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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
7
Border Security Examples
Over 1400 RPM systems deployed in US
About 3000 RPM systems deployed worldwide
Neutron and gamma ray detection
8
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
9
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
10
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
11
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
12
Boron-based Detectors
“Straw tube” designs (Proportional Technology)
Multi-chamber boron lined approachesLND Centronic
BF3 (LND)
Boron lined (Reuter Stokes)
BF3 Proportional Counters
14
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
15
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
17
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
18
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!
26
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.
27
Estimate of Supply and Demand
28
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
30
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