NPN 13(4) Inside - NuPECCswitchyard toward the accelerator. editorial Vol. 13, No. 4, 2003, Nuclear Physics News 3 Precarious Careers, Uncertain Futures I graduated with a degree in

Nuclear

Physics

NewsVolume 13/No. 4

Nuclear Physics News is published on behalf of theNuclear Physics European Collaboration Commit-tee (NuPECC), an Expert Committee of the Euro-pean Science Foundation, with colleagues fromEurope, America, and Asia.

Editor: Gabriele-Elisabeth Körner

Editorial Board

R. F. Casten, Yale R. Johnson, SurreyJ. D’Auria, Vancouver W. Kutschera, ViennaT. W. Donnelly, MIT Cambridge R. Lovas, DebrecenJ. Durell, Manchester M. Lozano, SevillaM. Huyse, Leuven (Chairman) I. Tanihata, RIKEN Tokyo

Editorial Office: Physikdepartment, E12, Technische Universitat München,85748 Garching, Germany, Tel: +49 89 2891 2293, Fax: +49 89 2891 2298,

E-mail: [email protected]

Correspondents

Argentina: O. Civitaresse, La Plata; Australia: A. W. Thomas, Adelaide; Austria: H. Oberhummer, Vienna; Belgium:

C. Angulo, Louvain-la-Neuve; Brasil: M. Hussein, Sao Paulo; Bulgaria: D. Balabanski, Sofia; Canada: J.-M. Poutissou,TRIUMF; K. Sharma, Manitoba; C. Svensson, Guelph; China: W. Zhan, Lanzhou; Croatia: R. Caplar, Zagreb; Czech

Republic: J. Kvasil, Prague; Slovak Republic: P. Povinec, Bratislave; Denmark: K. Riisager, Århus; Finland: M. Leino,Jyväskylä; France: G. De France, GANIL Caen; B. Blank, Bordeaux; M. Guidal, IPN Orsay; Germany: K. D. Gross, GSIDarmstadt; K. Kilian, Jülich; K. Lieb, Göttingen; Greece: E. Mavromatis, Athens; Hungary: B. M. Nyako, Debrecen;India: D. K. Avasthi, New Delhi; Israel: N. Auerbach, Tel Aviv; Italy: E. Vercellin, Torino; M. Ripani, Genova; L. Corradi,Legnaro; D. Vinciguerra, Catania; Japan: J. Imazato, IEK; H. Toki, Osaka; Malta: G. Buttigieg, Kalkara; Mexico: J.Hirsch, Mexico DF; Netherlands: H. Wilschut, KVI Groningen; G. van der Steenhoven, NIKHEF Amsterdam; Norway: J.Vaagen, Bergen; Poland: T. Czosnyka, Warsaw; Portugal: M. Fernanda Silva, Sacavén; Romania: A. Raduta, Bucharest;Russia: Yu. Novikov, St. Petersburg; Spain: B. Rubio, Valencia; Sweden: P.-E. Tegner, Stockholm; Switzerland: C.Petitjean, PSI Villigen; United Kingdom: B. F. Fulton, Birmingham; D. Branford, Edinburgh; USA: R. Janssens, Argonne;Ch. E. Reece, Jefferson Lab; B. Jacak, Stony Brook; B. Sherrill, Michigan State Univ.; L. S. Schroeder, Lawrence BerkeleyLaboratory; S. E. Vigdor, Indiana Univ.; W. C. Haxton, Seattle.

Nuclear Physics News ISSN 1050-6896

Advertising Manager

Maureen M. Williams, P.O. Box 1547Surprise, AZ 85378-1547, USATel: +1 623 544 1698Fax: +1 623 544 1699E-mail: [email protected]

Circulation and Subscriptions

Taylor & Francis Inc.325 Chestnut Street8th FloorPhiladelphia PA 19106, USATel: +1 215 625 8900Fax: +1 215 625 8914

Vol. 13, No. 4, 2003, Nuclear Physics News 1

Subscriptions

Nuclear Physics News is supplied free of charge tonuclear physicists from contributing countries uponrequest. In addition, the following subscriptions areavailable:

Volume 13(2003), 4 issues, Personal: 42 EUR,$52 USD, £32 GBP, $80 AUD, ¥9,000 JPY;Institution: 305 EUR, $421 USD, £229 GBP,$580 AUD, ¥64,000 JPY.

Copyright © 2003 Taylor & Francis Inc. Reproduction without permission is prohibited.All rights reserved. The opinions expressed in NPN are not necessarily those of the editors or publishers.

Nuclear

Physics

News

Volume 13/No. 4

Contents

Editorial .............................................................................................................................................................. 3

Laboratory Portrait

The Cyclotron Institute at Texas A&M Universityby Robert Tribble ............................................................................................................................................ 5

Feature Article

Using a Square Well to Introduce Nuclear Physicsby Sophie Heinrich and Jean-Luc Sida ........................................................................................................ 11

Facilities and Methods

AGATA: The Advanced Gamma Tracking Arrayby J. Simpson and R. Krücken ...................................................................................................................... 15

Francium Developments at Stony Brookby S. Aubin, E. Gomez, K. Gulyuz, L. A. Orozco, J. Sell, and G. D. Sprouse ............................................... 19

Impact and Applications

Selected Isotope Applications in Cosmochemistry and Geochemistryby Chris J. Ballentine and Ian Lyon ............................................................................................................. 22

Meeting Reports

Symmetries in Nuclei, Erice, March 23–30, 2003by Andrea Vitturi ........................................................................................................................................... 28

International Symposium on Physics of Unstable Nucleiby Dao Tien Khoa, Vo Van Thuan, Nguyen Dinh Dang, Shigeru Kubono, and Nguyen Van Giai ............... 29

Obituary ........................................................................................................................................................... 30

News from EPS/NPB ....................................................................................................................................... 31

Calendar ........................................................................................................................................................... 32

2 Nuclear Physics News, Vol. 13, No. 4, 2003

Cover illustration: A view of the K500 superconducting cyclotron at Texas A&M University, looking from the beam lineswitchyard toward the accelerator.

editorial


Precarious Careers, Uncertain Futures

I graduated with a degree in physicsin a southern country where thepossibilities of obtaining a permanentjob as a researcher are rather insignifi-cant. Like many of those who have lefttheir country of origin to work in aforeign laboratory, I started out yearsago on an unintentional path of noreturn. Taking advantage of Spanishnational grants and of the Europeanprograms of mobility, I have worked infive different nuclear physics andastrophysics groups in three differentcountries (Germany, France, andBelgium). Since 1998, I have been atthe cyclotron laboratory at Louvain-la-Neuve, but I do not have a permanentposition. This itinerant life hasdemanded from me a certain degree offlexibility, adjusting myself to the workprogram, conditions, and facilitiesoffered, and learning new skills, fromvacuum techniques to theoreticalmodels. Taking as mine the glory or themisery of the groups of which I havebeen a member over the years, I havehad the chance to discover a lot abouthuman nature. It has been an extremelyrich adventure. The drawback issometimes, but fortunately not always,weak support from the local groupswhen applying for a position. In anatural way, those who have graduatedfrom and received their Ph.D. degreein the group are preferred. This is acommonly accepted practice in all theuniversities where I have been and oneof the disadvantages of mobility. It maybe unnecessary to mention that the linkwith the home institute, if it existed atall, is broken when one works abroadfor many years.

Being a foreigner has not normallybeen an obstacle for me, but I havefound that being fluent in the languageof the country is a must if one wants tobe accepted and to play a role in theresearch activities of the group.Moreover, I have not been treateddifferently than my male colleagues.Being a woman has been neither adifficulty nor a benefit for my researchcareer. At least, this is what I haveperceived. I think it has been irrelevant,as it should be. But I realize that this isnot always the case. In general, it willbe a significant improvement whenbeing a woman will not be adisadvantage (but also not anadvantage) in getting a job. A stepforward will be achieved when genderwill be considered a marginal featureand positive discrimination will not beneeded anymore. On the other hand, thereality of so few women in keypositions in nuclear physics is aproblem common to other researchfields and it deserves a real debatewithin the scientific community. Itreflects a typical impasse within oursociety, which is amplified when onetakes into account the need for apermanent position near the placewhere the life partner works and thechildren go to school.

Coming back to my ownexperience, even though myemployment situation is fairly unstable,I feel fortunate. After 15 years innuclear physics, I am still doing what Ilike, in a state-of-the-art laboratory witha friendly environment, in a pleasantcountry, and with productive andenjoyable collaborations. When

planning future work, I have learned topay little attention to ill augurs and, inspite of the everyday uncertainty aboutfinancial support, I still enjoy nuclearphysics. However, it is not easy to carryout research under these conditions.Sometimes I believe that I havecompletely misjudged my choice ofcareer and I would not suggest thatothers follow my example. Many of thepeople from my generation, andespecially those coming after, do notknow other possible ways of doingresearch than this one: surviving fromone grant to the next, carrying on fromone contract to another. Our future innuclear physics is uncertain.

We all know brilliant youngresearchers who have been forced, notwithout bitterness, to leave nuclearphysics for a more secure job in theprivate sector or who have totallychanged their research area in order toget a position. These lost researcherscould have been the building blocks ofnuclear physics in future years. Hearingor writing myself about the bright futureof nuclear structure in Europe seemsunreal to me sometimes. The reality inEurope is that the number of permanentpositions in nuclear physics isdecreasing every year. As hard as it isto believe, it may well happen that acommission that examines theapplications for permanent positions inphysics does not include a nuclearphysicist among its members. This iscertainly anomalous and alarming.Although other fields in physics and,in general, in science may well sufferfrom the same illness, nuclear physicshas specific problems today. In spite of

The views expressed here do not represent the views and policies of NuPECC except where explicitly identified.


all the funding employed to build upand to develop nuclear physics researchfacilities in Europe (sometimesgargantuan enterprises withcorrespondingly gargantuan budgets),little attention is given to keeping astable and sufficient number ofpermanent professionals to drive theprojected research. Needless to say, weneed the experimental facilities. Butmore than ever, we need dedicatedresearchers who do not have to struggleto keep their jobs. Because, like it ornot, we are short of talented minds.

Are there people out there withhidden motivations for preventingnuclear physics from being wellrepresented? Certainly internal quarrelswith other physics disciplines create

damage and are a significant waste ofenergy and time. But I believe that theloss of permanent positions is, amongother things, the result of many yearsof nuclear physicists resting on theirlaurels, of the many nuclear physics“microgroups” being isolated, servingparticular interests rather than acommon coordinated goal (in spite ofthe considerable efforts of NuPECCand of the more recent researchinitiatives), and a deficient, or evennonexistent, publicizing of the benefitsof nuclear physics to society. It is alsoa problem of lack of lobbying at theEuropean, national, and regional levels.

How does one build a solidscientific program for the futurewithout firm foundations? I do not think

editorial

it can be done. I do not have thesolution, but we, the entire community,may still do something. Do not ignorethe problem. Do not accept it as acalamity. Do not stay passive in yourcorner. Take advantage of your positionand use your imagination to react now.Otherwise, when our senior colleaguesretire and the current Ph.D. students (ifany are left) are gone, no one will bethere to work on fundamental nuclearphysics research. On that day there willbe no one to blame except those whohad the responsibility to act but did not.

CARMEN ANGULO

Cyclotron Reseach CenterLouvain-la-Neuve


laboratory portrait

The Cyclotron Institute at Texas A&M University

Overview

The Texas A&M UniversityCyclotron Institute is jointly supportedby the U.S. Department of Energy andthe State of Texas. The centerpiece ofthe Institute is a K500 superconductingcyclotron, from which first beams wereextracted in 1988. Today, with twoelectron-cyclotron-resonance (ECR)ion sources, the accelerator can producea wide variety of beams: those withintensities of at least 1 enA range inenergy up to 70 MeV/A for light ionsand to 12 MeV/A for heavy ions suchas U. For the past decade the cyclotronhas averaged more than 6500 hours ofoperation per year.

The Cyclotron Institute wasinitiated by Texas A&M University justover 40 years ago. In the early 1960s aproposal was funded jointly by theAtomic Energy Commission, the R.A.Welch Foundation (a private foundationheadquartered in Houston, TX), and theState of Texas to construct an 88"cyclotron. Construction of theaccelerator was completed by 1967 andfirst beams were obtained from it in1968. The 88" cyclotron operatedcontinuously until 1986, when it wasdecommissioned, just prior to whenfirst beams were obtained from the newsuperconducting cyclotron.

