Decays ofKr72andKr73

Delayed $\gamma$ rays following the decay of two new proton-rich Kr isotopes have been observed. These isotopes were produced by the bombardment of ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ with ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ ions, and were separated from contaminant activities by a gas-transfer system. ${}_{}{}^{72}{}_{}{}^{}\mathrm{Kr}$ decays with a half-life of 17.4 ± 0.4 sec to states in ${}_{}{}^{72}{}_{}{}^{}\mathrm{Br}$, with the subsequent emission of six $\gamma$ rays. ${}_{}{}^{73}{}_{}{}^{}\mathrm{Kr}$ decays with a half-life of 25.9±0.6 sec to states in ${}_{}{}^{73}{}_{}{}^{}\mathrm{Br}$, and emits eight $\gamma$ rays. Identification of the Kr isotopes was based both on the buildup of their daughters, and on relative intensities of decay $\gamma$ rays observed at two different ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ bombarding energies. Decay schemes are presented, and the astrophysical significance of ${}_{}{}^{72}{}_{}{}^{}\mathrm{Kr}$ is discussed.