METHODOLOGY FOR THE MEASUREMENT OF BETA-DECAY INTENSITY DISTRIBUTIONSFROM THE ANALYSIS OF TOTAL ABSORPTION GAMMA-RAY SPECTRA

A total absorption gamma-ray spectrometer (TAGS), based on a 25.4-cm d iameter X 30.5-cm long NaI(Tl) well detector, has been developed at th e INEL on-line isotope separator facility. A Si detector in the well o f the NaI(Tl) detector allows one to collect beta-particle-gated coinc idence gamma spectra in addition to singles gamma spectra. From the an alysis of these total absorption gamma-ray spectra, beta(-)-decay inte nsity distributions are obtained. The analysis methodology is based on response functions that simulate the response of the NaI(Tl) detector to the gamma-rays and electrons (including external bremsstrahlung) f rom a radioactive source in the detector well. These response function s are computed with a Monte Carlo photon and electron transport code. This methodology has been completely upgraded since it was first devel oped and now provides very good simulations of both singles and coinci dence spectra. As an example of the application of this methodology, t he I-beta distribution for the decay of Cs-141 is determined from the TAGS spectra.