In 1980, Texas A&M University andthe Welch Foundation jointly fundedthe construction of the K500 super-conducting cyclotron. The accelerator,was built by Institute staff in a buildingaddition that provided room for thecyclotron vault and new experimentalareas. Since completing the cyclotron,Institute staff have designed, con-structed, and upgraded the ECR sourcesused for injection into the acceleratoras well as ancillary equipment used

downstream from it. Figure 1 shows aschematic layout of the cyclotron andexperimental areas. The complement ofsophisticated state-of-the-art detectorsand spectrometers provides theinstrumentation necessary for researchin the areas of nuclear structure,fundamental interactions, exotic nuclei,nuclear astrophysics, intermediate-energy reaction dynamics, nuclearthermo-dynamics, the nuclear equationof state, atomic physics, and appliednuclear science. Approximately 100Institute members—scientists, engi-neers, technicians, support staff, grad-uate students, and undergraduates—areinvolved in these programs.

Research at the Cyclotron Institutecovers a broad range of topics inmodern nuclear physics at low andintermediate energies. Over the pastfew years, radioactive beams havebecome more of a focus for thelaboratory. High-purity secondary

beams are produced in the recoilspectrometer MARS via inverse-kinematics reactions that attain highefficiency. Recently the BigSolspectrometer has been commissionedand now serves as a second location thatprovides radioactive beams. Instituteprograms that rely on these beamsinclude studies of fundamentalinteractions, nuclear astrophysics, andheavy-ion reaction dynamics.

In addition to a broad researchprogram in nuclear science based on theK500 cyclotron, Institute researchersare involved in collaborations at severalother laboratories in North Americaincluding Brookhaven NationalLaboratory, Argonne NationalLaboratory, and TRIUMF. Below weprovide some details about the ongoingprojects.

Fundamental Interactions

In recent years, the Institute has

Figure 1. Schematic layout of the experimental facilities at the TAMU CyclotronInstitute.

developed an on-line facility speciallydesigned for precision measurements ofshort-lived nuclides. Currently it isfocusing on the study of superallowed0+ → 0+ nuclear β decay, which is ahighly sensitive probe of the vector partof the weak interaction. Measurementsof the lifetime, branching ratio, anddecay energy for such transitions yielda direct determination of the weakvector coupling constant, G

V, provided

that small radiative corrections areproperly accounted for. From G

V, it is

possible to establish a very precisevalue for V

ud, the up-down element of

the Cabibbo–Kobayashi–Maskawa(CKM) quark-mixing matrix of theminimal electroweak standard model.Not only does nuclear β decay yield themost precise determination of V

ud, but

that result is the most precise of anyelement in the CKM matrix. It alsoleads to the most demanding availabletest of CKM unitarity, a fundamentaltenet of the standard model. Strikingly,the test fails by more than two standarddeviations, a provocative outcome thathas motivated the quest for even greaterprecision in the determination of V

ud

(and of Vus

, the other key element in thetest).

The precision-measurement facilityis mounted at the end of MARS. Anisotope of interest, produced fromheavy-ion bombardment of a cooledhydrogen gas target, appears as a beamat the focal plane of MARS. It isextracted into air, degraded inaluminum, and then stopped in a thinmylar tape. The combination ofelectromagnetic separation in MARSand range separation in the degraderresults in sample impurity levels below0.1%. A fast tape transport systemmoves collected samples repetitively toa shielded counting location where theactivity can be counted. Typicalprecision on half-life results is 0.04%,

while branching ratios can bedetermined to 0.15%. Results fromstudies of 22Mg and 34Ar decay with thisfacility have already appeared [1, 2].How these results impact on thestructure-dependent radiative correc-tions is shown in Figure 2.

Isoscalar Giant Resonances and

Nuclear Compressibility

The first conclusive measurementsof the isoscalar giant monopoleresonance (GMR) in nuclei were madeby Institute researchers in the late

1970s. Since then, we have focused onobtaining more detailed informationabout them. The experimental programis based on the MDM magneticspectrometer and focal plane detectors,which allow us to use small-angle(including 0o) inelastic scattering withboth light-ion and heavy-ion beams atabout 60 MeV/A. Figure 3 shows theexcellent peak to continuum ratio forthe data as well as giant monopole andisoscalar dipole distributions derivedfrom the data. The isoscalar GMR andisoscalar giant dipole resonances


laboratory portrait

Figure 2. Experimental uncorrected ft-values (circles with error bars) comparedwith results of calculations (grey bands) that used recently calculated [3] structure-dependent radiative corrections. The calculated bands were obtained by applyingthe correction terms in reverse to the average corrected ft-value, which wasassumed to be universal. This then constitutes a sensitive test of the relativevariations in the correction terms. The 22Mg and 34Ar results, which must becompared to the dark grey band, are the only measurements to have been obtainedafter the calculations were produced and constitute important confirmation; theuncertainties of both can be improved by further measurements in progress.

(ISGDR) are of particular interestbecause their energies are directlyrelated to the compressibility of thenucleus (K

A) and, ultimately, to the

compressibility of nuclear matter(K

NM). K

NM is an important quantity for

both nuclear physics and astrophysics,as it is one of the key ingredients neededto understand neutron stars. UsingHartree–Fock random-phase-approx-imation calculations, the theoreticalprogram at the Institute explores therelationship between K

A and K

NM as

well as the comparison between modelpredictions and experimental strengthfunctions.

From the inelastic-scatteringmeasurements, we have obtained GMRand ISGDR strength distributions up tovery high excitation energy (E

x~ 30–

40 MeV) in many nuclei [4]. Both themass and isotopic dependence of GMRand ISGDR strength functions are beingstudied under circumstances in which100% (or nearly 100%) of the GMRstrength has been located in 18 nucleifrom 24Mg to 208Pb, which include fourisotopic series. Calculations that useK

NM ~ 230 MeV generally give GMR

energies consistent with the data.

N/Z Dependence of Nuclear

Interactions

The neutron-to-proton ratio (N/Z) ofreaction partners affects both thedynamics and the thermodynamics ofheavy-ion collisions. Predictions havesuggested that: (1) the difference in thechemical potential between neutronsand protons will change thethermodynamics governing the decayof excited nuclear matter when the N/Z ratio is changed; (2) a neutron-richsystem will undergo a type ofdistillation resulting in a low density or“gas” phase, which carries much of theneutron enrichment, and a high densityor “liquid” phase that is more


laboratory portrait

Figure 3. Recent results from inelastic scattering of α’s on 116Sn with the MDMspectrometer set at 0o. The spectrum shows excellent peak to continuum ratios.The GMR and ISGDR distributions obtained from the data are also shown.

symmetric; and (3) the dynamics ofreactions leading to excited nuclearsystems will depend on N/Z.

Institute researchers are studyingthese N/Z dependencies in heavy-ionreactions by comparing what happensduring collisions of different isotopes,such as 20F, 20Ne, and 20Na. Measure-ments with light and medium-massheavy-ion beams are being carried outwith the FAUST detector systemlocated at the back of either MARS orBigSol [5]. The measurements areshedding light on how N/Z affects thedeep-inelastic transfer process and areproviding new information on ways toproduce neutron-rich heavy residues.

Properties of Hot Nuclei

Experiments are being carried outto determine the thermodynamicproperties of very excited “hot” nucleiproduced in intermediate-energyheavy-ion collisions in order to explore(1) the nuclear equation of state undernonnormal conditions; (2) the nature ofthe “liquid–gas” phase changes instrongly interacting, finite quantumsystems; and (3) the relationship of suchchanges to those in bulk nuclear matter.Our focus is on developing ways toextract direct information on the extentto which equilibration of variousdegrees of freedom is realized and tounderstand the dynamical andthermodynamical evolution of theinteraction region. If a collisionproduces sufficient thermal and/orcompressional shock, the hot compositenucleus that results may expand to lowdensity, then cluster and disassemble.If this multifragment disassembly isthat of a thermally and chemicallyequilibrated nucleus, information oncritical behavior and the liquid–gasphase change in nuclear matter shouldbe accessible [6].

To pursue this research, Institute

staff constructed the NIMRODdetector, a 4[ charged-particle arraylocated inside a 4[ neutron calorimeter.The NIMROD array, in addition toproviding high geometric coverage, haslow detection thresholds and a largedynamic range for light charged-particle detection and allows isotopicidentification to at least Z=10, as shownin Figure 4.

Nuclear Astrophysics

Over the last decade we have seenan explosion of new information inastrophysics, ranging from a glimpseat the earliest events in our universe to

a more detailed view of the continualevolution in stellar systems thatsurround us. Cosmology theories tell usthat, within an instant after the BigBang, nuclear synthesis was driving theevolution of the universe. To under-stand this evolution we requireinformation about a wide range ofnuclear reactions, many of whichinvolve an unstable nucleus capturinga proton or an alpha particle andtransmuting to a new unstable nucleus.Until the recent advent of radioactive-ion beams, it was nearly impossible tostudy such reactions in the laboratory.Now, Institute researchers are using

laboratory portrait


Figure 4. An example of isotopic separation with the charged particle array inNIMROD. Combining this with information on the neutron yields provides apowerful way to characterize the nuclear matter produced in heavy-ion collisions.

laboratory portrait


radioactive beams produced in MARSto learn more about some of theimportant nuclear reactions governingthe behavior and evolution of our ownsun and other stars.

The approach that has beendeveloped involves a combination ofradioactive-beam-induced reactionswith conventional nuclear-physicstechniques. The strength of theasymptotic wave function—theasymptotic normalization coefficient,or ANC—is determined from aperipheral transfer reaction. Then theANC is used to determine the reactionrate for direct proton-capture reactionsat stellar energies. This technique hasbeen used to determine stellar-capturerates for reactions such as 7Be(p,γ)8B,the sole source of high-energy neutrinosfrom our sun [7]; 11C(p,γ)12N, animportant reaction to bypass the tripleα process in massive stars [8]; and13N(p,γ)14O, one of the reactions in thehot CNO cycle. Measurements withstable beams and targets have also beenperformed.

Ion Interactions

The ion-interactions program iscurrently addressing three topics: (1)electron capture and loss by fast, high-Z ions, (2) cross sections for K-vacancyproduction in heavy-ion-atom col-lisions, and (3) x-ray satellite structurearising from multiple ionization inheavy-ion-atom collisions. The firsttopic is motivated partly by afundamental interest in the collisiondynamics of ionization and charge-exchange processes in fast, heavy-ioncollisions and partly by the current needfor electron-loss cross sections in orderto evaluate the prospects of heavy-ioninertial fusion as a possible energysource. Also, a detailed knowledge ofelectron-capture and -loss crosssections is required for the accurate

calculation of projectile charge-statedistributions, a problem of particularimportance in accelerator design.

The accurate theoretical predictionof cross sections for K-vacancyproduction, our second topic, has beena longstanding goal in the field of ion-atom collisions. Institute researchershave been performing systematicmeasurements of K-vacancy pro-duction cross sections in a continuingeffort to explore their dependence onprojectile energy and atomic number,and upon target atomic number. Recentwork on this topic has disclosed largediscrepancies between theory andexperiment for projectiles with atomicnumbers greater than 10 [9]. For thethird topic Institute researchers areperforming high-resolution measure-ments of the L x-ray spectrum ofholmium to examine the satellitemultiplet structure and to deduce theassociated distributions of L-, M-, andN-shell vacancies.

Radiation Effects

Over the past decade, use of ourfacility to test the response of electroniccomponents to radiation has grownsteadily to the point that it now occupiesabout 20% of the available beam time.The major motivation for tests is tocertify components for space flights.Solar flares, cosmic rays, and theEarth’s Van Allen belts serve as naturalsources of space radiation. Suchionizing radiation can “upset” thenormal function of semiconductorcomponents found in orbitingcommunications satellites and spacevehicles. The rates at which semi-conductor devices “upset” can bemeasured in the laboratory with beamsof high-energy ions, such as thoseaccelerated by the K500 cyclotron. TheRadiation Effects Facility (REF) end

station consists of dosimetry andenergy-degrader systems with com-puter-controlled device staging at testlocations in both air and vacuum.

