Total absorption gamma-ray spectrometer for measurement of beta-decay intensity distributions for fission product radionuclides

Abstract

A total absorption γ-ray spectrometer (TAGS), based on a 25.4 cm diameter × 30.5 cm long NaI(Tl) well detector, has been developed at the INEL on-line isotope separator facility. A Si detector in the well of the NaI(Tl) detector allows one to collect β-particle-gated coincidence spectra as well as singles spectra. With this system, measurements of the total absorption spectra have been made for a number of fission product nuclei. The analysis of the measured spectra is based on response functions for single γ rays that are computed with a Monte Carlo code. Routines have been written to use these response functions to simulate the response to a cascade of several γ rays and by extension to a whole decay scheme. The bremsstrahlung from a ground-state β branch can also be simulated. The quality of the simulation is demonstrated for test spectra of 137Cs, 24Na, 60Co, and 110mAg. As examples of the operation of this system, the measurements and analyses of the β-decay feeding distributions are described for the decay of 141Ba, 139Cs and 140Cs.