A multiple-detector Radioactive Material Detection Spectroscopic (RMDS) portal

This paper describes an optimization process for a Radioactive Material Detection Spectroscopic (RMDS) portal, designed to detect and identify radioactive materials concealed inside cargo containers. The system is based on a combination of conventional 3 in. NaI(Tl) gamma detectors and 3He neutron detection tubes. The basic concept and the advantages of the new segmented spectroscopic detector approach are presented with several algorithms that were developed to enhance the detection capability of the portal and improve the signal to noise ratio. The results of field tests performed in several locations in Israel are also presented. The RMDS portal fully meets the demands of new ANSI Standard 42.38 for spectroscopic portals. In addition, the portal has some unique features, such as the ability to find the exact location of a point source inside the cargo and the ability to differentiate between a point source and Naturally Occurring Radioactive Materials (NORM) radiation. During the tests, the RMDS portal was compared to other detection systems, such as a PVT-based portal and a handheld spectroscopic HPGe detector. In these tests, the RMDS system was found to have a unique technique for background subtraction, which results in a higher detection sensitivity.