1. 3 He Neutron Detection Alternatives for Radiation Portal Monitors 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 Work Supported by DOE, DOD, DHS, PNNL IAEA 3 He Workshop March 22-24, 2011 PNNL-SA-77910

2. 2 The 3 He Problem  National security and science applications have driven up demand for 3 He for neutron detection  Currently, 3 He comes solely from the processing of tritium  No significant production of new tritium  Production of tritium solely for 3 He need is cost prohibitive  Reserves of 3 He have been consumed  Projected 3 He Supply ~10-20 kL/y (U.S.& Russia)  Demand for 3 He was ~65 kL/y – now reduced  Nothing matches all of the capabilities of 3 He  An alternative is needed now 2 3 He Tubes

3. 3 He Applications  3 He 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 Fusion 3

4. 3 He Characteristics  3 He is excellent for neutron detection  Large thermal neutron capture cross-section  Inert gas  Good gamma ray rejection 4

5. 3 He Demand Forecast: FY09 5 Data From Steve Fetter, OSTP Supply Projected demand ~65 kL/y - Projected Supply ~10-20 kL/y

6. 3 He Demand Forecast: FY1 6 Plot From Julie Bentz, National Security Staff

7. 7 Border Security Examples  Over 1400 RPM systems deployed in US  About 3000 RPM systems deployed worldwide  Neutron and gamma ray detection

8. 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

9. 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: є abs = 0.11% or 2.5 cps/ng 252 Cf  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

10. 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

11. Alternative Neutron Detectors  Proportional Counter Alternatives  BF 3 filled proportional counters  Boron-lined proportional counters  Scintillator-based Alternatives  Coated wavelength shifting fibers/paddles  Scintillating glass fibers loaded with 6 Li  Crystalline: LiI(Eu), LiF(W), Li 3 La 2 (BO 3 ) 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

12. Existing Commercial Alternative Neutron Detectors  Proportional Counter Alternatives  BF 3 filled proportional counters  Boron-lined proportional counters  Scintillator-based Alternatives  Plastic fiber/paddle light-guides coated with ZnS scintillator and 6 Li neutron absorber  Scintillating glass fibers loaded with 6 Li  Systems from 9 vendors tested 12

13. Boron-based Detectors “Straw tube” designs (Proportional Technology) Multi-chamber boron lined approaches LND Centronic BF 3 (LND) Boron lined (Reuter Stokes)

14. BF 3 Proportional Counters 14  Neutrons captured by the 10 B (>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 3 He  Advantages  Inexpensive direct replacement for 3 He  Better gamma-neutron separation than 3 He  Disadvantages  BF 3 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

15. Boron-Lined Proportional Counters 15  Similar detection mechanism to BF 3 (yields α + 7 Li)  Boron in matrix on walls; more signal amplitude spread  Advantages  New prototypes promise needed efficiency  Better gamma-neutron separation than 3 He  Direct tube replacement for 3 He  Only minor electronics changes  Disadvantages  Counting efficiency is lower than that of either 3 He or BF 3  More variation in pulse height  Requires the use of multiple tube assembly to meet efficiency requirement

16. ZnS + 6 Li-coated Light-guide Detectors  Paddles or fibers coated with ZnS scintillator mixed with 6 Li  Advantage  Comparable performance to 3 He 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)

17. 6 Li Loaded Glass Fibers 17  6 Li-enriched lithium silicate glass fibers doped with cerium (Bliss et al. 1995, PNNL)  Neutron capture on 6 Li produces charged particles that cause Ce ions to fluoresce (observed by photomultiplier tubes)  Advantages  Comparable performance to one 3 He tube  Fibers can be formed into different shapes  Disadvantages  Less gamma-ray discrimination than 3 He  Possible significant change to electronics

18. PNNL Neutron Detector Testing  Measurements of neutron efficiency have been carried out at PNNL for standard deployable RPM systems.  Testing of alternatives:  3 He at pressures of 1.0, 2.0, 2.5 and 3 atmospheres  BF 3 filled proportional counter tubes  Boron-lined proportional counters  ZnS- 6 Li coated plastic fibers/paddles  Glass fibers loaded with 6 Li 18

19.  Detection efficiency (cps/ng) for shielded source  Uncertainty primarily due to uncertainty in source activity ASP spec RPM spec ANSI N42.35 BF 3 Results

20.  Modeled with MCNP  Good qualitative agreement with data Boron-lined Neutron Detection

21.  Insensitive to 60 Co gamma rays (~10 -8 )  Good neutron efficiency with gamma ray discriminating threshold Boron-Lined Gamma Discrimination

22.  Neutron and gamma pulse from IAT system  Differences in pulse shape allow for pulse-shape discrimination Neutron PulseGamma Pulse ZnS + 6Li-coated Fiber Signal

23. All options will require hardware and software modifications Summary of Technology Testing TechnologyEfficiencyGamma Rejection VoltageComments 3 He Gold standard BF 3 Hazardous gas High 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

24. Conclusions  Applications for 3 He 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

25. Support  Work supported by:  DOE NNSA  DoD  DHS DNDO  PNNL Thank you!

26. 26 Backup

27. 3 He Supply 3 He not currently extracted from natural supplies Primordial abundance of 3 He: 4 He is 1:10000 1.4 ppm by volume atmospheric He 0.2 ppm by volume natural-gas He (fission product) Lunar sources By-product of nuclear weapons program Tritium was produced for nuclear weapons in reactors Tritium production in U.S. ended in 1988 since weapon needs met through reductions in weapon stockpile, recycle Tritium production restarted in U.S. in 2007 only to support smaller stockpile Tritium decays with 12.4-year half-life to to 3 He Separated 3 He made available by DOE SC/NP Isotope Program U.S. accumulated 200,000 liters of 3 He by the end of 1990s Decay produces ~8000 liters/year of 3 He in U.S. 27

28. Estimate of Supply and Demand 28 Data from Steve Fetter, OSTP

29. 3 He Five Year Usage: All Applications Data from Linde Electronics and Specialty Gases From Ron Cooper, ORNL

30. 3 He Demand – AAAS Study Neutron Scattering: 120,000 liters over the next five years Homeland Security: Historically large 1000 – 2000 liters / year for 5 years Dropping to zero once alternative technologies become available Medical Imaging: 2000 liters / year Cryogenics: 2500 – 3000 liters / year Oil and gas exploration: 2000 liters / year DOE “emergency response assets”: few 1000 liters / year Other fields: each require a few hundred liters / year 30

31. TypeGRRGARRnεDetail 3 HeBT 10 -8 1.03.13 Single 3 atm tube BF 3 BT 10 -8 NM1.6 Single tube, 3 tubes = 3.0 Boron-lined PCBT 10 -8 NM0.16 Single tube, 3 tubes = 0.25 Boron-lined MTPCBT 10 -7 1.013.01 Full volume Boron-lined MTPCBT 10 -8 1.010.98 Single tube Boron-lined MTPCBT 10 -8 1.060.12 12” tube, scaled to 3 tubes =~1.5 Straw tubes (B-lined)BT 10 -8 1.04.0 Full volume Coated Plastic Fiber10 -8 1.032.0 ~ Full volume Coated Plastic PaddleBT 10 -7 1.010.9 Small system, scaled by 4x =~3.5 Lithium Glass Fiber10 -7 1.310.32 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