June 12, 2009 Mark Grohman Mark Derzon Ronald Renzi Eduardo Padilla

1. Micro Capillary Technology for Fast Neutron Detection and Imaging June 12, 2009 Mark Grohman Mark Derzon Ronald Renzi Eduardo Padilla Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company,for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

2. The Detection Problem Passive Detection Example at a portal

3. Issues with Passive Detection • Low signals from Special Nuclear Material • Shielding always present to some degree • Keep the trucks moving, but higher speed means reduction in detection ability • Naturally Occurring Nuclear Materials (NORM) frequently are present, obscuring the SNM signal • Increasing detector size increases background interferents as well as signal Solution: Increase target signal without a corresponding increase in background

4. Mobile Dual Neutron/Gamma Interrogation System But what exactly are these detector arrays? Active Interrogation Concept The interrogation source is being developed.

5. Detector Issues • Detector saturation when interrogation source is on • Fast recovery necessary from 10 orders of magnitude in source signal versus target signal • Need large detectors for measuring small target signal • Detector electronics must withstand harsh environment near the AI accelerator hardware Bottom line: How can existing detectors handle this harsh situation?

6. Detector Approaches • Existing Detectors for AI concepts are always off when beam is on • Prompt neutron and gamma signals therefore cannot be measured • Existing concepts use the delayed response over a long time • However, the prompt signal is 2-3 orders of magnitude higher than the delayed signal Future: The community needs detectors which can measure prompt and delayed signals

7. Divide and Conquer • Increase Signal to Noise By Detector Design • Reduce the detector scale by n pixels • Background will be reduced by n • But the signal per pixel is unchanged • Higher pressure and specific signal • Increase rate limits by segmentation; reduce long-time tail on pulses • Radiation hardened processing electronics and sensors required • High aspect ratio provides directionality • Reduce average Z – reduce the gamma background • Three things come to mind • Micro-machining • Micro-fluidics • Micro-electronics

8. Helium Neutron Detector Concept Scintillation light or Ionization Current High Pressure Capillary Array Gas Reservoir • This detector system utilizes neutron reactions with high-pressure Helium gas to generate detectable scintillation photons or charged particles • Sandia’s MEMs and fluidics technologies allows for extremely high pressure fluid and gas fills of capillary arrays, ~2000 bar, yielding enhanced detection efficiency with the greater gas density Neutrons Readout / Electronics • A compact pixilated detector results which is naturally compatible with neutron imaging as well as neutron spectroscopy • This detector has a high neutron to gamma detection sensitivity due to the high neutron cross-sections, low Z Helium gas fill, favorable ion to electron scintillation efficiency and long electron deposition range

9. 2008 Tests of Individual Capillaries using Electrical Readout Conceptual proof of thermal neutron detector concept

10. MeV Neutron Energy Deposition 50% larger Helium 3 Helium 4 Plastic Scintillator 2.5 MeV 14 MeV

11. Sensor Fill material • Hydrogen is best for neutron scattering • Explosive hazard • Corrosive material • Insufficient electrons to stop ionized nucleus • Helium-3 is next best • Tritium contamination • Non-corrosive • Labeled Special Nuclear Material (SNM) • Supply limited and expensive • Stopping gas needed up to about 2500 bar • Helium-4 was chosen • Non-corrosive • No stopping gas needed at 1400 bar • Plentiful and inexpensive

12. High-Pressure natural helium neutron detector concept at 1400 bar

13. MCNPX Modeling of Simplified Pressure Vessel and He Detector SS Pressure Vessel ABS Plastic Spacer Active Detector Element

14. MCNPX Modeling of Simplified He Detector • 1.4” diameter of ABS Spacer and active detector element • Active detector element consists of .002” Cu plating on both sides, of the .020” FR4* PCB, with 10 .024” electrode gaps • Interior cavity of the SS pressure vessel is filled with 20kPSI He gas Alternating cells of FR4*, He Gas and Cu electrodes

15. Neutron Energy Spectrum in Each He Capillary

16. He Energy Deposition Spectrum in Each He Capillary

17. Proof-of-Principle Fast Neutron Device • Layered approach with stacked sensor elements • Pressure not contained in sensor element as yet • Electronics not yet integrated into each individual element • Low flux design • Housed in pressure vessel • Including carrying case, the weight estimated at less than 20 kg • A compact pixilated detector which is naturally compatible with neutron imaging as well as neutron spectroscopy

18. Summary of Benefits • MEMs and fluidics technologies allows for extremely high pressure fluid and gas fills of capillary arrays, >1000 bar will yield high efficiency • Modeling suggests improvements by a factor of many over traditional plastic scintillators: • number of signal carriers • Signal-to-Noise improvements for certain imaging applications • Reduction in the sensitivity to bremsstrahlung radiation • Spatial resolution enhancements • Data rate can be extremely high • A high neutron to gamma detection sensitivity due to low Z helium gas fill and long electron deposition range

19. Plans • Hardware finishing in June 2009 • Accelerator testing July-August • Update model in September • Demonstrate angular discrimination in October • Measure gamma/neutron rejection ratio with Pulse Shape Discrimination in December • Finalize neutron detection model in January 2010 • Future work to be proposed: • Pressurize capillaries outside of pressure vessel • Convert to silicon wafer and integrate analog electronics

20. Acknowledgements Gordon Chandler, Dora Derzon, Dave Zanini, Jim Van DeVruege, Dan Yee, Ted Parson, Shawn Martin, Larry Sanchez, Kevin Seager, Dusty Rhoades, Joseph Graham, Phil Bennett, Jerry Inman, and Cindy Alvine