Technical Advice and Support for the Joint Integrated Non-Intrusive Inspection (JINII) Program Task 2.2 Transmission Digital Radiography (DR)

[摘要] The Cargo Advanced Automated Radiography System (CAARS) program aims to utilize advanced radiographic systems to detect radiological and nuclear threats. Validation of initial design and testing concepts is a precondition for prototype system development and large-scale deployment. As expected, Depleted Uranium (DU) is a valid surrogate for Special Nuclear Materials (SNM) in CAARS Advanced Technology Demonstration (ATD) performance field-tests of transmission radiography systems. Dual-energy transmission measurements of DU are nearly identical to SNM, and are distinct from lower Z materials, provided the samples are matched to equal areal density. Results from an alternative method, using samples of equal thickness, showed sample discrimination by material density, rather than by atomic number (Z). The transmission measurements of DU and SNM were made with equipment that is nearly identical to current field systems. X-ray source beams at endpoint energies of 5.4 MeV and 9.6 MeV were used to measure transmission through the selected sample materials. The ratio of the x-ray linear attenuation coefficient times length ({micro}L) at 5.4 MeV, to {micro}L at 9.6 MeV is a metric for atomic number based discrimination of materials. The measured ratios were compared with computed values based on LLNL photon cross section data and LLNL developed models of x-ray detector characteristics. Measured ratios for DU differed from HEU by an average of 0.25%, and from WGPu by 0.08%, which is within the noise level of 0.4 to 0.5%. For comparison, measured ratios for Sn differed from HEU by 3.2%, and from WGPu by 3.6%, well beyond the measurement noise. Measured ratios for W differed from HEU by 0.01%, and from WGPu by 0.32%. The measured ratio values presented in Table 1 demonstrate the feasibility of using a threshold ratio to discriminate low-Z (Z < 72) from high-Z (Z {ge} 72) materials (as defined by CAARS specification). In the case of our test system, a threshold ratio of 1.08 would be suitable based on the measured results.

[发布日期] 2011-03-03

[学科分类] 物理（综合）

[关键词] ATOMIC NUMBER;ATTENUATION;CARGO;CROSS SECTIONS;DEPLETED URANIUM;DESIGN;FIELD TESTS;LAWRENCE LIVERMORE NATIONAL LABORATORY;METRICS;PERFORMANCE;PHOTONS;TESTING;THICKNESS;VALIDATION;X-RAY SOURCES