Beta-Decay Properties Of Se-67,Se-68 And The Astrophysical Rp-Process Path

The 67Se and 68Se 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 COSe+. The half-lives of 67Se and 68Se were measured as 107 +/- 35 ms and 35.5 +/- 0.7 s respectively. Rom beta-gamma and gamma-gamma coincidences, and conversion-electron measurements, a decay scheme was obtained for 68Se. For the 68As ground state and several excited states, spin and parity are unambiguously determined from beta-decay rates and electromagnetic multipolarity assignments. In addition to the strong Fermi branch between the mirror ground states of 67Se and 67As (J(pi) = (5/2)-, T(z) = +/-1/2), a GT branch to an excited state in 67As is observed. Implications of 67Se and 68Se properties in the rp-process path are considered.