Creation of realistic radiation transport models of radiation portal monitors for homeland security purposes

Much of the data used to analyze and calibrate alarm algorithms for radiation portal monitor (RPM) systems has come from actual measurements of vehicles passing through RPMs. Due to the inherent limitations and expense of taking data with controlled radioactive sources, the majority of these data contain no sources except for naturally occurring radioactive material (NORM) cargo sources in the presence of natural background. Advances in computing capabilities have made it feasible to simulate "in-the-field" detector responses from a wide variety of source/cargo configurations, and to produce data matching that generated in the field. Computational models have been developed by the Radiation Portal Monitor Project (RPMP) for many detectors, vehicles, cargo configurations, and sources. These models are being used to simulate RPM responses to complicated source/cargo configurations for vehicles with and without sources. The simulated data is, and will be used to 1) complement existing field data, 2) help guide the progress of future data taking, 3) improve our ability to calibrate and refine alarm algorithms, 4) verify the causes of effects seen in the field, and 5) look for unknown effects not corresponding to theoretical models. A large set of simulated data that has been validated against field data will allow for in-depth testing of detection alarm algorithms for a variety of source scenarios. An overview of the PNNL/RPM Modeling System will be presented. Highlights from selected results already obtained and compared to data will be shown, and a set of ongoing cases being simulated will be outlined.