Comparison of NaI(Tl) scintillators and high purity germanium for vehicle portal monitor applications

Radiation portal monitors are being deployed at international border crossings to detect illicit transport of radioactive material. Typically, vehicles which have a gamma-ray radiation signature above a certain gross-count threshold proceed through a more thorough inspection to locate and identify the source of radiation. Plastic scintillators (e.g., poly vinyl toluene (PVT)) are the most common gamma-ray detectors for portal monitors, mainly because of their relatively low cost for large-area, high-sensitivity detectors. Plastic scintillators provide gamma-ray detection, but limited spectroscopic information. Sodium iodide [NaI(Tl)] scintillator-based portal monitors can provide isotopic identification and may be useful where isotopic identification is needed. Recently, high purity germanium [HPGe]-based portal monitors have been evaluated since the increased resolution from HPGe can potentially provide isotopic identification more precisely and rapidly if deployed with adequate efficiency.