3He Neutron Detection Alternatives for Radiation Portal Monitors

Richard KouzesKen Conlin, James Ely, Luke Erikson, Azaree Lintereur, Emily Mace, Edward Siciliano, Daniel Stephens, David Stromswold, Renee Van

Ginhoven, Mitch WoodringPacific Northwest National Laboratory

Work Supported by DOE, DOD, DHS, PNNL

IAEA 3He WorkshopMarch 22-24, 2011

PNNL-SA-77910

2

The 3He Problem

National security and science applications have driven up demand for 3He for neutron detection

Currently, 3He comes solely from the processing of tritium

No significant production of new tritium Production of tritium solely for 3He need is cost

prohibitive Reserves of 3He have been consumed Projected 3He Supply ~10-20 kL/y (U.S.& Russia) Demand for 3He was ~65 kL/y – now reduced Nothing matches all of the capabilities of 3He An alternative is needed now

2 3He Tubes

3He Applications 3He is a rare isotope with important uses in:

Neutron detection

science

national security

safeguards

oil/gas exploration

Industrial applications

Low-temperature physics

Lung imaging

Missile guidance

Laser research

Fusion3

3He Characteristics

3He is excellent for neutron detection Large thermal neutron capture cross-section Inert gas Good gamma ray rejection

4

3He Demand Forecast: FY09

5

Data From Steve Fetter, OSTP

Supply

Projected demand ~65 kL/y - Projected Supply ~10-20 kL/y

3He Demand Forecast: FY1

6

Plot From Julie Bentz, National Security Staff

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Border Security Examples

Over 1400 RPM systems deployed in US

About 3000 RPM systems deployed worldwide

Neutron and gamma ray detection

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Alarms and “Nuisance” Alarms

Few sources of Neutron Alarms (~1/10,000) Troxler gauges, well logging sources, nuclear fuel,

yellowcake Nuisance alarms: large gamma ray sources and “ship effect”

Gamma Ray Nuisance Alarms (~1/100) agricultural products like fertilizer kitty litter ceramic glazed materials aircraft parts and counter weights propane tanks road salt welding rods ore and rock smoke detectors camera lenses televisions medical radioisotopes

Troxler Gauge

Requirements for Neutron Detection for National Security

Plutonium emits detectable quantities of neutrons Neutron background arises from cosmic ray produced

secondaries and is a very low rate (~1000 times smaller than gamma ray background)

Neutron alarms initiate a special Operating Procedure

Fast and slow neutron detection required with flat response Absolute efficiency per panel: єabs = 0.11% or 2.5 cps/ng 252Cf Gamma ray discrimination of better than 10-6

Maintain neutron detection efficiency in presence of gamma rays: gamma absolute rejection ratio (0.9 < GARRn < 1.1)

Meet all ANSI N42.35/N42.38 requirements

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Requirements for Alternative Neutron Detection for National Security

Physically fit in the volume currently occupied by the neutron detection assembly in existing systems

Electronics compatible with existing system Thermal and fast neutron detection Non-responsive to gamma rays Rugged, reliable, and accurate Safe Inexpensive Readily available commercially now

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Alternative Neutron Detectors Proportional Counter Alternatives

BF3 filled proportional counters Boron-lined proportional counters

Scintillator-based Alternatives Coated wavelength shifting fibers/paddles Scintillating glass fibers loaded with 6Li Crystalline: LiI(Eu), LiF(W), Li3La2(BO3)3(Cr) Liquid scintillator

Semiconductor Neutron Detectors in Development Gallium arsenide, perforated semiconductor, boron carbide,

boron nitride, pillar-structured detectors High efficiency, but limited in size

Other: doped glasses, Li-foil ion chamber, Li phosphate nanoparticles, fast neutron detectors

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Existing Commercial Alternative Neutron Detectors

Proportional Counter Alternatives BF3 filled proportional counters

Boron-lined proportional counters

Scintillator-based Alternatives Plastic fiber/paddle light-guides coated with

ZnS scintillator and 6Li neutron absorber Scintillating glass fibers loaded with 6Li

Systems from 9 vendors tested

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Boron-based Detectors

“Straw tube” designs (Proportional Technology)

Multi-chamber boron lined approachesLND Centronic

BF3 (LND)

Boron lined (Reuter Stokes)

BF3 Proportional Counters

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Neutrons captured by the 10B (>90%) yields α + 7Li Gas pressure must be low (0.5 to 1.0 atm.) to operate

at reasonable voltages (2000-2500 V) Cross-section ~70% that of 3He Advantages

Inexpensive direct replacement for 3He Better gamma-neutron separation than 3He

Disadvantages BF3 is toxic, difficult to purify, degrades over time, and is

corrosive to the gas enclosure Subject to strict DOT shipping regulations Requires the use of multiple tubes to meet capability Requires changes to electronics

Boron-Lined Proportional Counters

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Similar detection mechanism to BF3 (yields α + 7Li) Boron in matrix on walls; more signal amplitude spread Advantages

New prototypes promise needed efficiency Better gamma-neutron separation than 3He Direct tube replacement for 3He Only minor electronics changes

Disadvantages Counting efficiency is lower than that of either 3He or BF3

More variation in pulse height Requires the use of multiple tube assembly to meet

efficiency requirement

ZnS + 6Li-coated Light-guide Detectors Paddles or fibers coated with ZnS

scintillator mixed with 6Li Advantage

Comparable performance to 3He tube(s) Disadvantages

Gamma-ray discrimination as tested required improvement for fiber version

Possible significant change to electronics

Coated Paddles(Symetrica)

Coated Fibers (IAT) Coated Paddles (SAIC)

