Richard Kouzes Ken Conlin James Ely Luke Erikson Azaree Lintereur Emily Mace Edward Siciliano Daniel Stephens David Stromswold Renee Van Ginhoven Mitch Woodring Pacific Northwest National Laboratory ID: 332337
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Slide1
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 LaboratoryWork Supported by DOE, DOD, DHS, PNNLIAEA 3He WorkshopMarch 22-24, 2011
PNNL-SA
-77910Slide2
2
The 3He ProblemNational security and science applications have driven up demand for 3He for neutron detection
Currently,
3
He comes solely from the processing of tritium
No significant production of new tritiumProduction of tritium solely for 3He need is cost prohibitiveReserves of 3He have been consumedProjected 3He Supply ~10-20 kL/y (U.S.& Russia)Demand for 3He was ~65 kL/y – now reducedNothing matches all of the capabilities of 3HeAn alternative is needed now
2
3
He TubesSlide3
3He Applications
3He is a rare isotope with important uses in:Neutron detection sciencenational securitysafeguards oil/gas explorationIndustrial applicationsLow-temperature physicsLung imagingMissile guidance Laser research
Fusion
3
Slide4
3He Characteristics
3He is excellent for neutron detectionLarge thermal neutron capture cross-sectionInert gasGood gamma ray rejection4 Slide5
3He Demand Forecast: FY09
5 Data From Steve Fetter, OSTP
Supply
Projected demand ~65 kL/
y
- Projected Supply ~10-20 kL/ySlide6
3He Demand Forecast: FY1
6 Plot From Julie Bentz, National Security Staff Slide7
7
Border Security ExamplesOver 1400 RPM systems deployed in USAbout 3000 RPM systems deployed worldwideNeutron and gamma ray detectionSlide8
8
Alarms and “Nuisance” AlarmsFew 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 litterceramic glazed materials aircraft parts and counter weightspropane tanksroad saltwelding rodsore and rocksmoke detectorscamera lensestelevisionsmedical radioisotopesTroxler GaugeSlide9
Requirements for Neutron Detection for National Security
Plutonium emits detectable quantities of neutronsNeutron 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 ProcedureFast and slow neutron detection required with flat response
Absolute efficiency per panel:
є
abs
= 0.11% or 2.5 cps/ng 252CfGamma ray discrimination of better than 10-6Maintain neutron detection efficiency in presence of gamma rays: gamma absolute rejection ratio (0.9 < GARRn < 1.1)Meet all ANSI N42.35/N42.38 requirements9 Slide10
Requirements for Alternative
Neutron Detection for National SecurityPhysically fit in the volume currently occupied by the neutron detection assembly in existing systemsElectronics compatible with existing systemThermal and fast neutron detectionNon-responsive to gamma rays
Rugged, reliable, and accurate
Safe
Inexpensive
Readily available commercially now10 Slide11
Alternative Neutron Detectors
Proportional Counter AlternativesBF3 filled proportional countersBoron-lined proportional countersScintillator-based AlternativesCoated wavelength shifting fibers/paddles
Scintillating glass fibers loaded with
6
Li
Crystalline: LiI(Eu), LiF(W), Li3La2(BO3)3(Cr)Liquid scintillatorSemiconductor Neutron Detectors in DevelopmentGallium arsenide, perforated semiconductor, boron carbide, boron nitride, pillar-structured detectorsHigh efficiency, but limited in sizeOther: doped glasses, Li-foil ion chamber, Li phosphate nanoparticles, fast neutron detectors11 Slide12
Existing Commercial
Alternative Neutron DetectorsProportional Counter AlternativesBF3 filled proportional countersBoron-lined proportional countersScintillator-based Alternatives
Plastic fiber/paddle light-guides coated with ZnS scintillator and
6
Li neutron absorber
Scintillating glass fibers loaded with 6LiSystems from 9 vendors tested12 Slide13
Boron-based Detectors
“Straw tube” designs (Proportional Technology)Multi-chamber boron lined approachesLND Centronic
BF
3
(LND)
Boron lined (Reuter Stokes)Slide14
BF
3 Proportional Counters14 Neutrons captured by the 10B (>90%) yields α
+
7
Li
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 AdvantagesInexpensive direct replacement for 3HeBetter gamma-neutron separation than 3HeDisadvantages BF3 is toxic, difficult to purify, degrades over time, and is corrosive to the gas enclosure Subject to strict DOT shipping regulationsRequires the use of multiple tubes to meet capabilityRequires changes to electronicsSlide15
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 efficiencyBetter gamma-neutron separation than 3HeDirect tube replacement for 3HeOnly minor electronics changesDisadvantages Counting efficiency is lower than that of either 3He or BF3More variation in pulse height
R
equires
the use of multiple tube
assembly
to meet efficiency requirementSlide16
ZnS + 6
Li-coated Light-guide Detectors
Paddles or fibers coated with ZnS scintillator mixed with
6
Li
AdvantageComparable performance to 3He tube(s)DisadvantagesGamma-ray discrimination as tested required improvement for fiber versionPossible significant change to electronics Coated Paddles(Symetrica)
Coated Fibers (IAT)
Coated Paddles (SAIC)Slide17
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
3
He tubeFibers can be formed into different shapesDisadvantagesLess gamma-ray discrimination than 3HePossible significant change to electronics Slide18
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 BF
3
filled proportional counter tubes
Boron-lined proportional counters
ZnS-6Li coated plastic fibers/paddles Glass fibers loaded with 6Li18 Slide19
Detection efficiency
(cps/ng) for shielded source Uncertainty primarily due to uncertainty in source activity
ASP spec
RPM spec
ANSI N42.35
BF3 ResultsSlide20
Modeled with MCNP
Good qualitative agreement with dataBoron-lined Neutron DetectionSlide21
Insensitive to
60Co gamma rays (~10-8)Good neutron efficiency with gamma ray discriminating thresholdBoron-Lined
Gamma DiscriminationSlide22
Neutron
and gamma pulse from IAT systemDifferences in pulse shape allow for pulse-shape discrimination
Neutron Pulse
Gamma Pulse
ZnS + 6Li-coated Fiber SignalSlide23
All options will require hardware and software modifications
Summary of Technology TestingTechnologyEfficiency
Gamma Rejection
Voltage
Comments
3He Gold standard
BF
3
Hazardous
gas
H
igh
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 RequirementSlide24
Conclusions
Applications for 3He are diverse Demand is greater than supplyThe national security need for an alternative is immediateFour alternative neutron detection technologies have been testedAlternatives for RPM systems can meet the technical requirements for national security applicationsSlide25
Support
Work supported by:DOE NNSADoDDHS DNDO PNNLThank you!Slide26
26
BackupSlide27
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 sourcesBy-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
3
He by the end of 1990s
Decay produces ~8000 liters/year of
3He in U.S.27 Slide28
Estimate of Supply and Demand
28 Data from Steve Fetter, OSTPSlide29
3
He Five Year Usage: All ApplicationsData from Linde Electronics and Specialty GasesFrom Ron Cooper, ORNL Slide30
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 availableMedical 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 / year30 Slide31
Type
GRRGARRn
ε
Detail
3
HeBT 10-81.03.13Single 3 atm tube
BF
3
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