Nuclear Theory

Nuclear theorists at the Instituteattempt to explain phenomena that areobserved in nuclear interactions at awide range of energies, from thoseavailable at the K500 cyclotron to thoseat RHIC. In one area of study, thetheory group has proposed variousways to study the nuclear symmetryenergy in collisions with radioactivebeams, including measurements of boththe preequilibrium neutron/proton ratioand of two-nucleon correlationfunctions and the production of lightclusters. They have found that theseobservables are sensitive to the densitydependence of the nuclear symmetryenergy, an essential property requiredfor an understanding of the structure ofradioactive nuclei and of manyimportant issues in nuclear astro-physics. At higher energies, such asthose at GSI, the group has suggestedthat new information about the nuclearequation of state can be obtained fromsubthreshold kaon production. Thesetheoretical studies are based on arelativistic transport model, RVUU,developed at Texas A&M University[10]. This model has been extendedfurther to probe the physics of hot densematter produced in heavy-ion collisionsat the even-higher energies availablefrom the AGS at Brookhaven NationalLaboratory. For relativistic heavy-ioncollisions at RHIC, the group hasdeveloped a hybrid model that includesboth initial partonic and final hadronicinteractions. It has been used to extractsignals of the quark-gluon plasma,which is expected to be produced inthese collisions.

Research Outside the Laboratory

Cyclotron Institute scientists alsoparticipate in the BRAHMS and STARcollaborations at RHIC, the TWIST andsuperallowed-beta-decay collabor-ations at TRIUMF, and the CPT col-laboration at Argonne. The BRAHMSgroup focuses on the study of very highrapidity phenomena, especially in p–pcollisions. The STAR group focuses onstudies of high-transverse-momentumphenomena and the spin of the proton.Early results show that high-transverse-momentum particle production isstrongly suppressed in Au–Aucollisions at RHIC, indicating that themedium created is very dense anddissipative [11]. Future plans includemeasurements of the gluon polarizationin the proton. TWIST will determinethe Michel parameters that characterizethe space-time structure of muon decayto a few parts in 104. Any deviationfrom expectations of the standardmodel would require the introductionof right-handed weak currents or othernew physics. The beta-decay studiesat TRIUMF and the mass measure-

ments undertaken with the CPTcollaboration at Argonne complementour local superallowed beta-decayprogram by providing results that arenot accessible here.

Future Directions

Over the past few years, Institutestaff members have developed a plan toupgrade the present facility to one thatwould yield high-quality radioactivebeams directly from the K500 super-conducting cyclotron. The first stage ofthe plan involves recommissioning the88" (K150) cyclotron. Intense light-ionand heavy-ion beams from thatcyclotron will be used to produceradioactive ions, which will then beslowed down in a He-gas stopper andcollected by ion guides as 1+ ions. A 1+-to-n+ ECR ion source will then be usedto produce the highly charged radio-active beams for reacceleration in theK500 cyclotron. The project will costaround $4 million and take about threeyears after initial funding to complete.It is envisioned that many aspects of the

laboratory portrait


project will provide valuable input toRIA development. Details can be foundin a white paper on our website athttp://cyclotron.tamu.edu/.

References

1. J.C. Hardy et al., Phys. Rev. Lett. 91,0852501(2003).

2. V.E. Iacob et al., Bul. Am. Phys. Soc.48, 34 (2003).

3. I.S. Towner and J.C. Hardy, Phys. RevC 66, 035501 (2002).

4. D.H. Youngblood, Y.-W. Lui, and H.L.Clark, Phys. Rev. C 65, 034302 (2002);63, 067301 (2001); 60, 014304 (1999).

5. D.J. Rowland et al., Phys Rev C 67,064602 (2003).

6. R. Wada et al., Phys Rev C (submitted).7. A. Azhari et al., Phys Rev C 63, 055803

(2001).8. X. Tang et al., Phys Rev C 67, 015804

(2003).9. R.L. Watson et al., Phys. Rev. A 62,

052709 (2000).10. C.M. Ko, Prog. Nucl. Part. Phys. 42, 109

(1998).11. J. Adams et al., Phys. Rev. Lett. 91,

072304 (2003).ROBERT TRIBBLE

Texas A&M University


feature article

Using a Square Well to Introduce Nuclear Physics

SOPHIE HEINRICH

CEA DSM/DAPNIA/Service de Physique Nucléaire, Saclay, France

JEAN-LUC SIDA

CEA DAM/DPTA/Service de Physique Nucléaire, Bruyères-le-Châtel, France

In reviewing the promotion and teaching of nuclearscience (PANS), we present an approach that has workedwell with French students in a third year master’s class. Weuse a nuclear square well to explain the shell model. Thisapproach is attractive, as it stems largely from oneobservation: that nuclear radii vary as A1/3. Students are ableto make calculations unassisted and also address questionssuch as the evolution of energy levels with nuclear mass,the nonexistence of mass 5 and 8 stable nuclei, or the shellclosures and magic numbers.

Herein, we present a few worked examples and give avery simple program (see box) for finding the single-particleenergy levels in the nuclear square well.

We are certainly not the only ones doing that, and we donot claim that it is something new since this model has beenused for a long time; it is just a natural and very coherentway to introduce the nuclear shell structure realm.

Why the Nuclear Mean Field Could Be Approximated

by a Square Well

Our aim is to build a toy model, ruled by only a few

principles, that yet captures the essence of the nuclear world.The following fundamental assumption will serve as thebasis: stable nuclei may be treated as spheres with sharp edgesthat grow with A, the number of nucleons. To be consistent,we thus have to use a nuclear attractive force which is fastlysaturating; for reasons of straightforwardness, we choose azero-range interaction. A nucleon is then submitted to apotential proportional to the negative of the nuclear densityof its nucleus. The nuclear density, and therefore the meanpotential, can be approximated by a step function with aconstant height and a width R varying as A1/3 .

How to estimate the depth of the potential? Since, a priori,we don’t know the magnitude of that well, we use theevolution of the nuclear radius within the framework of theFermi gas model to solve the inverse problem. For A freeparticles closed in a sphere of radius R

0A1/3, the Fermi energy

associated is equal to 53 MeV/ R0

2. Assuming the standardvalue of R

0 = 1.2 fm and taking into account the mean binding

energy per nucleon assumed at 8 MeV/nucleon, this leads toa potential felt by a nucleon, independent of the mass of thenucleus, equal to 45 MeV [1].

Program to find the nuclear square well eigenstates with Mathematica®

This file will calculate and plot the working function W * (Figure 2), corresponding to an orbital momentum l=0 (noted ll at the end of theprogram) and a mass A=208 (noted aa). Changing ll and/or aa, one can calculate any level for any nuclei.

rzero = 1.2rmasse = 931hbar = 197.3vzero = 53 / rzero^(2) + 8Rayon[a_] = rzero*a^(1/3)z1[a_,e_] = Sqrt[2.*rmasse/hbar/hbar*e]*Rayon[a]z2[a_,e_] = Sqrt[2.*rmasse/hbar/hbar*(vzero-e)]*Rayon[a]h[l_,zz1_] = BesselK[l + 1/2, zz1]/Sqrt[zz1]j[l_,zz2_] = BesselJ[l + 1/2, zz2]/Sqrt[zz2]W[l_,a_,e_] =((l*j[l,z2[a,e]]-z2[a,e]*j[l+1,z2[a,e]])/(j[l,z2[a,e]])-(l*h[l,z1[a,e]]-z1[a,e]*h[l+1,z1[a,e]])/(h[l,z1[a,e]]))ll = 0aa = 208Plot[1/W[ll,aa,e],{e,0,vzero}]

* This W function is different from the previous one. It has been built to increase the contrast and to avoid spurious divergences.

The nuclear square well is now clearly defined (Figure1), and from that potential, we may obtain the single-particleenergy eigenstates for any given nucleus of mass A.

Solving the Equations

With such a potential, spherical symmetry is assured, sothe radial and angular variables r, θ, ϕ could be separated,and the wave function of the states is the product of a radialfunction and a spherical harmonic [2]. The radial function isthe Bessel function j

l inside the well and the Hankel function

hl outside [2]. Using recurrent relations between Bessel

functions, the continuity of the two functions and of theirderivatives at the surface of the well imposes the followingcondition: W ≡ z2 jl+1(z2)hl(z1)–z1hl+1(z1) jl(z2)=0 with

z1 =

and

z2 = ,

where a and V0 are the ridge and depth of the well, m is the

nucleon mass, and E is the energy of the eigenstate of orbitalmomentum l.

For a given orbital momentum l, the energy of the stateswill be given by the zeros of the W function. We use 1/W toshow graphically, from the computer, the solutions asdivergences. This allow us to build the single-particle levelsfor any nuclei. In Figure 2, we can see the different s-statesfor a square well corresponding to lead.

Wave Functions and Densities

As the spherical harmonics are tabulated [3], the total

feature article

wave functions could be calculated, like for the lead 2d level,which is displayed in Figure 3, where the particular projectionof the angular momentum m=0 is plotted in the plan (r, θ).We can also show that the principal quantum number, liken=1, 2 or 3 used in Figure 2, corresponds to the number ofnodes of the wave function of the states.

The nuclear density is now determinable by squaring thewave function. For instance, we have extracted the 206Pbdensity, shown in Figure 4, as decomposed into its orbitalangular momentum components. The contribution to the totaldensity of each occupied state is determined taking intoaccount the (2l+1) degeneracy of the l states, the spindegeneracy, and the constitution (N, Z) of the nucleus. Theprotons and neutrons are being considered into two separatedbut identical wells (the reduction of the proton well, comingfrom Coulomb interaction, can eventually be added).

The radial wave function outside the well is a functionlike h0(r) = exp(–√αEr)/√αEr , where E is the energy of thestate. For low binding energies (E ~ 0), the wave functionand so the density of probability will extend over a largeregion of space. Even with this simple model, we are able toillustrate some new effects that emerge for nuclei near thelimits of stability.

Level Evolution with Masses

We can obtain the energy levels for any nucleus, givingthe mass number A and a chosen orbital momentum l. Thelevels are not at fixed positions and we can follow the


Figure 1. The nuclear square well. The radius correspondsto the nuclear radius. The depth is the Fermi gas potentialenergy (E

F) for a nucleon gas closed in the volume of a

nucleus plus the mean binding energy B.Figure 2. Function 1/W as a function of the energy for anucleus of mass A=208 and an orbital momentum l=0. Thebound states correspond to divergences. Three bound levelsexist for such a nucleus, 1s (41.5 MeV), 2s (31.5 MeV), and3s (15 MeV).

feature article

evolution of levels with mass, as given in Figure 5. The lastbound level for light nuclei is close to the Fermi energy, sothere are no possible excited states below threshold, whereasfor heavy nuclei, the Fermi level is deep inside the well,which allows many possible bound excited states.

This level energy dependence with mass implies a naturaldependence on nuclear binding energies. The total bindingenergy of a nucleus may be thought naively to be the sum ofthe individual single particle energies. However, since as oneincreases the mass, a given l-state appears at a deeper energy,an overall constant binding energy per nucleon is notincoherent.

This is a fundamental difference between the square welland the infinite potential such as the harmonic oscillator:the latter is mass independent and all levels of fixed energyare bound.

Examples

Inexistence of Mass 5 and Mass 8 NucleiThe observation of the nonexistence of mass 5 and mass

8 stable nuclei is important not only to nuclear physics butalso to astrophysics. Astrophysicists have for a long timenoticed the premature abortion of nucleosynthesis a fewminutes after the big bang, being able to build up nuclearspecies only to mass 7. Indeed, the stop of big bangnucleosynthesis is mainly due to the lack of stable isotopesof mass 5 and 8.


This inexistence is explained naturally using our toymodel. Let’s calculate the energy levels for a mass 5 nuclei.The energy levels of this nucleus are calculated looking forl = 0 and l =1 solutions. One l = 0 state exists at -19 MeV, butthere happen to be no l = 1 bound states in such a model formass 5 nucleons. This is not specific to R

0 = 1.2 fm and V

0=

Figure 3. Wave function of 1d-state (l=2) of 208Pb, for theprojection of the orbital momentum m=0, as a function ofthe spherical coordinates r and θ with φ=0.

Figure 4. 206Pb density (upper curve) with the decompositionin the different orbital momentum contributions (from left toright, contribution of s-, p-, d-, f-, g-, and h-states).

Figure 5. Evolution with mass of the single particle levels fromA=1 (left) to A=208 (right). All levels are not present for a givenmass. As the mass increases, the levels go deeper and deeper inthe well. The function drawn here is Log[Σ|1/w(l,A)|].l

45 MeV but true for every reasonable value of R0 with its

associate V0.

