The Development of Large-area Plastic Gamma-ray Spectrometers

Although large-volume plastic scintillation detectors have been widely used in Homeland Security applications for the detection of potential radiological and nuclear threats using cargo portals, they generally provide little or no spectroscopic information. Such information is key to the achievement of reduced nuisance-alarm rates. This paper outlines the improvements that have been achieved in the design and performance capability of large-volume PVT scintillation counters. In particular, they have an improved light-collection efficiency and uniformity of response. This improvement has been important in making it feasible to use Symetrica's spectrum-processing algorithms in order to provide an accurate estimate of the gamma-ray spectrum that is incident on the detectors. Such spectra have then been used as the input to an isotope-identification algorithm. This paper provides an indication of how the certainty of the isotope identification depends both on the number of lines in the spectrum and the total number of counts recorded. In view of this progress, we believe that large PVT detectors will soon be able to provide a very useful degree of isotope specificity in addition to their high detection-sensitivity.