Thermal neutron capture studies in five isotopes of selenium

Abstract

<p>The gamma ray spectra associated with thermal neutron capture in targets of ⁷⁶ ⁷⁷ ⁷⁸ ⁸⁰ ⁸²Se have been observed with a high sensitivity pair-spectrometer. Parameters to describe each resolved component are estimated from the measured data. Removal of impurity contributions allows individuals transitions to be attributed to each of the capture reactions. The main application of this information is to reveal details of the structure of the product nuclides. This is realized by the construction of the five radiative decay schemes. Energies and decay modes of quantum states are surmised and new levels are proposed. Optimization of the level energies, and final neutron binding energy, Sn, enhances the precision of previous values. This work produces a three-fold increase in the number of high energy transitions attributed to the larger cross section targets (A=76,77,80), and an order of magnitude enhancement of the transition data for ⁷⁸Se(n,ϒ), as well as the first Identification of transitions in the ⁸²Se(n,ϒ)⁸³Se reaction. In the last case, the value of Sn disproves the long accepted result. The development of Bayesian deconvolution made this extensive analysis feasible. Adapting this technique for Ge(Li) pair-spectra entailed the invention of an automatic continuum removal algorithm and the development of codes for automatic peak analysis. These tools are described in some detail. The art of construction decay schemes from gamma ray data is refined through a new system of procedure to discriminate against the inclusion of false cascades. Several of the measurement techniques described here are pertinent to quantitative studies in other fields.</p>