The situation for mass 8 is slightly different. Thenecessary levels to build mass-8 nuclei do exist, since ourprogram indicates an l = 0 state existing at 24 MeV and an l= 1 state at 5 MeV. The total binding energy of such a nucleuswould be -116 MeV. However, the transumutation of 8Beinto two 4He tends to readily occur, given that the bindingenergy of the 4He nucleus (about –65 MeV in our calculation)would lead to a deeper potential for the two-4He system.Further, the energy available in this decay is sufficient toovercome the Coulomb barrier (acting as a confiningpotential in this case); the reaction lies some 12.5 MeV abovethe barrier. Hence, primordial 8Be nuclei were doomed toalways decay.

Shell Model for Heavy NucleiFor a heavy nuclei like lead, the order of the levels is

(1s)(1p)(1d)(2s)(1f)(2p)(1g)(2d)(1h)(3s)(2f)(1i)(3p). Thisorder of the states leads to shell closures 2-8-18-20-34-40-58-68-90-92-106-132-138. . . . These, however, are not theobserved magic numbers of nuclei. They correspond, in fact,to the magic numbers of metallic clusters: 8, 20, 40, 58, 92,138, . . . [4]. Like nucleons in nuclei, the atoms of metallicclusters are subject to a short-range force, so the square wellis also a good approximation for such a system.

One important ingredient is missing in the case of nuclei:it is the spin-orbit potential, first introduced by the Nobelprize winners Mayer and Jensen. By adding a spin-orbitpotential to the nuclear square well, they were able toreproduce the nuclear magic numbers. This could be repeatedby students fairly simply, given the form of the spin-orbitterm such as –L.S, which induces a splitting of the levelsand a new sequence where the numbers 2, 8, 20, 28, 50, 82,126 appear like shell closures. While such a simple versionmay not give the correct large energy gap, it is sufficient forthe purpose of this project.

Summary and Conclusion

As a pedagogical tool, this toy model presents manyadvantages compared to other ones. It could be usedinteractively within a classroom environment and easilymanaged by students with mathematical libraries. In addition,these ones particularly appreciate the realism of a finite well(which, unlike infinite potential models, explains naturallythe emergence of levels with the increase in mass) and thelogical reasoning used here: the primary observation of the

A 1/3 dependence of the nuclear radius leads directly to theshells in the nucleus, with the exception of the requiredaddition of a spin-orbit term. Furthermore, this model is asrich as it is simple; while we have shown only a fewexamples, others can be done, including the calculation ofsuper heavy elements by the addition of a Coulomb term toreduce the proton well or the estimation of the probability ofa proton decay in the radioactivity of 6He.

In the end, this model, used as a heuristic tool, appears tobe a precious help to students trying to learn the “nuclearway of reasoning” by themselves.

Acknowledgment

We warmly thank M. Cassé, A. Drouart, S. Karataglidis,and E. Tryggestad for their help in the preparation of thisarticle.

References

1. A. Bohr and B. Mottelson, Nuclear Structure, W.A. Benjamin(1969). (For the Fermi gaz, see p. 139. For the nuclear density,see p. 159.)

2. L. I. Schiff, Quantum Mechanic, McGraw-Hill, 2nd ed. (1955).(For the eigenstates in a square well potential, see p. 76.)

3. M. Abramowitz and I. A. Stegun, eds., Handbook ofMathematical Functions, Dover (1970).

4. S. Bjørnholm et al., PRL 65 (1990) 1627.

S. HEINRICH

J.-L. SIDA

feature article



facilities and methods

AGATA: The Advanced Gamma Tracking Array

For decades, the study of thegamma-ray decay of the quantal statesof the atomic nucleus has played apivotal role in discovering andelucidating the wide range ofphenomena manifested in its structure.Each major technical advance ingamma-ray detection devices hasresulted in significant new insights intothe structure of nuclei. To date, theseadvances have culminated in two state-of-the-art 4[ arrays of escape-suppressed spectrometers, Euroball inEurope and Gammasphere in the USA.

With the advent of the firstgeneration of radioactive beamfacilities, dedicated medium-sizedetector arrays (e.g., MINIBALL andEXOGAM in Europe) have beenconstructed with the specific aim ofstudying the electromagnetic radiation

from reactions of fast-moving, short-lived exotic nuclei, with beamintensities several orders of magnitudelower than what is typically used atstable beam facilities.

The global consensus of opinionnow is that the next major step in γ-rayspectroscopy involves abandoning theconcept of a physical suppression shieldand achieving the ultimate goal of a 4[Ge ball through the technique of γ-rayenergy tracking in electricallysegmented Ge crystals [1, 2]. Theresulting spectrometer will have anunparalleled level of detection powerto nuclear electromagnetic radiation. Itssensitivity for selecting the weakestsignals from exotic nuclear events willbe enhanced by a factor of up to 1000relative to its predecessors (Figure 1,left side). It will have an unprecedented

angular resolution making it ideallysuited for high-energy resolution evenat velocities of the emitting nuclei upto 50% of the velocity of light (Figure1, right). It is therefore superbly suitedto be used in conjunction with the newgeneration of radioactive beamaccelerators or existing stable beamfacilities.

High-precision γ-ray spectroscopyis one of the most powerful probes ofthe structure of excited nuclear statesand so the impact of a massive increasein the efficiency and sensitivity in thisarea will be far-reaching, both in thestudy of nuclear structure and in theclosely related disciplines of nuclearastrophysics and fundamentalinteractions.

The new challenges for nuclearspectroscopy which provide the

Figure 1. Left: Plot of the spectroscopic sensitivity as a function of spin for various arrays showing the evolution of gamma-ray detection technology. The large gain provided by a 4R tracking array, such as AGATA, is clearly shown. Right: Simulatedspectrum for ca. 2.5 MeV γ-rays emitted from a source that moves with 20% of the velocity of light. A resolution of 8keV isexpected for AGATA, which should be compared with 80 keV (the broad structure) for a current generation large array, e.g.,EUROBALL.

impetus for AGATA are emergingprincipally from the new generation ofhigh-intensity radioactive ion beamfacilities currently being developedworldwide. These provide beams withenergies spanning the Coulomb energyregime, typical of the European ISOLfacilities (SPIRAL, REX-ISOLDE), tothe intermediate and relativistic energyregimes of fragmentation facilities,such as SIS/FRS at GSI. AGATA is vitalfor these laboratories and for theplanned major new facilities at, e.g.,GSI and for EURISOL. In the Coulombenergy regime the classical reactiontypes (Coulomb excitation, transfer,deep-inelastic, or compound reactions)will become possible using increasinglymore exotic radioactive beams allowingessentially all facets of nuclear structureto be probed in hitherto inaccessibleregions of the nuclear chart. Atintermediate energies, between 50 and200 A MeV, Coulomb excitation can beemployed to pick out states connectedto the ground state by sufficientlystrong electromagnetic matrixelements, up to and including the highlyexcited giant resonances. At evenhigher beam energies the single particlestructure of ground state and excitedstates of the most exotic nuclei can beprobed by means of knock-out andCoulomb break-up reactions. At theseenergies secondary fragmentationbecomes a powerful tool to create veryexotic fragments that are excited torelatively high spins of more than 30h– .Finally, the rarest species, closest to thedrip lines, can be studied using decayspectroscopy after implantation. Thismassive increase in experimentalaccess to phenomena in unexploredregions of the nuclear chart, offered bythe new generation of exotic beamfacilities, can only be fully exploitedwith the matching leap in experimentalsensitivity offered by AGATA.

The combination of high-efficiency,high-resolution γ-spectroscopic studiesand exotic beams will allow a very richphysics program to be addressed thatcovers the full gamut of topics whichcurrently engage the nuclear physicsresearch community. The study ofstructure at the very limits of nuclearstability is crucial in order to answersome of the most pressing questions inthe field. These include the isospindependence of the effective nuclearinteraction, the ability to explaincollective phenomena from theproperties of the individual nucleons,and the limits of nuclear existence andindeed Mendeleev’s table of theelements. In the last decade, it hasbecome clear that many of ourpreconceptions of nuclear structurehave to be revised. Nuclear radii are notalways proportional to A1/3; instead,neutron-rich nuclei develop a diffuseregion of neutron “skin” or “halo”

which can extend much further. Thevalues of the magic numbers of thenuclear shell model for neutrons andprotons are no longer sacrosanct: thestrength of the T = 0 part of thenucleon–nucleon interaction means thatthe position of the neutron (proton)shell closure varies with the proton(neutron) number. The number ofneutron-rich nuclei which can exist isfar greater than anticipated:improvements in the treatment of theself-consistent nuclear problem,including more realistic estimates ofcorrelations and clustering, predict aneutron drip line which seems to beconstantly receding. AGATA will focuson all these aspects through studies of,for example, (i) proton-rich nuclei atand beyond the proton drip line and theextension of the N = Z line, (ii) neutron-rich nuclei towards the neutron drip linein medium heavy elements, and (iii) theheaviest elements towards new super-



Figure 2. A possible scattering path within one 36-fold segmented detector isindicated. Energies and scattering angle are related by the Compton scatteringformula. Tracking can be performed by first identifying interaction points thatmay belong to the same incident γ-ray, by a cluster identification method [3]. Thescattering path within a cluster is then identified by evaluating all possiblesequences of scattering points, with known source position, and finding thephysically most likely one by the evaluation of a figure of merit.

heavy elements. The response of nucleito angular momentum and temperaturewill be investigated by, for instance,ultrahigh spin states produced inextremely cold reactions, metastablestates at high spins and at very largedeformation, and multiphonon giantresonances as well as other high-temperature phenomena, such asquantum chaos.

A γ-ray tracking system involvesmeasuring the position and energy ofevery γ-ray interaction in a detector sothat the scattering path and sequentialenergy loss of each individual γ-ray canbe deduced using the Comptonscattering formula; see Figure 2. Thefull energy of the event can then bereconstructed without the losses due tosuppression shields, which coverednearly half the solid angle in theprevious generation of spectrometers.The realization of such a system willrequire highly segmented germaniumdetectors and digital electronics. Thisdevice will have wide-rangingapplications in medical imaging,astrophysics, nuclear safeguards, andradioactive waste monitoring, as wellas introducing a new plateau ofdetection capability for nuclearstructure studies.

Given the importance of thisdevelopment and its far-reachingimplications, it is not surprising thatdevelopments are taking place inEurope and in the USA to realize thisnew type of instrument. In Europe acollaboration (consisting of 40 partnersfrom over 10 countries) has alreadybeen established to construct the 4[tracking spectrometer called AGATA.This collaboration has recently signeda memorandum of understanding forthe first phase of the project to performthe research and developmentnecessary to finalize the technology forγ-ray tracking and hence fully specify

the full 4[ spectrometer. In the USA aresearch program called GRETA(Gamma-Ray Energy Tracking Array)is fully underway [2].

The AGATA project [1] is based onthe technological achievementsobtained in recent years by theEuropean γ-ray spectroscopy com-munity and especially within theEuropean TMR Network ProjectDevelopment of γ-Ray TrackingDetectors for 4R γ-Ray Arrays [4], inwhich a proof of concept for the noveltechnique of γ-ray tracking has beenachieved. In order to prove thefeasibility of a full 4[ γ-ray trackingspectrometer a demonstration of thenew technology with a subarray, the so-called AGATA demonstrator, is neededthat is sufficiently large to carry outexperiments and hence validate theconcept.

The full 4[ AGATA array will

consist of either 120 or 180 36-foldsegmented individually encapsulatedGe crystals (see Figure 3), closelypacked together in groups of three in acommon cryostat. The encapsulateddetector technology builds on thedevelopment made for the clusterdetectors of Euroball and Miniball [5].The signals from each segment as wellas from the central contact are used forthe determination of the position of theinteraction points [6, 7]. Here the shapeand size of the real charge signalcollected in one segment together withthe mirror image charges in theneighbouring segments are needed fora position resolution significantly betterthan the segment size. Note in Figure 3the difference between the physicalsegments, given by a perpendicular cutfrom the central contact to the outercontact border, and the effectivesegments, given by the real charge



Figure 3. Thirty-six-fold segmented, encapsulated Ge detector (top right). Thelower right shows the calculated effective segments, indicated by different shading.Their shape is obtained by releasing a test charge at each position in the detectorand determining on which outer segment the charge is collected. On the left, thecalculated position sensitivity in depth (l), radial (r), and azimuthal (φ) directionis indicated. The highest sensitivity is reached near the effective segmentboundaries due to the maximum of the induced signals into the neighbouringsegment.

collection geometry. The interactionposition is determined by an iterativealgorithm that compares the measuredpulse shapes with a database ofreference pulse shapes [7]. Here theparticular challenge lies in thedeconvolution of multiple interactionswithin one segment as well as real andinduced charge signals in one segment.

