The goals of this project are: (1) detect and locate a source of thermal neutrons; (2) distinguish a localized source from uniform background; (3) show shape and size of thermalizing material; (4) test thermal neutron imager in active interrogation environment; and (5) distinguish delayed neutrons from prompt neutrons

Vanier, P. E.

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Office of Nonproliferation Research and DevelopmentSNM Movement Detection / Radiation Sensors and Advanced Materials Portfolio ReviewThermal neutron imaging support with other laboratories   BL06-IM-TNIJune 17-19, 2008Peter E. VanierBrookhaven National LaboratoryJune 17, 20082Thermal neutron imaging support with other laboratoriesPrincipal Investigator: Peter VanierSub-Contractor: Leon Forman, Ion Focus TechnologyCo-investigators: Graham Smith Cynthia SalwenNeil Schaknowski Istvan DioszegiJoe Mead Lisa RamirezVinita GhoshCollaborators: James Jones, INLDaren Norman, INLGus Caffrey, INLKlaus Ziock, LLNL and ORNLTim Brown, SRNLBudget: 2006 2007 2008$150k $150k $150k3Project overviewGoals:Detect and locate a source of thermal neutronsDistinguish a localized source from uniform backgroundShow shape and size of thermalizing materialTest thermal neutron imager in active interrogation environmentDistinguish delayed neutrons from prompt neutrons4Technical approach• Compressed He-3 position-sensitive wire chamber• Cadmium coded aperture• Continuous acquisition for passive mode• Time-gated data acquisition for active mode • Fast Fourier Transform processing5Early papers on coded apertures• E.E. Fenimore and T.M. Cannon, “ Coded Aperture Imaging with Uniformly Redundant Arrays, ” Applied Optics, 17, 337-347, (1978)• E.E. Fenimore and T.M. Cannon, “Uniformly Redundant Arrays: digital reconstruction methods”, Applied Optics, 20, 1858-64 (1981)• S.R. Gottesman and E.E. Fenimore, “New family of binary arrays for coded aperture imaging”, Applied Optics, 28, 4344-52, (1989)6Thermal neutron imaging support with other laboratoriesDeliverables:• Quarterly Technical Reports• Quarterly Budget Reports• Publications• Presentations at Conferences • Final Technical ReportCapability improvement addressed by project success (relevant to the non-proliferation mission):• Improved search capability• Improved diagnostic capability• Improved arms control signatures• Improved active interrogation of shipping containers• Improved explosives detection capability• Improved monitoring of dry fuel storage containers7Progress to date Various neutron sources•Cf-252 (spontaneous fission)•Am-241+Li (alpha,n)•Bremsstrahlung + W or Pb (prompt photo-neutron)•Bremsstrahlung + DU (photofission, delayed neutrons)•D-T generator (14 MeV neutrons slowing to thermal)Different moderators•Polyethylene•Paraffin wax•Water•MelamineObject shapes and sizesSingle pixelMultiple separated objectsRound, diameter up to 1/3 field of viewTriangle, rectangle, torus Demonstration of multiple-source counting capability8Pu oxide cans in water jackets at SRLTOP VIEW SIDE VIEW5 cm water is not enough10 cm water gives good thermalization9Imaging experiments at INL• 252Cf sources in three 10 cm polyethylene cubes• The neutron diffusion length is less than the 10 cm cube size so the center cube is suppressed• Agrees with Monte Carlo results (right- Alain Lebrun)R = 3 mAngular resolution ~ 2 deg10Leakage of thermal neutrons from dry storage casks at INL Tech Area NorthThermal neutron imageExamples of storage casks at Idaho National LabKlaus-Peter Ziock, Gus Caffrey, Alain Lebrun, Leon Forman, Peter Vanier and Jason Wharton,Conference Record  of IEEE Nuclear Science Symposium, 2005, Puerto Rico.11Back illumination  with thermal neutronsPhotograph Neutron ImageBPE Shielding Wooden wedgeNeutron sourcebehind paraffin cylinder12Cf-252 or Pu in melamine moderators0100020003000400050006000700080009000100000 20 40 60 80 100 120 140XIntensityA maskB maskC maskDIAMETER13Prompt photoneutrons from high-Z targets• A pulsed electron accelerator produces high-energy x-rays (10-MeV) to generate photonuclear reactions• Nuclear