Nuclear matrix elements for the beta decay of 198Au and 122Sb

Abstract

All presently available experimental data on the spectrum shape factor, β-gg directional correlations, β-circularly polarized γ-correlations, and angular distribution of γ-rays from oriented nuclei in the first-forbidden beta transitions of 198Au and 122Sb to the first excited states in 198Hg and 122Te, respectively, have been used to obtain the nuclear matrix elements parameters x, u, ξ′ y, w and ξ′ v. The analysis was based on the theoretical expressions given by Morita and Morita using exact electron radial wave functions which include finite nuclear size corrections. In the case of 198Au, a unique set of parameters was found, but for 122Sb, two sets of parameters were found that fit the data equally well. These parameters are: for 198Au, x = 0.047±0.006, u = −0.097±0.008, ξ′ y = −1.95±0.21; w = 0.20±0.09 and ξ′ v = −4.23±1.26; for 122Sb, Set I, x = −0.06±0.06, u = 0.08±0.10, ξ′ y = 1.15±0.57, w = 4.83±0.55 and ξ′ v = −54.7±5.8; Set II, x = 0.01±0.05, u = 0.10±0.11, ξ′ y = 0.06±0.6, w = 2.47±0.50 and ξ′ v = −29.3±5.8. However, it is shown that in the case of 122Sb, a determination of β-circularly polarized γ-correlation as a function of energy can eliminate one set. For both 198Au and 122Sb, the observed values of the matrix elements are not in agreement with single-particle predictions. However, in the case of 122Sb, they are in agreement with the predictions of Kisslinger and Wu.