeability, totalmass, mass distribution, and the orientationof each object interacting with the coil. Bythemselves, two-dimensional coil imped-ance measurements are insufficient toderive (invert) explicit information becausethe dimensionality of the complete parame-ter set influencing the signature is moreextensive.

The EM induction coil method has beenevaluated at the Pantex Plant and PacificNorthwest. Test items in these evaluationsincluded weapon components, models, anda wide assortment of metal objects selectedto characterize and optimize the capabilityof this method. To date, our results showthat this method can—• Uniquely identify metal containers, and

their contents

Identifying Weapon Components in SealedContainers by Electromagnetic Induction

Bronze

Wide BB cylinder

Steel

Tall BB cylinder

Titanium

304 Stainless Steel

Copper

Al (solid)Brass

Al (hollow)

6.4

6.4

6.4

6.4

6.4-1.0 -0.5 0.0 0.5 1.0 1.5 2.52.0

6.4

6.4

Ver

tica

l Vo

ltag

e

Horizontal Voltage

RSLC LS

RC

j

Secondary Induction CircuitPrimary Coil Circuit

e(t)

Eddyscope output for different metal objects placed in a steel drum surrounded by a coil.



• Sort weapon components according totype

• Sort objects made from different metalshaving the same geometry

• Sort objects made from the same metalhaving a different geometry

• Distinguish between a metal and anoxide.A failure modes and effects analysis per-

formed at Pacific Northwest and approvedby Pantex shows minimal risk, even in aworst-case scenario. This results from thefact that even with the maximum possiblecurrent in the coil, the magnetic fields aresimilar to the earth’s intrinsic magnetic fieldin amplitude. The EM coil system was oper-ated in the laboratory for several hours onbattery power, demonstrating remote opera-tion where AC power is unavailable.

The EM coil method requires less than aminute to obtain the signature and analyzeit. Positioning the coil over the containerrequires more time than the one-buttonmeasurement. The sealed container remainsuntouched during coil placement andremoval. These features make this methodappropriate for rapid evaluation of largestockpiles. The necessary electronics andapparatus are approved for export to allcountries. For warhead and fissile materialtransparency programs, this issue maybecome a limitation for more complex mea-surement methods.

Ronald HockeyPacific Northwest National Laboratory



Effective confirmation of nuclear-weapon dismantlement and subse-quent transportation and storage of

the nuclear components poses two seeming-ly incompatible requirements: detecting suf-ficient information about the enclosed com-ponents to ensure they contain the pre-sumed nuclear components, while preclud-ing access to sensitive information. Infraredcameras can monitor containers for thermal(heat) sources that continue to generateheat and at rates and over periods of timeinconsistent with anything other thannuclear materials.

A double-walled, heavily insulated stor-age container encloses a heat-generatingsource. The heat source results in a highertemperature inside the container than out-side. This temperature differential acrossthe walls drives the thermal energy out-ward. Heat flows at a rate dependent on

the resistance of the path to the heat flow,causing higher temperatures at the surfaceat locations of higher heat.

Three containers were imaged using acommercial infrared camera. A 20-watt heatsource was placed inside a single-wall AL-R8container and a double-wall AT400-R con-tainer. A second, empty AL-R8 containerwas placed nearby for reference. The ambi-ent temperature was about 20°C—a typicalroom temperature—and the temperature ofthe warmest areas of the containers was 2°Cto 4°C higher.

Some features are thermal reflections. Forexample, the two similarly shaped, coloredcircles on the faces of the two rear contain-ers are thermal reflections of the containerin front. However, the circle pattern on thelid of the front container clearly maps theinterface between the lid and its seat. The

Thermal Infrared Signatures of Containers

Infrared image of two containers with heat sources and one emptycontainer.

Representation of a heat source inside a sealed fissile-material storagecontainer showing typical heat flow patterns.



pattern of the red area on the rear right con-tainer is consistent with the location of thesource and the geometry of the container.

