Location and Activity Characterization of Gamma-Ray Point Sources Concealed in Shipping Containers Using Iterative Reconstruction and Modeling Cargo-Specific Attenuation

Simulated measurements of traditional shipping container screening infrastructure based on large-area polyvinyl-toluene (PVT) or sodium-iodide detectors (NaI) are used alongside an iterative reconstruction algorithm to characterize the activity and location a radioactive point source concealed within loaded with cargo. A maximum likelihood expectation maximization method is employed reconstruct distribution under assumption that there exists single in scenario.To account for shielding by cargo, it assumed encompassing which was chosen represent iron such as scrap metal machine parts, homogeneously distributed throughout 32.2-m3 at realistic densities 0.0, 0.2, 0.6 gcm−3. When material properties cargo known provided algorithm, capable localizing 40.5 cm estimating correct order magnitude cases no 0.2 gcm−3 completely filling volume. With density gcm−3, localization estimation significantly worse, attributed accounting attenuation decreased signal-to-noise ratio, use gross-count data include effect buildup radiation. Using 662-keV photopeak from NaI-based radiation portal monitor (RPM) achieves better results than PVT- RPM estimates all densities.For scenarios where unknown, but its known, brute-force search performed find optimum mass coefficient describes From range coefficients obtained, not differentiating between different types common demonstrates principle characterizing Ultimately, largest limiting factor this simple average estimate path length traveled through direction detector. The large area result high variance length, degree exponentially dependent value.Despite (MLEM PS) able well case PVT-based above container, drastically reducing secondary processes. MLEM PS therefore, represents means enhancing procedures without requiring significant changes hardware.