materials will undergo photofission and generate prompt and delayed neutrons• The delayed neutrons continue to be emitted after each prompt neutron emissionD.R. Norman, J.L. Jones, K.J. Haskell, P. Vanier and L. Forman, IEEE NSS-MIC Conference Record, October 23-29, 200514Thermal and epithermal neutron detectionEpithermalneutronThermalneutronCdPEHe-3EpithermalneutronThermalneutronHe-3INL PHOTO-NUCLEAR DETECTOR BARE He-3 DETECTOR15Neutron responses after short pulses of photonsEpithermalNeutron Response for Image 30.11101001000100001000000 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20Time (ms)CountsDU PNDDU Bare He-3W PNDW Bare He-3ThermalTime (ms)              CountsDELAYED IMAGING WINDOWPROMPTMean thermal neutron velocity = 2.2 eters /millisecondU  TARGETW  TARGET16Delayed neutron images0246810121 51 101 151 201 251Relative Neutron Intensity0246810121 51 101 151 201 251Relative Neutron Intensity6 σPIXEL INTENSITYHISTOGRAMSRELATIVE INTENSITY      RELATIVE INTENSITY      NO OF PIXELSNO OF PIXELSDepleted uranium in polyethylene– 6.5-17.5 ms image window– 69k neutrons, mean = 72, σ = 28Tungsten in polyethylene– 6.5-17.5 ms image window– 17k neutrons, mean = 122, σ = 4117Time progression of image and background • Fast neutrons slowed down to thermal energy in 10’s of microseconds• Time-of-flight distribution for source pixel retains Maxwelliandistribution of delayed neutrons from fission in DU+poly target• Background dies away as a function of distance from thermalization materials in sceneBNL and INL time spectra for DU plus poly target101001000100001000000 2 4 6 8 10 12 14 16 18 20Time following accelerator pulse (msec)counts normalized to INL DU bareDU PNDDU BARETHEORY Maxwellian/ delayed nBNL BRIGHT PIXELBNL BCKTIME DELAY AFTER PHOTON PULSE (msec)COUNTS (NORMALIZED TO BARE INL TUBE)DU + POLYETHYLENE TARGET18BNL/INL time spectra of W/poly0.11101001000100001000000 2 4 6 8 10 12 14 16 18 20Time following accelerator pulse (msec)counts norm to W polyW PNDW BARETHEORY Maxwellian/ delayed nBNL BRIGHT PIXELBNL BCKTime progression of image and backgroundTIME DELAY AFTER PHOTON PULSE (msec)COUNTS (NORMALIZED TO BARE INL TUBE)•W+poly target does not produce delayed neutronsBackground overwhelms direct thermals after 4 msNote scale starts 2 decades lower than DU+polyW + POLYETHYLENE TARGET19Interlaced Linac and Detector Gating for Delayed Neutrons00.20.40.60.810 5 10 15 20Time (sec)Linac OperationDetector OperationDelayed Neutrons20Detail of gating schematic 00.20.40.60.8110.9 11 11.1 11.2 11.3 11.4 11.5 11.6 11.7 11.8 11.9 12 12.1Time (sec)Linac OperationDetector OperationDelayed Neutrons2115 Meter Standoff DetectionDU target with poly, 10 min acquisition, gated (delayed) 1080 countsAccelerator distance = 15 mDetector distance = 2.4 m (a 1 m2 detector would have same solid angle at 16 m)Bright spot in 1-second delayed image implies fissionable material 051015202530350 50 100 150 200 250 300IN T EN SIT Y22DU TARGET 15m FROM ACCELERATOR1080 DELAYED THERMAL NEUTRONSMEAN =106SIGMA = 31MAX =2564.7 SIGMA051015202530350 50 100 150 200 250 300INTENSITYNUMBER OF PIXELS23REDUCING BACKGROUND24Recent experiments at Idaho Accelerator Center• Reduced high voltage on He-3 chamber to avoid saturation of preamps• Higher count rates achieved for prompt component• Explored effects of better shielding of accelerator and converter• Explored time gates in the range 0.2 ms to 20 ms • Should be able to reduce backgroundLong time gate Shorter gateMore shieldingExtra shielding25Future work for the remainder of the project• Continued active interrogation experiments at INL • More quantitative estimates of fluxes of  ?photons?fast neutrons?epithermal neutrons?thermal neutrons• Suppression of effects of gamma flash on detector• Time sliced imaging – separating direct signal from background scatter

Thermal neutron imaging support with other laboratories BL06-IM-TNI

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Thermal neutron imaging support with other laboratories BL06-IM-TNI

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