Speaker
Description
Theoretical and experimental studies on the beta decays of the most prominent fission products in nuclear reactors are needed to unravel the source of the anomalies detected in the related anti-neutrino flux. One of these fission products, 92Rb, was recently studied for its beta decay to 92Sr by using large-scale nuclear shell-model (NSM) calculations to analyze the role of forbidden beta transitions in the theoretical prediction of the total electron spectral shape. Our calculations of the total electron spectrum rely on experimental branching data obtained from a recent TAGS (Total Absorption Gamma Spectroscopy) of the same isotope. These branchings are used for pinpointing the effective values of the weak axial-vector coupling $g_{\rm A}$ and the mesonic enhancement factor ($\varepsilon_{\rm MEC}$). Our calculations take into account all allowed and forbidden decay transitions, making it a pioneering study of the total spectral shape for a beta decay with a high decay Q value. We show that the first-forbidden non-unique transitions can be behind the so-called 'bump' in the measured reactor anti-neutrino flux. Considering this is one of the many important isotopes, further studies on the spectral shapes are called for. Our main interest is to show the necessity of further studies of the beta decays of the most prominent isotopes contributing to the anti-neutrino flux, and additionally to show the necessity to further understand the role of $g_{\rm A}$ in the building of the total electron spectral shape.