A low-cost alternative to infrared-camerathermography uses liquid-crystal appliquésthat convert the infrared to visible light,allowing visual monitoring and document-ing to be done with low-cost consumer-gradevideo or digital cameras. Experiments usedcommercial, self-adhesive liquid crystalsheets having temperature sensitivities rang-ing from 20°C to 40°C in four 5°C ranges. Tocover a wider range with sufficient sensitivityto detect the expected few-degree tempera-ture difference, the sheets were cut into half-

inch squares and arranged randomly in a 25x 25 “chip” array on the container lids (seefigure below).

Applications include any monitoring ofthe dismantlement operation and long-termstorage, verification of dismantled compo-nents being transferred, and confirmatorymeasurements. Infrared-based imagery’ssalient feature is that it exploits the non-nuclear, nonvisual, intrinsic heat-generatingcharacteristic of the items of interest, with-out compromising engineering data.

Charles R. BatishkoPacific Northwest National Laboratory

A low-cost alternative to infrared cameras is a random array of liquid-crystal “chips” on the lid of an AL-R8 storage container with anenclosed 20-watt source. Red represents the cooler portions of thelid while blue shows the warmer portions.


Tags and Seals

Tamper-indicating devices (TIDs) thatsupport security technologies andoperations will play a critical role in

transparency and nonproliferation. A TID isa tag or seal that detects tampering, orattempts at tampering, of a controlled item,such as a canister containing a weaponcomponent. A tag is a unique identifierbased on either applied or intrinsic features.A seal is a tag applied across an interface toindicate a breach. A TID also provides ameans for identifying and monitoring anitem to be secured, such as radiation detec-tion equipment stored at a point of entry.TIDs should have a unique signature thatcannot be counterfeited to identify the con-trolled item. The signature may contain ser-ial numbers, digital identification, a com-

plex reflective pattern, etc. that cannot beremoved without being detected. TIDs canbe expected to contribute to treaty-compli-ance transparency for controlling nuclear-weapon inventories under the Mayak FissileMaterial Storage Facility (FMSF)Transparency and the Trilateral Initiative.

The Tags and Seals Working Group(TSWG) was formed by the Joint DOE–DoDIntegrated Technology Steering Committeein 1998. TSWG was chartered to assess pastand current TID technology supporting ver-ification, compliance, and transparencyneeds and to make recommendations ofcandidate TID technologies for potentialmonitoring regimes such as Mayak FMSFTransparency and the Trilateral Initiative.TSWG surveyed existing TID technologies,both commercial and noncommercial, toprovide a baseline for future evaluations,recommendations, and demonstrations.Many of the commercial technologies areused in domestic safeguards. Some of thevery secure TID technologies were devel-oped under the START I program but neverimplemented. TSWG surveyed adhesiveseals, reflective particle tags, radio-frequencytags, loop TIDs, mechanical TIDs, andintrinsic TIDs.

TIDs serve a very important role in thetransparency regimes being developed. As acentral feature of any chain-of-custodyarchitecture for nuclear systems and compo-nents during transportation and storage,they create a documentation record that

Tags and Seals for a Potential StrategicArms Control Monitoring Regime

The first-generation Smart Boltand Reader, intended to sealAT-400R fissile-material storagecontainers, was developed bythe Russian Institute ofExperimental Physics, VNIIEF.


Tags and Seals

can be audited. TIDs can also monitor com-ponent or material inventories in intermedi-ate and final storage, and they can indicatetampering of data and equipment duringand between inspections. Finally, they arealso key components in containment andsurveillance systems composed of videocameras, recording stations, and access con-trols (such as motion detectors).

Technical specialists from the participat-ing parties must prove to their respectivepolicymakers that it is possible to maintaincontinuity of knowledge over nuclear mate-rials and the corresponding data and equip-ment used to verify and monitor them.Without technical measures to seal and tagnuclear items and materials, it is difficult toensure that the materials are as declaredwithout requiring an inordinate amount ofeffort verifying them. The importance ofsuccessfully evaluating and deploying effec-tive TIDs is great. Cooperative participationin selecting the devices to be used will helpreduce threats to the U.S., Russia, and inter-national security.