Research and developments isrequired to specify and investigateoptions for signal processing. Thisinvolves the use of digital electronicsand processing to extract energy, time,and interaction positions within thedetector. The energy is extracted fromthe digitized preamplifier signals usinga so-called moving windowdeconvolution (MWD) algorithm [8].The impact of the fully digitalprocessing can be seen in Figure 4. Thetop shows the raw pre-amplifier signalsat an event rate of 40 kHz. Analoguesignal processing would lead to a lowerenergy resolution due to signal pile-up.Applying the MWD algorithm extracts

clean signals, shown in the middle. Theamplitude of these signals is equal tothe collected charge. The digitalprocessing thus allows pile-up eventsto be disentangled, enabling event ratesof up to 50 kHz. The individualsegments will be triggered by the signalfrom the core contact of each crystalwhere a very low threshold can beachieved.

The AGATA collaboration aims tobuild a demonstrator subarray of up to5 detector modules, with each modulecontaining three 36-fold segmenteddetectors. The demonstrator will havea purposely built digital electronics anddata acquisition system, and thecollaboration will develop and refinethe algorithms for energy, triggering,timing, and position determination, andfor tracking. As well as proving thetracking concept and power of the fullarray, this demonstrator, which will beavailable for experiments in 2007, willbe a powerful spectrometer in its ownright.

Concluding, we would like toemphasize the enormous impact thatAGATA will have on the exploration ofnuclear structure at the extremes ofisospin, proton number, angularmomentum, and temperature. Thisradically new device will constitute adramatic advance in γ-ray detectionsensitivity that will enable the discoveryof new phenomena, which are onlypopulated in a tiny fraction of the totalreaction cross section or of nuclei thatare only produced with rates of the orderof a few per second or less. Its unpre-cedented angular resolution will faci-litate high-resolution spectroscopy withfast and ultrafast fragmentation beamsgiving access to the detailed structureof the most exotic nuclei that can bereached. Finally, the capability to operateat much higher event rates will allow thearray to be operated for reactions withintense γ-ray backgrounds, which will beessential for the study of, for example,transuranic nuclei.

References

1. AGATA Technical Proposal, J. Gerl andW. Korten, eds. (Sept. 2001).

2. K. Vetter, Nucl. Phys. News Intl. 12(2002) 15.

3. G. J. Schmid et al., IEEE-Trans. Nucl.Sci. 44 (1997) 975.

4. R. M. Lieder et al., Nucl. Phys. A682(2001) 279c.

5. J. Eberth et al., Prog. Part. Nucl. Phys.38 (1997) 29.

6. Th. Kröll, D. Bazzacco, Nucl. Instr.Meth. A 463 (2001) 227.

7. Th. Kröll et al., AIP CP 656, P. Fallon,R. Clark, eds. (2002) 357.

8. W. Gast et al., IEEE Nucl. Sci. Symp.Conf. Rec. 2, (2002) 9/182.

For the AGATA collaboration:

J. SIMPSON

CCLRC Daresbury Laboratory

R. KRÜCKEN

Technische Universität München

Figure 4. Digitized preamplifier signals for a detector rate (core signal) of 40 kHz.Top: the deconvoluted signals after using the moving window deconvolution (theenergy is obtained by averaging over the flat top of the signal (insert)). Bottom: theresponse of a triggering algorithm (Slope Condition Counting, SSC) is shown [8].




Francium Developments at Stony Brook

The radioactive element francium isof great interest in many laboratoriesbecause, as an alkali, it is the heaviestatom in which the atomic properties canpresently be calculated to better than1%. The electron–nucleus interactionsin heavy atoms are stronger than inlighter alkalis and are more sensitiveto weak interaction effects in nuclei,such as anapole moments, electricdipole moments, and other parity-violating effects. The ability to traplarge numbers of atoms, >106, wouldmake possible precision measurementsof these effects.

Stony Brook [1] and Legnaro [2]now have the capability to produce andtrap radioactive Fr produced with heavyion reactions, and experiments areplanned at KVI (Groningen) and atTRIUMF. There is also interest in usingcold atomic beams to look for atomicparity-violating effects [3].

The number of trapped atoms, N, isgiven by N=I·η·τ, where I is the initial

Fr beam intensity, η the trappingefficiency, and τ the lifetime of an atomin the trap. At Stony Brook, we initiallyworked with Fr beams of the order of105-6 Fr/sec. The lifetime of the trap isdetermined by the quality of thevacuum, with τ≈10 sec for pressures≈10-9 Torr. In our initial work, thetrapping efficiency was of the order of10-3, so we would typically have about

103-4 atoms in the trap.In the last year, a new approach to

trapping has made an order ofmagnitude improvement in the trappingefficiency [4]. Along with evolutionaryimprovements in the Fr production andvacuum, we can now trap 105 atomsroutinely, and when everything isworking optimally, should be able toachieve 106 trapped atoms. Figure 1

Figure 1. Detail of the new trappingsystem with pivoting neutralizer.

Figure 2. New Fr beam transport system.




shows the new apparatus, conceived byEduardo Gomez and constructed byGomez and Seth Aubin in ourlaboratory. The system works in“batch” mode, with Fr accumulating ona cold neutralizer for a fixed time. Afteraccumulation, the neutralizer is rotatedso that it covers the only opening in thetrapping cell, and the neutralizer is thenheated to evaporate the Fr atoms intothe cell. Because there are no exit holes,the Fr has longer to be trapped in thecell before either it is lost to a defect inthe cell coating or it finds the smallcracks around the neutralizer to diffuseout of the cell. With this system, theoverall trapping efficiency is now >1%.The “batch” nature of the trap is idealfor the planned transfer to a second trap.If the second trap has a much longerlifetime, then the number accumulatingthere will be proportional to thatlifetime, and even larger numbers ofatoms should be accumulated.

Another problem that we had withour original trapping system was thatbecause the target was located withinabout 2m of the trap, the neutronbackground precluded our working atthe trap, and everything had to beremotely controlled, or tediouslychanged by turning off the beam andentering the target room. We havesolved this problem with the new setup,which is shown in Figure 2. Theprimary 100 MeV 18O beam from theStony Brook LINAC impinges on a Autarget, which is in the shielded targetroom, while the trap and all of the lasersystems are in a separate laboratory.The Fr activity is transported as an ionbeam through a small hole in theshielding wall, and the low-energyalpha, beta, and gamma activities areeasily shielded in the trapping area.

The target is heated by the beam andby an auxiliary heater to just below themelting point for fast diffusion of the

Fr to the Au surface, where it is emittedas an ion. By adjusting the beam power,we can melt the target, but for longerlife of the target, we generally work justbelow the melting point. We haveobserved the melting with a CCDcamera, since the emissivity of theliquid is about 5% higher than that ofthe solid. There is a corresponding largeincrease in the Fr beam because of theenhanced diffusion in the liquid.

The ions are transported at 5 keV inthe all-electrostatic beam line. Thetransport is mass independent, so thatwe can tune everything with a Rb+ beamgenerated by spraying Rb atoms ontothe hot Au target, or from the inevitableimpurity alkali atoms present in eventhe highest purity Au.

Seth Aubin has led the effort to testthe new trapping system by measuringlifetimes and hyperfine structure in the9s state [5]. These measurements testthe ability of the ab-initio atomiccalculations to predict matrix elementssimilar to the ones that are needed forinterpreting PNC measurements.Figure 3 shows the energy levelsrelevant to the measurement. We useda sequence of laser pulses at differentwavelengths to move a large fractionof the population of the atoms in the

trap into the 9s state. With all of thelasers switched off, we then detectedthe decay of the state with aphotomultiplier and an 851nminterference filter. The measuredlifetime is compared with theory inFigure 4. The agreement with the ab-initio theories is remarkable, wellwithin the uncertainty of the theory.

The hyperfine interaction constantis also an important testing ground forab-initio atomic calculations of Fr.While the nuclear g-factor has beenpreviously measured with a precisionof 2%, a more precise measurement isnecessary for testing the atomic wavefunctions that are used for weakinteraction measurements in Fr. Wepropose to measure the nuclear g-factorwith Fr+ ions, in which the much largerelectron magnetic moment is removed.We are developing an apparatus, similarin concept to the TRIUMF polarized Libeam: We start with a Fr+ beam,neutralize it, polarize it by opticalpumping, and then re-ionize the atomsto form a polarized Fr+ beam. We willthen slow, cool, and confine the ions inan ion trap. We will measure the nuclearmagnetic moment to high precision byresonantly destroying the spatial

Figure 3. Energy levels of Fr and laserwavelengths for exciting the 9s state.

Figure 4. Comparison of measuredlifetime with theoretical predicationsfrom radial matrix elements: (a)6, (b)7,(c)8.

anisotropy of the alpha-particle decaydistribution.

The g-factor measurement appara-tus is presently under construction. Theneutralization step has been success-fully accomplished with Rb vapor as aneutralizer. We simultaneously injectedboth a Rb+ beam and a much weakerFr+ beam through a Rb vapor anddetermined the Rb ion/atom ratio bymeasuring the Rb+ ion current inFaraday cups before and after the vaporregion. The Fr ion/atom ratio wasdetermined by stopping the Fr beam infront of an alpha-particle detector anddeflecting the Fr+ ions after the vapor

region with a transverse electric field.With this system, we have establishedthat the charge exchange cross sectionfor Fr+ + Rb is larger than thecorresponding cross section for Rb+ +Rb, and 90% of Fr+ are neutralized with4cm of Rb vapor at T≈115ºC with atomdensity of 1.5 x 1013/cm3.

Acknowledgments

E. Gomez is supported byCONACYT, Mexico. This work hasbeen supported by NSF. L. A. Orozcohas recently moved to the Universityof Maryland but will continue the Frresearch program at Stony Brook.


Figure 5. Schematic diagram of apparatus to trap polarized Fr atoms.

References

1. J. E. Simsarian, A. Ghosh, G. Gwinner,L. A. Orozco, G. D. Sprouse, and P. A.Voytas., Phys. Rev. Lett. 76 (1996)3522–3525.

2. S. N. Atutov, V. Biancalana, A.Burchianti, R. Calabrese, L. Corradi, A.Dainelli, V. Guidi, B. Mai, C. Marinelli,E. Mariotti, L. Moi, E. Scansani, G.Stancari, L. Tomassetti, S. Veronesi.,Physica Scripta T105 (2003) 15–18.

3. S. Sanguinetti, J. Guena, M. Lintz, P.Jacquier, A. Wasan, M. A. Bouchiat.,Eur. Phys J. D 25(1) (2003) 3–13.

4. S. Aubin, E. Gomez, L. A. Orozco, andG. D. Sprouse, Rev. Sci. Instr. (2003).

5. S. Aubin, E. Gomez, L. A. Orozco, andG. D. Sprouse., Optics Letters (2003).

6. M. S. Safronova, W. R. Johnson, andA. Derevianko, Phys. Rev. A 60 (1999)4476.

7. V. A. Dzuba and V. V. Flambaum,School of Physics, University of NewSouth Wales, Sydney, New SouthWales2052, Australia (personal communi-cation, 2003).

8. M. Marinescu, D. Vrinceanu, and H. R.Sadeghpour, Phys. Rev. A 58 (1998)R4259.

S. AUBIN, E. GOMEZ, K. GULYUZ,L. A. OROZCO, J. SELL,

AND G. D. SPROUSE

State University of New York,Stony Brook



impact and applications

Selected Isotope Applications in Cosmochemistry

and Geochemistry

Abstract

Today, isotope techniques are afirmly established tool in both geo-chemistry and cosmochemistry. Aplethora of dating techniques is nowroutinely used, chosen to suit thetimescale of the process being investi-gated, existing instrumentation, andavailability of appropriate samples [1].Nevertheless, the age provides only thetimeframe for other isotopic inform-ation such as material origin andprocess(es) recorded by the variousisotope systems. We illustrate this herewith some topical examples frominterstellar grain cosmochemistry andstudies of early Earth geochemistry.

