Spectroscopic and non-spectroscopic radiation portal applications to border security

Countries around the world are deploying radiation portal monitor (RPM) systems and other radiation detection instrumentation to interdict the illegal shipment of radioactive material crossing international borders. These efforts include deployments in the U.S. and in a number of other countries by governments and international organizations. Because of their high efficiency for gamma-ray detection, most deployed RPM systems are based on plastic scintillators. Such systems, however, are largely non-spectroscopic in capability. Fully capable spectroscopic portal monitor (SPM) systems are undergoing engineering development for deployment in the near term. These SPM systems are mostly based upon NaI(Tl) gamma ray detector technology and include the ability to identify the detected radioisotopes under many conditions. This identification capability may allow improved operational handling of radiation alarms, particularly those arising from the normal cargo stream of naturally occurring radioactive material (NORM), commercial radioactive sources, and individuals treated with medical radiopharmaceuticals. The goal for improved RPM systems, whether they are spectroscopic or non-spectroscopic, is to increase the sensitivity to threats while reducing the impact that nuisance alarms have on operations. Four hypotheses about radiation screening at borders are conjectured