EXPERIMENT ON THE PERFORMANCE OF THE NEUTRONBASED EXPLOSIVES DETECTION SYSTEM USING 252Cf AND 241Am/ 9Be
Keywords:
Explosives detection, radioactive source, thermal neutrons analysis, fast neutron analysis, Monte Carlo calculationsAbstract
This experiment used 252Cf and 241Am/ 9Be with activities of 2.215 × 107n/s to test the performance of aneutron-based Explosives Detections System (EDS). The EDS is made up of a box-shaped paraffinmoderator,a thallium-doped sodium iodide gamma-ray detector, and a radioactive neutron source.Various parameters resulted from the inspection of TNT are measured and compared with the correspondingresults from Monte Carlo calculations based on Monte Carlo N-Particle (MCNP) computercode. The following results are obtained: the thermal neutron fluxes at the center of the inspectioncavity, from measurement and calculation, are 68.1 ± 4.9 n/cm2-s and 58.7 ± 7.6 n/cm2-s, respectively; theEDS’s detection sensitivities based on the detection of the 10.8-MeV gamma rays, from measurementand calculation, are 0.53 ± 0.06 cps/kg and 0.62 ± 0.07 cps/kg, respectively; with a collimation of thegamma-ray detector in place, the measured intensity of the 2.2-MeV gamma rays resulted frominteractions of thermal neutrons with H-chemical elements of TNT reduced by 40%; when 241Am/ 9Beis used as the neutron source, the 4.4-Mev gamma rays from C can be observed along with the 2.2- and10.8-MeV gamma rays from H and N, respectively; the measured fractional ratios of NH/NC, NH/NN andNC/NN are 1.44 ± 0.16, 58.06 ± 8.17 and 40.37 ± 4.89, respectively, while their corresponding theoreticalvalues are 1.18 ± 0.12, 50.13 ± 3.51 and 42.42 ± 4.74, respectively; the maximum total doses at 1 m awayfrom the EDS’s surfaces, from the measurement and calculation, are 9.43 ± 0.36 and 10.51 ± 0.53 μSv/h,respectively.
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