Neutron Based Techniques for the Detection of Illicit Materials and Explosives

Transcription

1 Neutron Based Techniques for the Detection of Illicit Materials and Explosives R. E. Mayer, A. Tartaglione, J. Blostein,, C. Sepulveda Soza M. Schneebeli,, P. D Avanzo,, L. Capararo Neutron Physics Group and Instituto Balseiro Comisión n Nacional de Energía a Atómica and Universidad Nacional de Cuyo also at CONICET ARGENTINA also at CCHEN, CHILE IAEA CRP F South Africa 2009

2 IAEA CRP CODE F Research Agreement Slow Neutron Interrogation for Detection of Concealed Substances IAEA South Africa 2009

3 Graduate Student Work A.Tartaglione, PhD Thesis F.Di Lorenzo, PhD Thesis C.Sepulveda Soza,, Master in Engng. Thesis at Instituto Balseiro (CNEA and Univ.Nac.de Cuyo) ARGENTINA IAEA South Africa 2009

4 APPLICABILITY OF MODERATED NEUTRONS Efforts to test slow neutron based techniques aimed at detecting and identifying illegal substances, including explosives, are carried out at the electron linear accelerator facility in Bariloche,, Argentina, as part of graduate student research work. Preliminary results show : A capacity to detect several substances through pulsed neutron induced prompt gamma emission and to reveal the presence of special nuclear material (SNM) through detection of fission neutrons. Time of flight and slow neutrons are employed taking advantage of higher capture cross sections at low energy. IAEA South Africa 2009

5 APPLICABILITY OF MODERATED NEUTRONS Slow neutron time of flight (TOF) was tested for position determination of a target test object placed at different positions over realistic distance range (within 2 m). As much effort is devoted elsewhere through the use of fast neutron induced reactions, we seek to explore a complementary path by means of testing the applicability of moderated neutrons. These, although not penetrating thick objects as a beam, they do diffuse into substances. Overcoming reduced neutron penetration due to a surrounding thick hydrogenated matrix, was explored through alternative irradiation with fast neutrons and the ensuing moderation inside the matrix, although with loss of TOF information IAEA South Africa 2009

6 PART ONE SUBSTANCE IDENTIFICATION THROUGH SLOW NEUTRON INDUCED GAMMA RESPONSE Thermal and epithermal components distinguished through neutron TOF IAEA South Africa 2009

7 PART ONE INITIAL RESULTS GAMMA SPECTRA FROM SOME SAMPLES IN FAVOURABLE CONDITIONS IAEA South Africa 2009

8 Gamma Spectrum 1 thermal neutron absorption epithermal neutron absorption Fe; 6018,53 kev(de) 56 Fe; 6018,53 kev(se) 0.1 1E- 3 1E- 4 1E Fe; 6018,53 kev 1E Fe; 691,96 kev 1E a.u. 1E-3 56 Fe; 1260,44 kev 56 Fe; 352,35 kev 1E-4 1E E [kev] Fe sample,, 6 mm thick

9 Gamma Spectrum 0.1 ee + aniq.; 511 kev thermal neutron absorption epithermal neutron absorption S; 840,993 kev 1E-3 a. u. 1E-4 1E-5 1E E [kev] S sample,, 140 g

10 Gamma Spectrum 1 therma l neutron absorption epithermal neu tron abso rption 35 Cl; 517,073 kev 0.1 ee + aniq; 511 kev 35 Cl; 788,8 kev 35 Cl; 1164,86 kev a.u ( 35 Cl; 1601,072 kev ) 35 Cl; 1951,14 kev 1E-3 1E E [kev] Cl in NaCl sample,, 215 cm 3

11 Gamma Spectrum Ag - 117,45 kev (Th abs. table) 109 A g - 198,72 kev (Th abs. table) thermal neutron absorption epithermal neutron absorption Counts / Monitor ? 109 Ag - 549,56 kev (Th abs. ta ble) E γ [kev] Ag sample,, mm thick sheet

12 NITROGEN DETECTION 0,1 0,01 Iron Nitrogen and iron Iron only Nitrogen selected ROI 1E-3 a.u. 1E-4 Nitrogen 1E-5 Iron selected ROI E (MeV) Irradiated LN2 mass = 100,9 g

