BETA-RAY SPECTROSCOPY BASED ON A PLASTIC SCINTILLATION DETECTOR SILICON SURFACE-BARRIER DETECTOR COINCIDENCE TELESCOPE

Beta radiation is now recognized as a significant radiation safety pro blem and several international conferences have recently been devoted to the problems of mixed field beta/photon dosimetry. Conventional dos imetry applies algorithms to thermoluminescence dosimetry (TLD) multi- element badges which attempt to extract dose information based on the comparison of TL signals from ''thick/thin'' and/or ''bare/filtered'' elements. These may be grossly innacurate due to inadequate or non-exi stant knowledge of the energy spectrum of both the beta radiation and the accompanying photon field, as well as other factors. In this paper , we discuss the operation of a beta-ray energy spectrometer based on a two-element, E xdE detector telescope intended to support dose algor ithms with beta spectral information. Beta energies are measured via a 5 cm diameter x2 cm thick BC-404 plastic scintillator preceded by a s ingle, 100 mu m thick, totally depleted, silicon dE detector. Photon e vents in the E detector are rejected by requiring a coincidence betwee n the E and dE detectors. Photon rejection ratios vary from 225:1 at 1 .25 MeV (Co-60) to 360:1 at 0.36 MeV (Ba-133). The spectrometer is cap able of measuring electron energies from a lower energy coincidence th reshold of approximately 125 keV to an upper limit of 3.5 MeV. This en ergy range spans the great majority of beta-emitting radionuclides in nuclear facilities.