Abstract
An anticoincidence shielded gamma-ray spectrometer has been designed from a 34 cm dia. by 31 cm thick NaI(Tl) ingot which surrounds an 18 cm dia. by 22 cm thick NaI(Tl) principal detector. The spectrometer and the principal crystal are hermetically sealed in a single container. Low background construction materials, as well as low 40K content phototubes, serve to reduce the background. The low 40K phototubes reduced the 40K detected by the principal crystal approximately twofold compared to standard glass phototubes. The background in the energy range from 0.1 to 3 MeV was reduced from two- to fivefold by the anticoincidence shield. The efficiency of the system for a point and a 70 ml source is approximately fivefold greater than that of a 7.5 cm dia. by 7.5 cm thick NaI(Tl) crystal. By means of the anticoincidence crystal, the Compton edge for 137Cs was reduced by 2.5-fold to produce a peak-to-Compton edge ratio of approximately 160: 1. The system has been utilized for low-level radionuclide analyses of single gamma-ray emitters and has been compared to NaI(Tl) multidimensional and Ge(Li) gamma-ray spectrometers.
Published Version
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