Selecting appropriate TIDs, establishingprocedures for their use, and actually imple-menting those procedures are important toany inspection system for warhead-disman-tlement transparency and weapons-materialbilateral or trilateral verification. By engag-ing in a fully cooperative effort, confidencein the devices and their assurances can bemaximized. Without a cooperative evalua-

tion-and-selection process, it is likely thatthe host will insist on using devices devel-oped within its own country.

Minimizing verification, thus reducinginspection effort, depends on using TIDsacceptable to all parties. Efforts to adoptcommon certification criteria, alreadyunderway within the international safe-guards community, would be useful inimproving the efficiency of the selectionprocess and the acceptability of the chosendevices.

Reaching an international consensus onacceptable TIDs and developing testing andcertification protocols are not easy. Thelevel of dependence placed on thesedevices, and the consequences of their fail-ure make evaluation and selection a criticalstep on the path to effective transparency ininternational disarmament activities.

Jennifer TannerPacific Northwest National Laboratory

Arden DouganLawrence Livermore National Laboratory


Tags and Seals

Tamper-indicating seals are designed todetect unauthorized access to a contain-er or door. Unlike locks, seals do not

necessarily bar an unauthorized entry—theysimply record that it took place. This type of“tamper detection” has long been consideredan important component of overall securityand safeguards for nuclear weapons and mate-rials. Seals will continue to play an importantrole in monitoring trilateral agreements, andU.S.–Russian joint nuclear safeguarding andprocessing programs.

Two serious problems with existing sealsfor transparency and treaty monitoring arevulnerabilities and conflicting goals.Regarding vulnerabilities, the unhappy factis that many types of seals potentially avail-able for nuclear applications can be defeat-ed, at least when they are used in a conven-tional manner. “Defeating” a seal meansgaining access to what it is protecting (bymanipulating the seal or replacing it with acounterfeit) such that the unauthorizedaccess goes undetected.

The second serious problem with existingseals is that virtually none were designedwith transparency and treaty monitoring inmind. Conventional tamper detection pro-vided by existing seals differs significantlyfrom what is needed for effective trans-parency and treaty monitoring in terms ofgoals, likely adversaries, environment, per-sonnel, economics, visibility, seal handling,and consequences of a security failure.

To address both problems, theVulnerability Assessment Team, in conjunc-tion with the new Applied Monitoring &

Transparency Laboratory at Los AlamosNational Laboratory, has undertaken the fol-lowing tasks:1. Optimize the security of existing seals by

developing improved (but still cost-effec-tive) protocols. This work has been con-ducted for DoD, DOE, IAEA, and privatecompanies.

2. Develop new seals that have better securi-ty and more of the attributes needed fortransparency and treaty monitoring. Sofar, this work has led to the developmentof four novel seal designs and four U.S.patent applications. These seals provideexcellent security and transparency at amodest cost. They are envisioned for useat Mayak and other venues.

3. Demonstrate new transparency and mon-itoring protocols that overcome many ofthe problems associated with seals andwith conventional security and safe-guards approaches. These protocolsemphasize certain attributes that webelieve are essential in any effective (andnegotiable) international transparencyand monitoring program:• Classified information is not released.• Monitoring hardware is provided by

the host, eliminating the use of foreignhardware and thus avoiding the safety,security, and espionage concerns thatinevitably arise.

Seals for Transparency and Treaty Monitoring


Tags and Seals

• The physical presence of foreigninspectors inside each side’s nuclearfacilities during dismantlement opera-tions is minimized, again reducing safe-ty, security, and espionage concerns.

• The use of conventional seals, encryp-tion, or information barriers is limited.Confidence in the integrity of host-supplied monitoring equipment is pro-vided via more trustworthy, low-techmethods. These include live, dynami-cally tested continuous sensor feeds;“choose or keep” protocols that let theinspectors randomly choose at the lastminute which of several monitoringmodules, components, or seals provid-

ed by the host facility are installed andwhich are kept by the inspectors foranalysis and reverse engineering tocheck for signs of tampering; and“keep the used parts” protocols thatpermit the inspectors to keep and ana-lyze monitoring hardware after it hasfulfilled its monitoring functions.

• Tags, seals, and use protocols are specifi-cally designed for treaty monitoring andtransparency that neither replace norcompromise those required for domesticnuclear security and safeguards.