Introduction

Geochemistry has its rootsentangled both in the economic needto identify ore minerals and the questto understand the origin of the worldwe live in. The latter has had arguablythe greatest impact on our under-standing of geological processes, withresulting huge economic benefitsprovided almost as a sideshow. Ourfascination with the Earth and itsgeology encompasses the more obviousearthquakes, volcanoes and dinosaurs,as well as the more esoteric, such asthe structure and evolution of the core,silicate mantle, continental crust, andocean/atmosphere system. Indeed, withmuch current emphasis on environ-mental issues, the impact and controlof the geological system on ourimmediate surroundings has establish-ed geochemistry as an interface sciencewith atmospheric chemistry, climat-ology, oceanography, hydrology, and

many other related disciplines.Isotope cosmochemistry provides

another interface, providing an insightinto the basic element buildingprocesses in stars and how this materialis captured, accreted, and processed toform the planets that we see or standon today. A quick inventory of even themost well-known sample resourcesreveals huge variety and scale, e.g.,solar wind; micron-sized interstellargrains; interplanetary dust particles;Martian, lunar, and asteroid meteorites;and lunar sample return, and alsoillustrates how nuclear physics,astrophysics, and cosmochemistry arestrongly intertwined. To cover all facetsof isotope geochemistry and cosmo-chemistry would require severaltextbooks. We present below just a fewareas in isotope geochemistry andcosmochemistry that exemplify theapplication of isotopes in the study ofwidely different areas and availablesample resources.

Interstellar Grains

It is well known that astronomersstudy photons from the whole range ofthe electromagnetic spectrum to try andunderstand violent astrophysical andnucleosynthetic events ranging fromstar formation to the death of galaxies.What is perhaps not quite so wellknown is that over the last two decades,meteoriticists have discoveredinterstellar grains from these extremeenvironments existing almost unalteredin meteorites and have developed waysof isolating them for study [2–4].Astronomical observations of extremephenomena such as supernovae are

crucial to help improve our under-standing of nuclear and astrophysicaltheory, but how advantageous to alsohave solid condensates from thoseevents available for study in thelaboratory! Grains from supernovae,novae, Wolf-Rayet, and giant stars havebeen isolated and identified and thestudy of their isotopic patterns for awhole range of elements now drivesastrophysical and nuclear theory inthese extreme conditions [5]. The studyof interstellar grains can be used to inferinformation in areas of stellar dynamicsthat cannot be probed by any othermeans, for example, obtaining manynuclear cross-sections, precise isotopiccompositions within stars, the numberof stellar sources contributing to theformation of the solar system, andimplications for galactic chemicalevolution and the age of the galaxy. Itcan also complement astronomicalspectral observations of stars byproviding an additional source ofinformation for the isotopic compo-sition within stars and information onthe physical and chemical conditionswithin stellar atmospheres. Interstellargrain studies also have the potential toconstrain conditions during theformation of the solar system and theenvironment and method of capturewithin their parent meteorite bodies.

The grains of silicon carbide,graphite, and corundum themselvesthough are typically micron sized, andmeasuring accurate isotope ratios of arange of elements in such tiny sampleschallenges the capabilities of modernanalytical instruments. Nevertheless,the scientific potential is huge as the

discovery of actual condensates from atime early in galactic history and fromobjects as extreme as supernovae givesus a new window on the universe, ifonly we can see through micron-sizedpanes. The key to understanding theirhistory lies in the analysis of theirisotope ratios.

Isotopic analysis, however, requiresmass spectrometry and therefore thedestruction, or certainly damage, of thesample. Much of the development ofinstruments such as noble gas massspectrometers, as well as high-spatial-resolution electron, laser, and ionprobes, has therefore been driven by theneed to analyze the absolute minimumquantity of material possible. Aninterstellar grain 1 micron in diametercontains only about 1011 atoms in totalwith abundances of rarer elements andisotopes running right down to “a fewatoms.” The spatial resolution andsensitivity required to work withinthese constraints are now being met bysecondary ion mass spectrometers,which focus ion beams down to 50 nm,producing secondary ions for analysisor using lasers to ionize the sputteredatoms [6–8]. Achievements in this fieldare now the construction of 50 nmresolution isotope maps of micron-sized grains with very high sensitivity(Figure 1). The spin-offs of thesedevelopments are widely applicable tomany other areas where samples aresmall and isotope ratios are required.

Nuclear Astrophysics

With rare exceptions, the isotoperatios of any element vary compar-atively little on the Earth, usually withina few percent or so at the most.However, in interstellar grains theisotope ratios in common elements suchas carbon, nitrogen, and oxygen canvary by up to four orders of magnitudeand silicon by one order of magnitude

(indeed, this is the primary evidence toidentify them as interstellar). 12C, 14N,and 16O participate in CNOnucleosynthesis in massive stars, withonly minor reactions producing theother stable isotopes of these elements:13C, 15N, and 17,18O. Thus within amassive star, the major/minor isotoperatio can vary enormously dependingupon depth and temperature. In theheavier elements, the pattern of “s”process nucleosynthesis has beenclearly seen and isotope abundancesgenerally agree with theoreticalpredictions. Expected patterns of “r”process nucleosynthesis have not beenseen in interstellar grains, however, andthis is a major puzzle [4].

Big bang nucleosynthesis producedH, He, and some 7Li. All other elementshave been synthesized since that timein massive stars and ejected into the

interstellar medium to seed new starformation with heavier elements. Thus,over the lifetime of the universe, thechemical composition of average stellarmaterial has become progressivelyenriched in heavier elements. (Onlymassive stars have contributed to thisgalactic chemical evolution since theyare short-lived [<109 years] and so caneject substantial material back into theinterstellar medium, unlike stars suchas the sun.) Exothermic fusion reactionssynthesize lighter element isotopes, andthis combined with models of neutroncapture in supernovae may be able toaccount quite accurately for theobserved abundances of elements up tothe iron group elements. Above thatmass, isotopes are synthesized byneutron capture. If the neutron flux issufficiently high that successivecaptures occur on a timescale that is


Figure 1. Time-of-flight secondary ion mass spectrometer with laser ionizationcurrently being built at Manchester (“IDLE” = Interplanetary Dust LaserExplorer). Design aims are 50 nm spatial resolution, 157 nm laser post-ionizationfor high-detection sensitivity, and a mass resolving power >3000 to enable isotopicanalyses of many elements in interstellar grains.



short compared to the β decay lifetimeof the capturing isotope, thenincreasingly neutron-rich isotopes willform. If the neutron capture rate is lowcompared to the β decay lifetime of thecapturing isotope, then production ofthe same mass isotope of the elementof 1 larger atomic number will result.Photon-induced reactions can produceneutron-poor isotopes of manyelements. The general theory of “r,”“s,” and “p” process nucleosynthesis,as these are known, respectively, hasbeen worked out in some detail overthe last 50 years [9], but thenucleosynthetic sites are still not known[9,10]. There are many excellentreviews of this area, such as [9], thatdeal with this topic far more rigorouslythan space allows here, but the detailsare still sufficiently challenging that arecent report from the NationalAcademy of Sciences included “Howare the elements from iron to uraniumsynthesized?” as one of 11 majorunanswered questions facing modernastrophysics for the new century,ranked alongside such questions as“What is dark matter?” and “What isthe nature of dark energy?” [11].

The Oldest Rocks, Early Oceans,

and Life

The impact of instrument deve-lopment on terrestrial studies is equallygreat, but very much focused onobtaining age information and preciselyresolving the much smaller isotopicdifferences that provide informationabout material origin or processes thathave operated in the past. Identifyingthe conditions existing on the very earlyEarth is difficult because almostnothing is left in the geological record.Much evidence is inferred from isotopicchanges that can only have been causedby these early conditions. For example,while the oldest preserved microfossils

are 3.5 Ga, carbon isotopic com-positions that can only be caused bybiological process are preserved insamples as old as 3.8 Ga [12]. Morerecently, high-resolution ion probeswith a spot size of 20–25 µm diameterhave recently enabled zircon fragmentsto be dated at 4.404±0.008 Ga—theoldest terrestrial samples yet found[13]—and close to the age the Earthformed (4.55 Ga). Importantly, theoxygen isotopic composition of thesesamples can only have come from anenvironment containing liquid water[13,14]. These latest results suggest thatthe conditions for development of lifeon Earth may have existed as much as600 Ma before the earliest isotopicrecord of life.

A clue to why life took so long togain a foothold is found in the crateringrecord of the moon that shows a late(3.8–4.0 Ga) heavy meteorite bombard-ment. Evidence for this also affectingthe Earth is found by examining thetungsten isotope composition of someof the earliest metamorphosedsediments found in Greenland (3.7–3.8Ga). These record a 182W anomaly, thedecay product of 182Hf (t1/2 = 9Ma), onlyfound in meteorites, and show that thesesediments have incorporated a signif-icant raw meteorite component [15].

The Structure of the Earth and Its

Chemical Evolution

Perhaps one of the most importantchanges in our understanding of theway the Earth continued to evolve hasoccurred only over the previous 6–7years. For the last 25 years geochemistshave argued successfully that theEarth’s silicate mantle is chemicallylayered and that only 30–50% by massof the mantle has played any role incontinental crust and atmosphereformation. This separation has beenattributed to the endothermic phase

change that occurs in the mantle at 670km depth, retarding or even preventingmass transfer across this boundary.New high-resolution seismic images ofdensity contrasts in the mantle clearlyshow cold dense oceanic crust beingsubducted under the continents andsinking through the 670 km boundary,possibly to the core mantle boundary[16]. Combined with recent advancesin numerical models of convection(Figure 2) that have incorporated theisotopic evolution of volatile tracers inthe mantle (3He/4He), these resultssuggest that the mantle should in factbe well mixed and not layered [17,18].Why do geochemical and geophysicalapproaches predict such apparentlyirreconcilable differences in theirmodels for the Earth’s internal structureand therefore its chemical evolution?

Samples from the mantle come fromtwo different sources. Mid-ocean ridgesextend some 65,000 km around theglobe and form the source for newoceanic crust and provide material fromthe uppermost mantle. Ocean islands“hotspots” or “plumes,” such as Hawaiiand Iceland, probably sample muchdeeper portions of the mantle system.Compositional and isotopic differencesexist between these different sampletypes that require the existence ofdifferent and long-lived geochemicalreservoirs in the mantle. The mid-oceanridge material is derived from a sourcethat has been degassed and depleted inits crust-forming elements. Oceanicislands in contrast tap a reservoir thatin part looks like oceanic crust that hasbeen subducted and isotopicallyevolved (e.g., 147Sm→143Nd, 87Rb→87Sr,235,238U→207,206Pb) in the mantle for 1–2Ga [19]. Another component of theocean island material has never beeninvolved in surface process. This isshown by its high accretionary volatilecontent inferred from 3He/4He ratio


determinations (see [18]). This tracercan be used confidently because thereis no significant production of 3He inthe mantle, while U and Th decaydominate the 4He inventory. 3He/4He istherefore a good proxy for the accre-tionary volatile to solid ratio. It is worthnoting that predicted accretionaryvalues of 3He/22Ne are found in theEarth’s mantle—occasional advocatesof nuclear processes producing mantle

3He such as natural critical massreactors or cold fusion must alsoaccount for this relationship.

While recent modeling approacheshave increased the number of degreesof freedom by introducing additionalbut seismically invisible densitycontrasts into the model mantle system,the reconciliation of geophysicalobservation and fluid dynamicalmodels with geochemical observations

has yet to be achieved [20]. The role ofthe geochemist must be to find evidencefor early earth processes and conditionsthat would support or refute suchconcepts. One promising way toaddress this puzzle is to try tounderstand the conditions that wouldenable the high accretionary volatileconcentrations recorded by the 3He/4Hein the deep mantle samples to betrapped in the Earth’s interior. This iseffectively an attempt to understandwhat happened in that missing 100 Mabefore the first surface water on Earthwas present.

