Vg# 1 June 12, 2009 Mark Grohman Mark Derzon Ronald Renzi Eduardo Padilla Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed.

Vg# 1

June 12, 2009June 12, 2009Mark GrohmanMark Grohman

Mark DerzonMark DerzonRonald RenziRonald Renzi

Eduardo PadillaEduardo 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.

Micro Capillary Micro Capillary Technology for Technology for Fast Neutron Fast Neutron Detection and Detection and

ImagingImaging

Vg# 2

The Detection Problem

Passive Detection Example at a portal

Vg# 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

Vg# 4

Active Interrogation Concept

The interrogation source is being developed.

Mobile Dual Neutron/Gamma Interrogation System

But what exactly are these detector arrays?

Vg# 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?

Vg# 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

Vg# 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

Vg# 8

Helium Neutron Detector Concept

• 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

Readout / Electronics

Gas Reservoir

Neutrons

High PressureCapillary Array

Scintillation lightor Ionization Current

• 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

Vg# 9

2008 Tests of Individual Capillaries using Electrical Readout

Conceptual proof of thermal neutron detector concept

Vg# 10

MeV Neutron Energy Deposition

10-2

10-1

100

101

10-1 100 101

Ave

rag

e E

ner

gy

Dep

osi

ted

Per

Co

llis

ion

(M

eV)

Neutron Energy (MeV)H1_He3_He4_EnergyPerCol.qpc

Plastic Scintillator

Helium 4

Helium 3

14 MeV2.5 MeV

50% larger

Vg# 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

Vg# 12

High-Pressure natural helium neutron detector concept at 1400 bar

• Design based from HIP standardreactor

• Devices will attach to a bracket that attaches to the plug

• Internal dimensions are1.5” diameter & 1.3” tall

• Certified @ 20 KSI MAWP

Neutron source

1.5 KV feeds (25 ksi rated)

High pressurecone and thread

ports

Seal area (details not shown)

Approx. size is 4.5” dia. & 6” long

Renzi 11/08

Vessel plug

Long ‘thin’Channels

Vg# 13

MCNPX Modeling of Simplified Pressure Vessel and He DetectorSS Pressure

Vessel ABS Plastic Spacer Active Detector

Element

Vg# 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

Vg# 15

Neutron Energy Spectrum in Each He Capillary

Vg# 16

He Energy Deposition Spectrum in Each He Capillary

Vg# 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

Vg# 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

Vg# 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

Vg# 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