Roger G. JohnstonLos Alamos National Laboratory

A few of the estimated 5,000commercial seals are shown. Nosignificance is attached to whichseals have been chosen for thisphotograph other than that anumber of them have beenused, are being used, or areunder consideration around theworld for various nuclear-relatedapplications.

All types of nuclear weapons use chem-ical explosives to rapidly assemble fissionable materials to criticality. The

presence of chemical explosives is anothernuclear-weapons attribute, as is the pres-ence of the special nuclear material itself.Unlike uranium and plutonium, explosivesdo not naturally emit radiation—they arecomposed of stable, non-radioactive chemi-cals. Because explosives cannot be identifiedby passive radiation counting, detectingexplosives is more challenging than identi-fying most radioactive materials.

The presence of explosives inside a closedcontainer can be detected by active radia-tion methods, for example, neutron interro-gation. For the past 10 years, IdahoNational Engineering & EnvironmentalLaboratory has developed and helped theU.S. military field a neutron-interrogationsystem called Portable Isotopic NeutronSpectroscopy (PINS). The PINS system

identifies range-recovered munitions thathave lost their identifying markings due to corrosion and exposure to the elements.PINS was designed to nondestructively iden-tify munitions and containers filled withchemical warfare agents, such as sarin nervegas. Chemical munitions are its most fre-quent application, but PINS can also identi-fy projectiles filled with smoke-generatingchemicals, such as white phosphorus, andmunitions filled with high explosives.

PINS, like most neutron-interrogation sys-tems, shines neutrons from a radioisotopicsource or a neutron generator into the objectbeing tested. Neutrons easily penetrate theobject’s housing, even the half-inch thicksteel wall of a 155-millimeter artillery shell.Inside the object, the neutrons excite theatomic nuclei of the fill chemicals, and thesenuclei in turn de-excite by emitting charac-teristic gamma rays. The gamma radiationescapes the item and is measured by a


Chemical-Explosive Detection by Neutron Interrogation

The Portable Isotopic NeutronSpectroscopy (PINS) setup in TA-18 at Los Alamos NationalLaboratory. The shapes simulatehigh explosives.

Detection of Nonnuclear Components

Graphite reflector

Polyethylenemoderator

Steel shippingcontainer

Liquid nitrogendewar

Explosive parts

Polyethylene moderator

Tungsten shadow shield

HPGe detector

252Cf source


spectrometer. The gamma-ray energy spec-trum identifies those chemical elementsinside the item and their relative abundance.

Neutron-interrogation measurements onsimulated high explosives were recentlycarried out at Los Alamos NationalLaboratory’s TA-18 (see page 24). An off-the-shelf PINS system used hollow hemispheri-cal shells made from simulated Composi-tion B high explosive. The mass of the sim-ulated explosive ranged from 1 to13 kilograms. Three gamma-ray peaks pro-duced by the 10.829-MeV nitrogen capturegamma are shown in the graph (red line).The blue line shows the low background inthis energy region when no simulatedexplosive is present.

A second series of measurements usedpolyethylene to enclose the simulated highexplosive. The polyethylene moderated andredirected the neutrons that passed throughthe simulated explosive without interaction.The polyethylene boosted the intensity ofthe nitrogen gamma rays by a factor of six.

Adding the polyethylene showed that PINScould identify the simulated explosive in aslittle as 500 seconds, or about 9 minutes.Because active methods for detecting explo-sives are well-understood, we see this neu-tron-interrogation method as a promisingtechnique for identifying nuclear weaponsthrough their high-explosive components.

A.J. Caffrey and B.D. HarlowIdaho National Engineering & Environmental Laboratory

Detection of Non-nuclear Components

A single gamma-ray energy at10.829 MeV indicates the pres-ence of nitrogen. Three peaksarise from this energy because ofenergy losses due to pair produc-tion in the high-purity germani-um spectrometer crystal. Themiddle energy peak, or “singleescape” peak is the most intense.The “double escape” peak is alsovisible. The three peaks are sepa-rated by exactly 0.511 MeV, therest mass energy of the electron.

