Methodology for the measurement of β−-decay intensity distributions from the analysis of total absorption γ-ray spectra

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 γ spectra in addition to singles γ spectra. From the analysis of these total absorption γ-ray spectra, β − -decay intensity distributions are obtained. The analysis methodology is based on response functions that simulate the response of the NaI(Tl) detector to the γ-rays and electrons (including external bremsstrahlung) from a radioactive source in the detector well. These response functions are computed with a Monte Carlo photon and electron transport code. This methodology has been completely upgraded since it was first developed and now provides very good simulations of both singles and coincidence spectra. As an example of the application of this methodology, the I β distribution for the decay of 141 Cs is determined from the TAGS spectra.