Gamow-Teller transitions to 64Cu measured with the 64Zn(t,3He) reaction

The Zn-64(t,He-3) reaction has been studied by using a secondary triton beam of 115 MeV/nucleon to extract the Gamow-Teller transition-strength distribution to Cu-64. The results were compared with shell-model calculations with the pf-shell effective interactions KB3G and GXPF1A and with existing data from the Zn-64(d,He-2) reaction. Whereas the experimental results exhibited good consistency, neither of the theoretical predictions managed to reproduce the data. The implications for electron-capture rates during late stellar evolution were investigated. The rates based on the theoretical strength distributions are lower by factors of 3.5-5 compared to the rates based on experimental strength distributions.