Mass and beta decay of the N = Z isotope 68Se

An experiment to measure the mass and beta decay of the N = Z nuclide 68Se was performed. The properties of 68Se are important for determining the abundance of proton-rich nuclei such as 60Ni and 64Zn, which are thought to be formed in the alpha-rich freezeout stage of a giant star. The abundances of the even-even N = Z nuclei such as 60Zn, 64Ge, and 68Se depend on the competition between (α,γ) and (γ,α) reactions, whose rates depend sensitively on the reaction Q-values. In addition, the half-life of 68Se is important in determining the path of the explosive rp-process, since reactions such as (p,γ) must compete with beta decay in order to push the rp path to heavier nuclei. Using the moving tape collector system and the 12C(58Ni,2n)68Se reaction at 200 MeV, recoils were mass-selected by a slit at the FMA focal plane and implanted into the tape. After a 50-second collection period, the accumulated activity was moved to the counting position between two Ge gamma-ray detectors or a plastic scintillator beta detector and a Ge detector. The half-life of 68Se was determined to be 37 ± 5 s, in agreement with other measurements. Gamma-gamma and beta-gamma coincidence data are under analysis, to produce the decay scheme and the electron capture decay energy