13 NITROGEN DETECTION Sensitivity to N/Fe 0,024 0,022 0,020 Nitrogen ROI/Iron ROI Iron and nitrogen Iron without nitrogen Iron and water a.u. 0,018 0,016 0,014 0,012 0,010 0,008 0,006 0, "time" 5 min irradiations. Irradiated LN2 mass = 100,9 g

14 PART ONE INITIAL RESULTS TOF POSITION SENSITIVITY OF SAMPLE GAMMA RESPONSE IN ABSENCE OF CONCEALING CARGO IAEA South Africa 2009

15 POSITION DETERMINATION TOF through capture gammas in sample. 4 NaI(Tl) array 6 1kg NaCl LARGE MOVEMENT a.u. 4 6 m flight path 7 m flight path 8 m flight path Time-of-flight (µs)

16 PART TWO URANIUM DETECTION THROUGH SLOW NEUTRON INDUCED FISSION RESPONSE IAEA South Africa 2009

17 INITIAL TESTS Initial work was aimed at identifying a way to detect the presence of SNM, testing the applicability of slow neutron irradiation for that purpose. TOF is also tested as a method to find the SNM position inside a concealing array of neutron scattering cargo. IAEA South Africa 2009

18 Initial (basic) Experimental setups Test if observed signal is caused by thermal neutrons 0,1 HEU HEU and Cd filter Normalized Counts 0,01 1E-3 1E-4 1E Time of Flight [ms]

19 Initial (basic) Experimental setups Test if signal is fission 0,1 0,01 HEU Al sample Pb sample Normalized Counts 1E-3 1E-4 1E Time of Flight [ms]

20 The partial Fuel Bundle (FB) Number of fuel pins= 13 Total UO 2 mass= 6.05 kg 235 U mass= g Probable irradiated fraction= ~ 1/10

21 Enriched uranium sample diluted in aluminium Four plates in expanded configuration on a board. 235 U mass= 27.5 g Total sample mass=152.8g 18% U-235 in Al Max.U-235 irradiated by direct beam= 10.7g

22 New Experimental setups 2 m merchandize thickness (considerably hydrogenated)

23 New Experimental setups Sum of Raw Spectra pc40cmHEU 1pc40cmFB 1pc60cmHEU 2pc60cmHEU PCsBackground Time of Flight [ µs ]

24 Experimental Figures-of-Merit FOM [Integral Upper Limit Influence] CPU+UAE*(40cm)+PCs 1CPU+EC(40cm)+PCs 1CPU+UAE*(60cm)+PCs 2CPUs+UAE*(60cm)+PCs To produce integral results that represent each sample condition, the TOF spectra have to be integrated. Influence of lower and upper integration limits are studied through Figures-of-Merit (FOM) to enhance results contrast Upper Limit [µsec] 9 S= Σ Sample/MonitorS Bg= Σ Background/MonitorBg FOM = [S - Bg ] / [(σ S) 2 (3σ Bg) 2 ] 1/2 FOM [Integral Lower Limit Influence] CPU+UAE*(40cm)+PCs 1CPU+EC(40cm)+PCs 1CPU+UAE*(60cm)+PCs 2CPUs+UAE*(60cm)+PCs Lower Limit [µsec]

25 Integral Results 5 minute irradiations (at 200 n/cm 2 /sec) 0,090 0,085 Normalized Integral Counts 0,080 0,075 0,070 0,065 0,060 0,055 0,050 0,045 1CPU+HEU*(40cm)+PCs 1CPU+FuelB(40cm)+PCs 1CPU+HEU*(60cm)+PCs 2CPUs+HEU*(60cm)+PCs PCs Background Mean Background 4 SIGMA Background + 4 Sigma Level 0, Individual Measurements

26 The 4 σ level suggested by IAEA-TECDOC TECDOC-1312 (2002) has not been difficult to attain by any of the 5 minute irradiations with a narrow weak incident beam, in the midst of a thick scattering cargo array and with SNM mass well under 30g. Tests with densely scattering and absorbing media are a natural next step. Unusually high neutron absorption should be detected by the prompt gamma detector array. If cargo has undergone X-ray X scanning as an initial screening, neutron interrogation would be called in to verify merchandize composition.