Noble Gases, CO2-Rich Natural

Gas, and the Origin of Volatiles in

the Earth

Noble gas isotopes such as 3He/4He(but also Ne, Ar, and Xe isotopes) are avery powerful tool used acrosscosmochemistry and geochemistry[21]. Their particular advantage lies notonly in their chemical inertness, greatlysimplifying interpretation, but also intheir very low abundance in mostnatural samples. The latter propertymeans that small isotopic additionsfrom background nuclear processes aresimple to identify and quantify.Although a lot of noble gas work hasfocused on samples from mid-oceanridges or hot spots, CO

2-rich natural

gases derived from the mantle occur inmany continental regions [22]. Inparticular, a CO

2 natural gas sample

from New Mexico recorded the firstobserved terrestrial excess 129Xe/132Xe[23], clearly showing that ageochemical reservoir within the Earthhas preserved a separate record of early129I activity (t1/2 = 17Ma). This andsubsequent results provide importantevidence that this part of the mantle lostmuch of its volatile inventory to theatmosphere while 129I was still active,in the first 80 Ma of the Earth’s history



Figure 2. Numerical simulations of mantle convection [17] show plumes risingfrom the core mantle boundary and cold material that subducts and remixes backinto the mantle. Note the deflection of both plumes and subducting/sinking materialat a common depth. This is due to the Si, which occupies the tetrahedral site inthe shallow mantle, undergoing a phase transition at 670 km depth to a structurewith intrinsically denser packing (octahedral coordination). Although this phasetransition is endothermic and slows down mass transfer, it does not result in thechemical isolation of different “layers” within the mantle, previously thought toaccount for the difference in the isotopic signatures of samples from mid-oceanridges (upper mantle) and hotspots (deep mantle).


(see [20]).But how were the volatiles

incorporated into the mantle in the firstplace? Two currently competingmodels respectively advocate (i)equilibration between the moltenaccreting planet and a massive earlyatmosphere, not too dissimilar to whatwe see surrounding gas giants today;and (ii) volatiles trapped withinaccreting material being carried into theEarth’s deep interior. Neon isotopesmay provide the answer [24] (Figure3). A massive early atmosphere would


have a Solar Ne isotopic composition(20Ne/22Ne=13.8) while accretingmaterial that has been irradiated bysolar wind preserves a distinctcomposite mix, often called Ne-B(20Ne/22Ne=12.5). To date the highestreliable Ne isotopic values measured inmid-ocean ridge basalt samples reacha maximum at values of about 12.5, butit is not possible to rule out thepossibility that ubiquitous aircontamination (20Ne/22Ne=9.8) found inthis sample type suppresses themaximum Ne value measured [25].

Although natural CO2-rich gases are

also subject to air contamination, in afew fields this is very small. Indeed,recently samples from the same gasfield that showed the first 129Xe/132Xeanomaly have been used to identify asolar-like 124-128Xe/132Xe component[26] and is the first indication that theconvecting mantle may have evolvedby equilibration between a solar-likeearly massive atmosphere rather than atrapped composition. Detailed inves-tigations of the Ne isotopes from thissample resource are currently underwayin Manchester and will provide animportant piece in the early Earthjigsaw.

References

1. Halliday A. N. (1997). Radioactivity, thediscovery of time and the earliest historyof the Earth. Contemporary Physics 38,103–114.

2. Amari, S., Lewis, R. S., Anders, E.(1994). Interstellar grains in Meteorites:I. Isolation of SiC, graphite, anddiamond; size distributions of SiC andgraphite. Geochim. Cosmochim. Acta58, 459–470.

3. Nittler, L. R. (2003). Presolar stardustin meteorites: recent advances andscientific frontiers. Earth and Planet.Sci. Lett. 209, 259–273.

4. Ott, U. (2001). Presolar grains inmeteorites: An overview and someimplications. Planetary and SpaceScience 49, 763–767.

5. Bernatowicz, T. and Zinner, E. (Eds.).(1997). Astrophysical consequences ofthe laboratory study of presolarmaterials. AIP Proceedings 402, AIP,Woodbury, New York (and referencestherein).

6. Hoppe, P. (2002). NanoSIMS perspec-tives for nuclear astrophysics. NewAstronomy Reviews 46, 589–595.

7. Stephan, T. (2001). TOF-SIMS incosmochemistry. Planetary and SpaceScience 49, 859–906.

8. Nicolussi, G. K., Pellin, M. J., Lewis,R. S., Davis, A. M., Amari, S., andClayton, R. N. (1998). Molybdenum

Figure 3. The Ne isotopic composition predicted for a massive early atmosphereis Solar. Solar Ne trapped in meteorites is a mixture of mass fractionated (MFL),solar flare—related Ne (SEP), and solar wind, giving an average compositioncalled “Ne-B”. This distinction may provide an opportunity to distinguish betweendifferent models of volatile input into the Earth’s mantle (see text). To date, theupper 20Ne/22Ne limit recorded in ocean island samples (deep mantle) and at mid-ocean ridges (upper mantle) is compromised by ubiquitous air/seawatercontamination of samples on eruption. Both sample sets have 21Ne in excess ofsolar Ne values due to 18O(a,n)21Ne production in the mantle. The volatile, rich,deep mantle is less deflected by this production than the more degassed uppermantle.

isotopic composition of individualpresolar silicon carbide grains from theMurchison meteorite. Geochim.Cosmochim. Acta 62, 1093–1104.

9. Arnould, M., and Takahashi, K. (1999).Nuclear Astrophysics. Rep. Prog. Phys.62, 395–464

10. Sneden, C., Cowan, J. J., Ivans, I. I.,Fuller, G. M, Burles, S., Beers, T. C.,and Lawler, J. E. (2000). Evidence ofmultiple r-process sites in the earlygalaxy: New observations of CS22892-052. Astrophys. J. 533, L139–L142

11. Connecting quarks with the cosmos:eleven science questions for the newcentury (2002). Report of Committee onthe Physics of the Universe, NationalAcademy of Science, NationalAcademies Press.

12. Mojzsis, S. J., Arrhenius, G.,McKeegan, K. D., Harrison, T. M.,Nutman, A. P., and Friend, C. R. L.(1996). Evidence for life on earth before3,800 million years ago. Nature 384,55–59.

13. Wilde, S. A., Valley, J. W., Peck, W. H.,and Graham, C. M. (2001). Evidencefrom detrital zircons for the existenceof continental crust and oceans on theEarth 4.4 Gyr ago. Nature 409, 175–178.

14. Mojzsis, S. J. and Arrhenius, G. (1998)Phosphates and carbon on Mars:Exobiological implications and sample



return considerations. J. Geophys. Res.Planets 103, 28495–28511.

15. Schoenberg, R., Kamber, B. S.,Collerson, K. D., and Moorbath, S.(2002). Tungsten isotope evidence fromsimilar to 3.8-Gyr metamorphosedsediments for early meteoritebombardment of the Earth. Nature 418,403–405.

16. van der Hilst, R. D., Widiyantoro, S.,and Engdahl, E. R. (1997). Evidence fordeep mantle circulation from globaltomography, Nature 386, 578–584.

17. van Keken, P. E. and Ballentine, C. J.(1999). Dynamical models of mantlevolatile evolution and the role of phasetransitions and temperature-dependentrheology. J. Geophys. Res. Solid Earth104, 7137–7151.

18. Ballentine, C. J., van Keken, P. E.,Porcelli, D., and Hauri, E. H. (2002).Numerical models, geochemistry andthe zero paradox noble-gas mantle. Phil.Trans. R. Soc. Lond. A 360, 2611–2631.

19. Hofmann A. W. (1997). Mantlegeochemistry: The message Fromoceanic volcanism. Nature 385, 219–229.

20. Porcelli, D., and Ballentine, C. J. (2002).Models for the distribution of terrestrialnoble gases and evolution of theatmosphere. Rev. Min. Geochem. 47,411–480.

21. Porcelli, D., Ballentine, C. J., and

Wieler, R. (Eds.). (2002). Noble gasgeochemistry and cosmochemistry.Mineralogical Society of America,Washington, DC.

22. Ballentine, C. J., Schoell, M., Coleman,D., and Cain, B. A. (2001) 300-Myr-oldmagmatic CO2 in natural gas reservoirsof the west Texas Permian basin. Nature409, 327–331.

23. Butler, W. A., Jeffery, P. M., Reynolds,J. H., and Wasserburg, G. J. (1963).Isotopic variations in terrestrial xenon.J. Geophys. Res. 68, 3283–3291.

24. Trieloff, M., Kunz, J., Clague, D. A.,Harrison, D., and Allegre, C. J. (2000).The nature of pristine noble gases inmantle plumes. Science 288, 1036–1038.

25. Ballentine, C. J., Porcelli, D., andWieler, R. (2001). Technical commenton “Noble gases in mantle plumes” byTrieloff et al. (2000). Science 291,2269a.

26. Caffee, M. W., Hudson, G. U., Velsko,C., Huss, G. R., Alexander, E. C., andChivas, A. R. (1999). Primordial noblegases from Earth’s mantle: Identi-fication of a primitive volatilecomponent. Science 285(5436), 2115–2118.

CHRIS J. BALLENTINE

IAN LYON

University of Manchester


meeting reports

Symmetries in Nuclei, Erice, March 23–30, 2003

The Highly Specialized Seminar on“Symmetries in Nuclear Structure” washeld at the Ettore Majorana Centre inErice, Italy, March 23–30, 2003. Themeeting was intended to celebrate, onthe occasion of his 60th birthday, thecareer and the remarkable achieve-ments of Francesco Iachello. Since thedevelopment of the Interacting BosonModel in the early 1970s, the ideas ofFrancesco Iachello have provided avariety of frameworks for under-standing collective behaviour in nuclearstructure, founded in the concepts ofdynamical symmetries and spectrumgenerating algebras. The original ideas,which were developed for thedescription of atomic nuclei, have nowbeen successfully extended to coverspectroscopic behaviour in other fields,such as molecular or hadronic spectra.More recently, the suggestion byIachello of critical point symmetries totreat nuclei in shape/phase transitionalregions has opened an exciting newfront for both theoreticians andexperimentalists.

The meeting gathered more than 80people from 20 countries. With a fewexceptions that were due to a largeextent to the sudden worsening of theinternational situation in the MiddleEast, all the individuals who havecontributed to the field were present forthe reunion, showing their scientific andpersonal gratitude to Francesco Iachellofor the important role played by hisseminal work in the whole field ofnuclear research.

The talks presented at the meeting

covered many of the most activeforefront areas of nuclear structure aswell as other fields where ideas ofsymmetries are being explored. Topicsin nuclear structure included extensivediscussions of dynamical symmetries,critical point symmetries, phasetransitions, statistical properties ofnuclei, supersymmetry, mixed sym-metry states, shears bands, pairing andclustering in nuclei, shape coexistence,exotic nuclei, dipole modes, andastrophysics, among others. Animportant session focused on talks byEuropean Laboratory Directors (or theirrepresentatives) outlining futureprospects for nuclear structure, whileother sessions were devoted to theapplication of symmetry ideas to

molecular phenomena and to hadronspectroscopy. Finally, special lecturesby Nobel Laureate Alex Mueller, on sand d wave symmetry in supercon-ductors, and by Antonino Zichichi, onsupersymmetry in particle physics,presented unique insights into alliedfields.

Erice and the Ettore MajoranaCentre provided an ideal venue for themeeting. The location fit perfectly withthe spirit of the reunion, since preciselyin this place so many of the earlysuccesses of the interacting bosonmodel were announced in the late 1970sto early 1980s.

ANDREA VITTURI

Universita’ di Padova, Italy

Francesco Iachello (left), with Alex Mueller (center) and Antonino Zichichi (right).

meeting reports

International Symposium on Physics of Unstable Nuclei

The symposium program covered awide range of topics on the physics ofunstable nuclei, which are grouped inthe three following areas:

1. Structure of unstable nucleipresented the latest experimentalresults on exotic nuclei, nuclearclusters and molecules, superheavynuclei, as well as the application ofthe shell model, relativistic meanfield theory, quasi-particle random-phase approximation and otherstructure models to study unstablenuclei.

2. Nuclear reactions induced by exoticbeams included the excitation andbreakup of exotic nuclei, elastic andinelastic scattering, transfer andcharge exchange reactions, fusionand fission, and isospin distillationin heavy-ion collisions.

3. Nuclear astrophysics discussedlow-energy nuclear reactions withexotic beams, nucleosynthesis,asymmetric nuclear matter andsupernova neutrinos.

During the six days of thesymposium we had many excellentpresentations of new results in thephysics of unstable nuclei as well as

The International Symposium onPhysics of Unstable Nuclei (ISPUN02)was held at Halong Bay (Vietnam) onNovember 20–25, 2002. It was thesecond large-scale internationalmeeting on basic nuclear physics andthe first topical symposium on physicsof exotic nuclei ever held in Vietnam.The symposium was organized jointlyby the Institute for Nuclear Science andTechnique (INST) and the Institute ofPhysics based in Hanoi, under thesponsorship of the Institute of Physicaland Chemical Research (RIKEN,Japan), the Natural Science Council ofVietnam, and the Vietnam AtomicEnergy Commission.

