Systematics of log ft values for β−, and EC/β＋ transitions

Abstract

This work is an update of the 1998 publication by Singh et al. [1] and reviews the log $ft$ values for all the known $\beta$-decay branches ($\beta$−, $\beta$＋/EC). Furthermore, an update of all $Q$-values (from AME2020  [2]), as well as a recalculation of all the log $ft$ values (through BetaShape code [3], [4]) has been conducted using relevant data in the ENSDF database, as well as in newer literature. Only those cases have been considered in this review, where the beta transitions occur between levels of firm single spin assignments (86% of the transitions), and with probable single spin assignments (14% of the transitions), but with firm parity assignments for all the transitions. Weak $\beta$ branches of $<$1% intensity in complex decay schemes have generally been omitted. Out of a total of 26 318 $\beta$ transitions extracted from the ENSDF database and current literature, data for only 4038 $\beta$ transitions survived the filtering criteria in the present review. The log $ft$ values in $\beta$ decay, spanning about 21 orders of magnitude, have been classified into allowed and forbidden categories according to the classification scheme of Konopinski [5]. All log $ft$ values have been deduced using the BetaShape code with new developments presented in this study. A very few number of log $ft$ values for very low-energy beta transitions ($<$5 keV) survived the cut criteria and are briefly discussed in terms of atomic overlap corrections. Also tabulated and briefly discussed are seven superallowed cases with $\Delta$T = 0, T${}_z$(parent) = −2, while a known case for ²⁸S to ²⁸P has been omitted as reliable EC/$\beta$＋feeding to the analog state in ²⁸P cannot be assigned due to lack of adequate experimental and detailed data for this decay. Centroid, width, minimum and maximum values for each category have been deduced. Uncertainties have been estimated and are also given. For literature coverage in the present review, see discussion in text.