COULOMB MATRIX ELEMENTS FROM BETA-GAMMA(CP) CORRELATION MEASUREMENTS IN 57NI AND 65NI

Measurements of the β-γ(CP) correlation have been made for the 3 2- (β+, 0.84 MeV) 3 2- (γ, 1.38 MeV) 7 2- (ground-state) cascade in the decay of 57Ni and for the 5 2- (β-, 1.02 MeV) 5 2- (γ, 1.12 MeV) 3 2- (ground-state) cascade in the decay of 65Ni. The values obtained for the 57Ni and 65Ni asymmetry parameters are A = +0.071±0.011 and A = +0.23±0.04, respectively. The 57Ni results verify the shell-model prediction of 3 2 for the spin of the 57Ni ground state. Thus, both cases are mixed β-transitions, and our measurements determine values for the Coulomb matrix elements connected with the Fermi part of the decays. The Coulomb matrix elements are 54±10 keV for 53Ni and 3.6±5.7 keV for 65Ni. A theoretical calculation in the case of 57Ni indicates that the anti-analogue state is mixed to a small extent into the ground state of 57Ni, which could account for the relatively large matrix element. The zero or near-zero matrix element in the case of 65Ni is consistent with a vibrational-quantum number change of one in the β-decay to 65Cu which corresponds to a difference in this same quantum number between the mixing states. © 1968.