Metrics for Developing an Endorsed Set of Radiographic Threat Surrogates for JINII/CAARS

[摘要] CAARS (Cargo Advanced Automated Radiography System) is developing x-ray dual energy and x-ray backscatter methods to automatically detect materials that are greater than Z=72 (hafnium). This works well for simple geometry materials, where most of the radiographic path is through one material. However, this is usually not the case. Instead, the radiographic path includes many materials of different lengths. Single energy can be used to compute {mu}y{sub l} which is related to areal density (mass per unit area) while dual energy yields more information. This report describes a set of metrics suitable and sufficient for characterizing the appearance of assemblies as detected by x-ray radiographic imaging systems, such as those being tested by Joint Integrated Non-Intrusive Inspection (JINII) or developed under CAARS. These metrics will be simulated both for threat assemblies and surrogate threat assemblies (such as are found in Roney et al. 2007) using geometrical and compositional information of the assemblies. The imaging systems are intended to distinguish assemblies containing high-Z material from those containing low-Z material, regardless of thickness, density, or compounds and mixtures. The systems in question operate on the principle of comparing images obtained by using two different x-ray end-point energies--so-called 'dual energy' imaging systems. At the direction of the DHS JINII sponsor, this report does not cover metrics that implement scattering, in the form of either forward-scattered radiation or high-Z detection systems operating on the principle of backscatter detection. Such methods and effects will be covered in a later report. The metrics described here are to be used to compare assemblies and not x-ray radiography systems. We intend to use these metrics to determine whether two assemblies do or do not look the same. We are tasked to develop a set of assemblies whose appearance using this class of detection systems is indistinguishable from the real threats. To check such an indistinguishability, we must define metrics that are broad enough to cover systems of different source spectra and detector spectral response; in other words, the best metrics should capture physical properties of the assemblies and not the source and detectors employed. In fact, one requirement for the metrics is that, as the detection circumstances change, the similarity or difference of the metrics of two assemblies should be maintained. This report describes the set of two simple 'dual energy' metrics that we have selected. A second report (Wurtz, et al. 2009) goes on to demonstrate several characteristics of the metrics, including how sensitive they are (or are not) to changes in the detection systems, shielding, etc.

[发布日期] 2009-02-11

[学科分类] 物理（综合）

[关键词] 62 RADIOLOGY AND NNUCLEAR MEDICINE;CARGO;DETECTION;ENERGY YIELD;GEOMETRY;HAFNIUM;METRICS;MIXTURES;PHYSICAL PROPERTIES;RADIATIONS;SCATTERING;SHIELDING;SPECTRA;SPECTRAL RESPONSE;THICKNESS;X-RAY RADIOGRAPHY