The ${}_{}{}^{67}{}_{}{}^{}\mathrm{Se}$ and ${}_{}{}^{68}{}_{}{}^{}\mathrm{Se}$ isotopes near the proton drip line were produced by spallation of zirconium with 600 MeV protons at CERN. Beta decay properties were determined for the first time using the selectivity of molecular ion beams at the on-line mass separator ISOLDE. Chemically selective production was obtained through separation of the molecular ion ${\mathrm{COSe}}^{+}$. The half-lives of ${}_{}{}^{67}{}_{}{}^{}\mathrm{Se}$ and ${}_{}{}^{68}{}_{}{}^{}\mathrm{Se}$ were measured as 107±35 ms and 35.5±0.7 s respectively. From β-γ and γ-γ coincidences, and conversion-electron measurements, a decay scheme was obtained for ${}_{}{}^{68}{}_{}{}^{}\mathrm{Se}$. For the ${}_{}{}^{68}{}_{}{}^{}\mathrm{As}$ ground state and several excited states, spin and parity are unambiguously determined from β-decay rates and electromagnetic multipolarity assignments. In addition to the strong Fermi branch between the mirror ground states of ${}_{}{}^{67}{}_{}{}^{}\mathrm{Se}$ and ${}_{}{}^{67}{}_{}{}^{}\mathrm{As}$ [${\mathit{J}}^{\mathrm{\pi }}$=(5/2${)}^{\mathrm{-}}$,${\mathit{T}}_{\mathit{z}}$=±1/2], a GT branch to an excited state in ${}_{}{}^{67}{}_{}{}^{}\mathrm{As}$ is observed. Implications of ${}_{}{}^{67}{}_{}{}^{}\mathrm{Se}$ and ${}_{}{}^{68}{}_{}{}^{}\mathrm{Se}$ properties in the rp-process path are considered.

• Received 21 March 1994

DOI:https://doi.org/10.1103/PhysRevC.50.1180