6Li Loaded Glass Fibers

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6Li-enriched lithium silicate glass fibers doped with cerium (Bliss et al. 1995, PNNL)

Neutron capture on 6Li produces charged particles that cause Ce ions to fluoresce (observed by photomultiplier tubes)

Advantages Comparable performance to one 3He tube Fibers can be formed into different shapes

Disadvantages Less gamma-ray discrimination than 3He Possible significant change to electronics

PNNL Neutron Detector Testing Measurements of neutron efficiency have been carried

out at PNNL for standard deployable RPM systems. Testing of alternatives:

3He at pressures of 1.0, 2.0, 2.5 and 3 atmospheres BF3 filled proportional counter tubes Boron-lined proportional counters ZnS-6Li coated plastic fibers/paddles Glass fibers loaded with 6Li

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Detection efficiency (cps/ng) for shielded source Uncertainty primarily due to uncertainty in source activity

0

0.5

1

1.5

2

2.5

3

3.5

He-3

(SAIC

)

He-3

(ext

erna

l)

BF3 (1

tube)

BF3 (2

tube)

BF3 (3

tube)

BF3 (4

tube)

De

tec

tor

Eff

icie

nc

y (

cp

s/n

g)

ASP spec

RPM spec

ANSI N42.35

BF3 Results

Modeled with MCNPGood qualitative agreement with data

Boron-lined Neutron Detection

0.0E+00

2.0E-07

4.0E-07

6.0E-07

8.0E-07

1.0E-06

1.2E-06

1.4E-06

1.6E-06

1.8E-06

2.0E-06

0.05 0.25 0.45 0.65 0.85 1.05 1.25 1.45 1.65 1.85

Co

un

ts p

er

em

itte

d n

eru

tro

n p

er

10

ke

V

Energy Bins (MeV)

Alpha & Li Currents from B-lined Tube w/ 252Cf in Pig 2m from RSP

Alpha Current Into Gas

Li7 Current Into Gas

Total Current Into Gas

Insensitive to 60Co gamma rays (~10-8)Good neutron efficiency with gamma ray discriminating

threshold

Boron-Lined Gamma Discrimination

Neutron and gamma pulse from IAT system Differences in pulse shape allow for pulse-shape

discrimination

Neutron Pulse Gamma Pulse

ZnS + 6Li-coated Fiber Signal

All options will require hardware and software modifications

Summary of Technology Testing

Technology Efficiency Gamma Rejection

Voltage Comments

3He       Gold standard

BF3       Hazardous gasHigh operating voltage

Boron-lined       Meets requirements

Coated Plastic Paddles

      Meets requirements

Coated Plastic Fiber

      As tested, efficiency requirement not quite met

Glass Fiber       Issues with neutron and gamma ray efficiency Only small version tested.

Does Not Meet Requirement

Meets Requirement

Conclusions

Applications for 3He are diverse

Demand is greater than supply

The national security need for an alternative is immediate

Four alternative neutron detection technologies have been tested

Alternatives for RPM systems can meet the technical requirements for national security applications

Support

Work supported by: DOE NNSA DoD DHS DNDO PNNL

Thank you!

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Backup

3He Supply

3He not currently extracted from natural supplies Primordial abundance of 3He:4He is 1:100001.4 ppm by volume atmospheric He 0.2 ppm by volume natural-gas He (fission product)Lunar sources

By-product of nuclear weapons programTritium was produced for nuclear weapons in reactorsTritium production in U.S. ended in 1988 since weapon needs met through reductions in weapon stockpile, recycleTritium production restarted in U.S. in 2007 only to support smaller stockpileTritium decays with 12.4-year half-life to to 3HeSeparated 3He made available by DOE SC/NP Isotope ProgramU.S. accumulated 200,000 liters of 3He by the end of 1990s Decay produces ~8000 liters/year of 3He in U.S.

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Estimate of Supply and Demand

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Data from Steve Fetter, OSTP

3He Five Year Usage: All Applications

Data from Linde Electronics and Specialty GasesFrom Ron Cooper, ORNL

3He Demand – AAAS Study

Neutron Scattering: 120,000 liters over the next five yearsHomeland Security:

Historically large1000 – 2000 liters / year for 5 yearsDropping to zero once alternative technologies become available

Medical Imaging: 2000 liters / yearCryogenics: 2500 – 3000 liters / yearOil and gas exploration: 2000 liters / yearDOE “emergency response assets”: few 1000 liters / yearOther fields: each require a few hundred liters / year

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Type GRR GARRn ε Detail3He BT 10-8 1.0 3.13 Single 3 atm tube

BF3 BT 10-8 NM 1.6 Single tube, 3 tubes = 3.0

Boron-lined PC BT 10-8 NM 0.16 Single tube, 3 tubes = 0.25

Boron-lined MTPC BT 10-7 1.01 3.01 Full volume

Boron-lined MTPC BT 10-8 1.01 0.98 Single tube

Boron-lined MTPC BT 10-8 1.06 0.12 12” tube, scaled to 3 tubes =~1.5

Straw tubes (B-lined) BT 10-8 1.0 4.0 Full volume

Coated Plastic Fiber 10-8 1.03 2.0 ~ Full volume

Coated Plastic Paddle BT 10-7 1.01 0.9 Small system, scaled by 4x =~3.5

Lithium Glass Fiber 10-7 1.31 0.32 Middle setting (0.18*volume)

Comparative Results

GRR = Gamma Ray Rejection

GARRn = Gamma Absolute Rejection Ratio

BT = Better Than

PC = proportional counter

MTPC = multi-tube (or multi-chamber) proportional counter