27 PART TWO TEST SNM POSITION DETERMINATION THROUGH SLOW NEUTRON TIME-OF-FLIGHT IAEA South Africa 2009

28 HEU Position HEU sample to detector distance - 90 cm displacement Normalized Counts [a.u.] Normalized Counts [a.u.] 0,010 0,008 0,006 0,004 0,002 0,000 0,0008 0,0007 0,0006 0,0005 0,0004 0,0003 0,0002 0,0001 0,0000 0,5 0,6 0,7 0,8 0, Time of Flight [ms] HEU-detector 45 cm HEU-detector 135 cm

29 In a clean situation (low scattering), TOF is useful to locate the approximate depth at which SNM is placed in the container slice being investigated. In the worst imaginable situation of densely hydrogenated cargo, TOF would be rendered useless and detection of SNM, as expected, turns increasingly difficult in the midst of low neutron transmission cargo. IAEA South Africa 2009

30 PART THREE TEST WIDE AREA FAST NEUTRON DETECTORS AND LIMITS OF DETECTION FOR Cl AND U IAEA South Africa 2009

31 Experimental setups with Wide Area Detectors 2 m merchandize thickness (considerably hydrogenated) 70 cm x 100 cm active area neutron detector

32 Integral Results for Chlorine 5 minute irradiations (at 200 n/cm2/sec) 50 mm neutron beam Normalized Cl Pulse Height ROI 1,8 1,6 1,4 1,2 1,0 0,8 0,6 1 Kg NaCl in 20 l H 2 O 1 Kg solid NaCl Simulated Cargo Three 25 l Cans of Water Background (no sample) S A M P L E S Normalized Cl Pulse Height ROI 2,0 1,8 1,6 1,4 1,2 1,0 0,8 4 NaI(Tl) array 2 Kg NaCl in 20 l H 2 O 1 Kg NaCl in 20 l H 2 O 0.5 Kg NaCl in 20 l H 2 O Background (no sample) Simulated Cargo Sample only Empty Cans S A M P L E S IAEA Southafrica 2009

33 Transmission Results Transmission (relative to empty container) 0,3 0,2 0,1 0,0 Merchandise Transmission PCs PC monitors Paper reams Number of Units IAEA Southafrica 2009

34 Integral Results for HEU Mean value of 5 minute irradiations Uncertainty smaller than symbols HEU hidden among PC monitors Integral Neutron Counts (normalized by neutron monitor, a.u.) 0,3 0,2 0,1 HEU integral fission neutron counts Background (no HEU) 1E-6 1E-5 1E-4 1E-3 0,01 0,1 1 Container Load Neutron Transmission Integral Neutron Counts (normalized by neutron monitor, a.u.) 0,5 0,1 Container Load: PCs and PC monitors HEU integral fission neutron counts Background (no HEU) 0, Depth into container load [cm] IAEA Southafrica 2009

35 FINALLY PRESENT SITUATION IAEA South Africa 2009

36 Having the sample 6 to 8 m away from the target mimics a smaller neutron source. The low intensity falling on the sample : 200 thermal n/cm 2 /sec and 90 near epithermal n/cm 2 /sec (above cadmium cut-off energy) 40 mm thick polyethylene slab neutron moderator This reduced flux and the limited amount of sample irradiated by the 50mm neutron beam, allowed most experiments to be carried out during 5 min counting times with the described detectors.

37 The thermal vs. epithermal interrogation through the Cd difference method allows better substance identification and also helps confirm that fission is being detected. In moderate scattering arrays, TOF provides approximate information about SNM position. High slow neutron fission cross section allows the 4 σ level to be reached even for samples in the tens of grams range. Delayed neutron emission can be added as a confirmation tool at no extra cost.

38 As a consequence The beam and the neutron detector should be extended to cover a much increased portion of viewed container slice, retaining the sensitivity achieved. Screening against dangerous contraband through investigation of realistic volumes, like a container slice put in evidence by previous X-ray X scanning, seems promising even with a small incident thermal/epithermal neutron flux. Combination with fast neutron irradiation that moderates inside cargo should enhance capability.

39 Thank you Good bye

40 IAEA South Africa 2009