20

15

10

5

0

Co

unts

11.010.810.610.410.210.09.89.6Gamma-ray energy (MeV)

Nitrogensingle escape

Nitrogen fullenergy peakNitrogen

double escape

SimulantBackground

David SpearsProgram ManagerDOE/NNSA, [email protected]

Al BoniSavannah River Technology [email protected]

Leigh BratcherPantex [email protected]

Gordon DudderPacific Northwest National [email protected]

M. William JohnsonLos Alamos National [email protected]

James JonesIdaho National Engineering & Environmental [email protected]

Jessica KehlOffice of the Secretary of DefenseCooperative Threat Reduction Policy [email protected]

Ed MastalDepartment of Energy, [email protected]

Dean MitchellSandia National [email protected]

Ken SaleLawrence Livermore National [email protected]

Michele SmithDepartment of [email protected]


Points of Contact

Points of Contact

ACNT lists the following names for the benefit of readers who may wish to contact programmaticrepresentatives directly.

NN-50’s Materials Protection, Control, and Accounting (MPC&A) program focuses on enhanc-ing the physical protection and material-accountancy infrastructure at former Soviet Union sitescontaining weapons-usable nuclear material. This work is augmented by the program’s involve-ment with enhancements to the regulatory framework within Russia, national-level materialaccounting, nuclear-material transportation, as well as other related activities. The program’s goalis to reduce the risk to U.S. national security of an undetected theft of weapons-usable materialfrom the former Soviet sites by enhancing their MPC&A capabilities. The placement of a yellowbox around a given type of facility on the diagram signifies that the program is involved, or isplanning to be involved, in infrastructure upgrades at these sites.

The Idaho Accelerator Center (IAC), located at Idaho State University, hasoperated since 1994 in partnership with the Idaho National Engineering andEnvironmental Laboratory and the Department of Energy

RESEARCHConducting fundamental and applied research in low-energy nuclearscience using accelerator-produced radiation

IAC provides university, government, and industrial scientists and engineersunparalleled research opportunities: Radiography, tomography, and nucleartechniques for nondestructive evaluation and nondestructive assay; industrialand agricultural applications of accelerator-produced radiation; ion and photon-beam analysis for environmental and mineral extraction needs; radiation sciencein medicine; radioisotope production; accelerator-based neutron therapy; radia-tion effects testing for semiconductor devices; instrument and radiation-detectortesting for weapons surety studies and fundamental nuclear physics research.

EDUCATIONOffering undergraduate and graduate degrees in physics, healthphysics, engineering, and applied science

IAC supports educational activities at all levels of Idaho State University’s aca-demic areas, including physics, health physics, engineering, waste management,geology, biological sciences, and health sciences. The University offers bachelor’sand master’s degrees in physics and health physics, and in cooperation with theCollege of Engineering, doctorates in engineering and applied science. Studentsparticipate in all IAC research and development. The research staff has publishedmore than 100 peer-reviewed publications over the past five years.

PARTNERSHIPS AND COLLABORATIONSTeaming with university government and commercial partners onapplied research, testing and technology deployment.

IAC offers technical expertise and state-of-the-art facilities for collaborationswith universities, government agencies, and commercial and industrial organi-zations. These partnerships promote practical advances in nuclear and radiationscience and facilitate the transfer of technology to the private sector. IAC collab-orations range from agricultural applications of accelerator-produced radiationto nondestructive examination through gamma-ray spectroscopy, radiography,and tomography. IAC partners conduct research and testing on applications inenvironmental remediation, waste management, chemical-weapons verifica-tion, contraband detection, and radiation effects.