In total, more than 120 participantsfrom 18 countries on four continentsattended the symposium. We werepleased to have, among them, manyworld experts in the field and a goodnumber of young researchers. Thescientific program consisted of 98 talks,which were presented in nine plenaryand four parallel sessions. The plenarysessions included several reviews andoral presentations of the latest resultsin both theoretical and experimentalstudies of unstable nuclei. The parallelsessions were devoted to specializedtalks and short oral presentations.

lively discussions about the openquestions and challenges, and thesymposium has been very beneficial tomany participants, in particular to theyoung researchers and students fromuniversities and institutions in Vietnam,many of whom were attending aninternational meeting in nuclear physicsfor the first time. ISPUN02 has beenrated by many colleagues as a verysuccessful attempt to promote basicscience in Southeast Asia.

Last but not least, this symposiumwas also a good opportunity for thenuclear physicists of the internationalcommunity, especially those visitingVietnam for the first time, to discovernot only the beauty of the country’slandscape but also the hospitality of theVietnamese people.

DAO TIEN KHOA

VO VAN THUAN

INST Hanoi

NGUYEN DINH DANG

RIKEN and INST Hanoi

SHIGERU KUBONO

CNS Tokyo

NGUYEN VAN GIAI

IPN Orsay



David B. Fossan

obituary

matured in the last few years with thediscovery of chiral doublet structures inodd-odd nuclei, in which right- and left-handed triaxial nuclei were shown to havea nearly degenerate set of energy levels.The presence of such mirror nuclei hadbeen hitherto unknown, and theirobservation opens new avenues of studyof the role of symmetries in nuclearstructure.

In the national arena, Fossan playeda variety of important roles. In additionto his leadership in the gammasphereproject, he served on advisory committeesat Brookhaven National Laboratory, theIndiana Cyclotron Facility, LawrenceBerkeley National Laboratory, Oak RidgeNational Laboratory, and ArgonneNational Laboratory. He held guestappointments at Brookhaven Lab, theUniversity of Munich, LawrenceBerkeley Lab, and Chalk River NuclearLaboratory. He served as a member ofthe Editorial Board for Physical ReviewC, and as chair of the 1987 GordonConference on Nuclear Chemistry.

Fossan was an exceptional mentor foryoung scientists. He supervised the thesisresearch of over 20 Ph.D. students and16 postdocs who have gone on tooutstanding careers in physics, medicalphysics, and other areas. Although he setrigorous standards, David’s energy,enthusiasm, and dedication helped himprovide an unparalleled learningenvironment for students. He gavestudents real responsibility and demandedthat they produce, but offered advice ateach step along the way. He wasenormously generous with his time, goingfar out of his way to work with studentsin the laboratory and in the classroom.

David’s affability and good naturemasked a deep competitive drive. Someof this came out through the demands heplaced upon himself to extend the

David B. Fossan

David B. Fossan, a world leader instudies of nuclear structure and propertiesof exotic states of nuclei, died July 27,2003 following a heart attack thatoccurred while swimming at LongIsland’s south shore. He was on theannual beach outing he organized for hisresearch group. Dave was a professor ofphysics at the State University of NewYork at Stony Brook, where he had beenon the faculty since 1965.

Fossan was born in Faribault,Minnesota in 1934. He received his B.A.from St. Olaf College in Minnesota in1956 and his Ph.D. from the Universityof Wisconsin in 1960 under the directionof Prof. Heinz Barschall. Before joiningthe Stony Brook faculty, he held apostdoctoral appointment at the NielsBohr Institute at the University ofCopenhagen (1961–1962) and LockheedCorporation (1963–1964).

On joining the young department atStony Brook in 1965, David was a chartermember of the new Nuclear StructureLaboratory. His research has been thecornerstone of the Laboratory’s programuntil today. His research program wasremarkable both for its breadth of focusand its productivity, with over 260publications. He returned many times toseveral themes for exploring nuclei inextreme conditions as new techniques andtheories opened new avenues. Fossan wasa Fellow of the American PhysicalSociety, held a Humboldt U.S. SeniorScientist Award in 1989, and in 2002received the State University of New YorkChancellor’s Award for Excellence inResearch in the first year of the award’sexistence.

Fossan was a leading player inestablishing the gammasphere detectorand served on its steering committee frominception of the project until 1996.Fossan’s earlier studies of nuclear shapes

understanding of physics, but an evenmore apparent manifestation was hisathletic drive. His early love forbasketball transformed in later days tofrequent rounds of tennis, during whichhe would put away the opposition with asmile on his face.

We will remember David Fossan forhis many contributions to our understand-ing of the complex processes at work inlarge and exotic nuclei. His experimentalskills, coupled with his deep understan-ding of the quantum basis for multi-particle systems, distinguished his re-search career. Even more, we will remem-ber him for his outstanding personalcontributions to generations of physicists,his fierce honesty, his remarkablecheerfulness, and his deep commitmentto bringing out the best in others.

ROBERT L.MCGRATH AND GENE D. SPROUSE

State University of New York

news from EPS/NPB

Call for Nominations for the Lise Meitner Prize

for Nuclear Science

rities in the field that outline the impor-tance of the work would also be helpful.

Nominations will be treated inconfidence, and although they will beacknowledged, there will be no furthercommunication. Nominations shouldbe sent to:

Selection Committee LM PrizeChairman Prof. Ronald C. JohnsonDepartment of PhysicsSchool of Physics and ChemistryUniversity of SurreyGuildford, Surrey,GU2 7XH, United Kingdom

Phone: +44 (0)1483 879375Fax: +44 (0)1483 876781E-mail: [email protected]

To download a nomination form andfor more detailed information, see thewebsite of the Nuclear PhysicsDivision, http://www.kvi.nl/~eps_npand the website of EPS, www.eps.org(EPS Prizes, Lise Meitner Prize)

The deadline for the submission ofthe proposals is January 10, 2004.

The Nuclear Physics Board of theEPS invites nominations for the year2004 for the “Lise Meitner Prize.” Theaward will be made to one or severalindividuals for outstanding work in thefields of experimental, theoretical, orapplied nuclear science. The Boardwould welcome proposals thatrepresent the breath and strength ofEuropean nuclear sciences.

Nominations should be accom-panied by a completed nominationform, a brief curriculum vitae of thenominee(s), and a list of major pub-lications. Letters of support from autho-

Call for Nominations for the IBA-Europhysics Prize

2004 for Applied Nuclear Science and Nuclear Methods

in Medicine

The Nuclear Physics Board of theEPS invites nominations for the year2004 for the IBA-Europhysics prize.The award will be made to one orseveral individuals for outstandingcontributions to applied nuclear scienceand especially to nuclear methods andnuclear research in medicine.

The Board welcomes proposals thatrepresent the breadth and strength ofapplied nuclear science and nuclearmethods medicine in Europe.

Nominations should be accom-panied by a completed nominationform, a brief curriculum vitae of thenominee(s), and a list of major publica-

tions. Letters of support from autho-rities in the field which outline theimportance of the work would also behelpful.

Nominations will be treated inconfidence and although they will beacknowledged there will be no furthercommunication. Nominations shouldbe sent to:

Selection Committee IBA PrizeChairman Prof. Ch. Leclercq-WillainDepartment of Theoretical NuclearPhysics–PNTPM–CP 229

Université Libre de BruxellesBvd du Triomphe,B1050 Bruxelles, BelgiumPhone: +32 (0)26505560Fax: +32 (0)26505045E-mail: [email protected]

To download a nomination form andfor more detailed information, see thewebsite of the Nuclear PhysicsDivision, http://www.kvi.nl/~eps_npand the website of EPS, www.eps.org(EPS Prizes, IBA-Europhysics Prize)

The deadline for the submission ofthe proposals is January 10, 2004.


2004January 11–17

Hirschegg, Kleinwalsertal, Austria.

Electromagnetic Interactions in

Nuclei and the Nucleon. International

Workshop XXXII on Gross Properties

of Nuclei and Nuclear Excitations.

Contact: G. Kluckner, Tel.: +49-6151-16-3073. Fax: +49-6151-16-6076. E-mail: [email protected]

Web: http://crunch.ikp.physik.tu-darmstadt.de/nhc/pages/e v e n t s / h i r s c h e g g /HirschAn2004.html

January 11–17

Oakland, CA, USA. Quark Matter

2004. Contact: Anna Smith, Tel.: (510)486-7493. E-mail: [email protected]

Web: http://qm2004.lbl.gov/

January 25–February 1

Bormio, Italy. XLII International

Winter Meeting on Nuclear Physics.

Contact: I. Iori or A. Moroni, [email protected] or [email protected]

Web: http://www.mi.infn.it/bormio

March 2–12

ECT*, Trento, Italy. Spectroscopic

Factors. Contact: Angela Bonaccorso,[email protected]

Web: http://www.df.unipi.it/~angela/Trento04.html

March 24–27

Grenoble, France. INSTAR2004:

Workshop on the Physics of Excited

Baryons. Contact: [email protected]: http://lpsc.in2p3.fr/congres/

nstar2004

April 5–7

Gaithersburg, MD, USA. Inter-

national Conference on Precision

Measurements with Slow Neutrons.

Contact: Local Organizing Committee,[email protected]

Web: h t tp : / /phys ics .n i s t .gov/Div is ions /Div846/S lowNeutrons/index.html

calendar

April 19–22

Hacienda Cocoyoc, Morelos,

México. Nuclear Physics, Large and

Small: Microscopic Studies of

Collective Phenomena. Contact: Dr.Roelof Bijker, [email protected]

Web: http://www.nuclecu.unam.mx/~bijker/StuFiesta.html

May 23–27

Paestum, Italy. 8th International

Spring Seminar on Nuclear Physics:

Key Topics in Nuclear Structure.

Web: http://www.na.infn.it/paestum2004

May 23–28

Indiana University, Bloomington,

IN, USA. QNP2004 Conference.

Web: http://www.qnp2004.org

May 24–28

ECT*, Trento, Italy. Workshop on

“Advances and Challenges in Nuclear

Astrophysics.” Contact: CarmenAngulo, Coordinator (CRC Louvain-la-Neuve): [email protected]. be

Web: http://www.ect.it/html/projects/2004/wks/Welcome.html

June 8–11

Grenoble, France. From Parity

Violation to Hadronic Structure and

More . . . Part II. Contact: Serge Kox,[email protected]

Web: http:/ / lpscwww.in2p3.fr /congres/pavi2004/index.html

June 20–25

University of Surrey, Guildford,

UK. Modern Trends in Activation

Analysis. Contact: Prof. N. Spyrou,[email protected]

Web: http://www.mtaa11.com

June 27–July 2

Göteborg, Sweden. International

Nuclear Physics Conference,

INPC 2004. Contact: [email protected]

Web: http://www.fy.chalmers.se/INPC2004

July 5–12

Peterhof, Russia. International

Symposium on Exotic Nuclei

(EXON-2004). Contact: [email protected]

Web: http://www.jinr.ru/exon2004/

July 19–23

Vancouver, BC, Canada. The 8th

International Symposium on Nuclei in

the Cosmos, NIC VIII. Contact:[email protected]

Web: http://www.triumf.ca/nic8

July 26–30

Argonne National Laboratory,

Argonne, IL, USA. Conference on

“Nuclei at the Limits.” Contact:Jeannie Glover, [email protected]

Web: h t tp : / /www.phy.an l . govlimits04

September 12–16

Callaway Gardens Resort, Pine

Mountain, GA, USA. The Fourth Inter-

national Conference on Exotic Nuclei

and Atomic Masses (ENAM’04).

Contact: [email protected]: http://www.phy.ornl.gov/

enam04/

December 15–16

Université Libre de Bruxelles,

Brussels, Belgium. 20th Brussels

meeting between astrophysicists and

nuclear physicists. Contact: [email protected] or [email protected]

Web: ht tp : / /pntpm3.ulb .ac .be/brussels2003

2005January 5–8

University of Surrey, Guildford,

UK. The International Conference

on Nuclear Structure, Astrophysics

and Reactions (NUSTAR’05).

Contact: Paddy Regan, Chair,[email protected]

Documents

NPN 13(4) Inside - NuPECCswitchyard toward the accelerator. editorial Vol. 13, No. 4, 2003, Nuclear Physics News 3 Precarious Careers, Uncertain Futures I graduated with a degree in