l-forbidden Gamow-Teller β decay ofCu57

Absolute branching ratios for the β decay of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Cu}$ to excited states up to 3.3 MeV in ${}_{}{}^{57}{}_{}{}^{}\mathrm{Ni}$ have been determined, including the l-forbidden Gamow-Teller transition to the first excited state in ${}_{}{}^{57}{}_{}{}^{}\mathrm{Ni}$. Four transitions to excited states at 0.768, 1.113, 2.443, and 3.007 MeV are observed in addition to the superallowed decay to the ground state of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Ni}$. The measured branching ratio to the ground state is 89.9 ± 0.8% and the branching ratios to the four excited states are 0.94 ± 0.09%, 8.6 ± 0.6%, 0.17 ± 0.03%, and 0.35 ± 0.04%, respectively. In addition we have measured the ${}_{}{}^{57}{}_{}{}^{}\mathrm{Cu}$ half-life and find it to be 196.3 ± 0.7 ms, which is in good agreement with the most recent measurement. B(GT) values have been extracted from the new results and are compared to shell model calculations. © 1996 The American Physical Society.