Accelerator Applications andRadiation Science

Uranium

Uranium

Plutonium

Plutonium Plutonium

Uranium

Plutonium

Uranium

Reprocessing

Uraniummining

Uraniumprocessing

Highly EnrichedUranium

HEU weaponscomponent

Military use

Military use

Pre-1997

Post

-199

7, n

aval

fue

l, co

mm

erci

al

Pre-

1997

, wea

po

ns-

gra

de

Weapons stockpile

De-Matedwarheadstorage

Assembly

Civilian reactors

Plutonium productionreactors

Partsfabrication

Enrichment

High-levelwaste

storage

Pu wasteimmobilization

Navalreactor

rods

PuStrategic Reserve

Pu componentdisassembly and

conversionPu weaponscomponent

Cooperative Threat Reduction (CTR)

HEU Transparency

Material Protection, Control, and Accounting (MPC&A)

Mayak Transparency

Plutonium Production Reactor Agreement (PPRA)

U.S.–Russian Plutonium Disposition Agreement

Trilateral Initiative

Disassembly

Reprocessing

Mixed-oxidefuel production

HEU componentdisassembly and

conversion

Processing/downblending

Pu conversion and blending

HEUStrategic Reserve

Material

Storage

Warheadstorage/staging

Civilian reactors

Civilian reactors

StrategicReserve

Storage

StrategicReserve

Storage

excess

Storage

Uraniumfuel rods

Spentfuel

LEU

Naturaluranium

Spent

Naturalor LEU

Navalfuel

storage

Fuelfabrication

Fuelfabrication

Pu partsfabrication

Fuelfabrication

excess

Storage

Storage DispositionWeapons

DisassemblyWeaponsAssembly

MaterialsProduction

WeaponsStockpile

See reverse side for an explanation of this chart For an electronic copy of this file, contact the ACNT Production Office at Lawrence Livermore National Laboratory.

FACILITIES and INSTRUMENTATION• 21,000 sq. feet of laboratory space

• 0.5–25 MeV electron LinacShort-pulse mode: pulse widths: 30–50 ps, 10 nC/pulse, 0.5% beam energy spread-Long-pulse mode: pulse width: 4 µs, 2,000 nC/pulse-Repetition rate: single shot to 240 Hz-Three beam ports

• Two 4-MeV Linacs-Field radiography/neutron source capability

• Varitron Accelerator (Varian Associates Inc.)-2–12-MeV energy range-Pulsewidths: 500 ns to 4 µs Beam energy and current analysis-Capable of up to3000 R/min (@ 1 m)

• 18-MeV Linac (Varian Associates, Inc.)– Beam energy and current analysis– Pulse widths: 15 ns to 2 µs

• Two positive ion Van de Graaffs-High-Voltage Engineering, Inc.-2-MV potential

• Tandetron-High-Voltage Engineering, Inc. 1.5 MeV/amu

• D/T Neutron Generator-Sodern Genie 16

• Supporting Instrumentation-Calibrated 20-GHz sampling scope-Multi-parameterdata acquisition system-Calibrated PIN diodes-Internet 11 connection

• Fixed facility and field digital radiography and computed tomography systemsusing x-ray generators from 30–450 kV

SERVICES• Wide range of accelerator types available to researchers

• Customized user support

• Photon, electron, and neutron transport calculations for system applications

• Photon and neutron dosimetry

• Customized radiation detection system development

• Experimental verification of predictions and objectives

• Customized accelerator performance and modifications

• Single point-of-contact: simplified coordination between researchersexperimental needs and applicable resources.

CONTACTS

Dr. Frank HarmonDirectorIdaho State UniversityCampus Box 8263Pocatello, Idaho 83209Phone: 208.282.5877Fax: 208.282.5878Email: [email protected]

Dr. James L. JonesAssociate DirectorIdaho National Engineering andEnvironmental Laboratory (INEEL)PO Box 1625Idaho Falls, Idaho 83415-2802Phone: 208.526.1730Fax: 208.526.5208Email: [email protected]

Dr. Jay KunzeAssociate DirectorIdaho State UniversityCampus Box 8060Pocatello, Idaho 83209Phone: 208.282.2902Fax: 208.282.4538Email: [email protected]

Idaho Accelerator Center1500 Alvin Ricken DrivePocatello, Idaho 83209

www.iac.isu.edu

NNSA/NN/ACNT-SP01

National Nuclear Security Administration

Documents

R&D for Arms ControlFrancis Poda, Savannah River Technology Center George L. Cajigal, Threat Reduction Support Center Production Ofﬁce Arms Control and Nonproliferation Technologies