Beta Decay in The Region Of Neutron-Deficient $^{69,70,71}$Kr
Résumé
Proton-rich nuclei beyond the N = Z line play a key role in our understanding of astrophysics, weakinteraction physics, and nuclear structure. The decay of 69Kr (Tz = −3/2) is of particular interest as it populates states in the proton-unbound nucleus 69Br, critical to the rapid proton-capture (rp) process thought to power type I x-ray bursts. During the astrophysical rp process, 2p-capture reactions through 69Br can bypass the "waiting-point" nucleus 68Se [1]. The bypass-reaction rate depends strongly on the proton-capture Q value. A -decay experiment was conducted at GANIL which utilized implant- -proton and - correlations to study nuclear structure and decay properties primarily related to the decays of 69,70,71Kr. Neutron-deficient isotopes ranging from Zn to Kr were implanted into a Si-DSSD detector located at the focal plane of the LISE spectrometer in which spatially and temporally correlated implantation and decay events were studied. Gamma rays were detected in surrounding EXOGAM high-purity germanium clover detectors. We measured -decay half lives for 69,70,71Kr of 27(3) ms, 40(6) ms, and 92(9) ms, respectively, and identified approximately 200 69Kr implantation-decay events. We observed a dominant -decay branch to the isobaric analog state (IAS) in 69Br which then decays to the first excited state in 68Se, a decay path which strongly constrains the spin and mass of 69Kr. Our measured IAS energy, however, disagrees by approximately 1 MeV from the previously adopted value of 4.07(5) MeV [2]. Data from this work represents new measurements that are valuable for updating ENSDF, RIPL, and decay databases, as well as for clarifying existing ambiguities. An overview of the results from our analysis of implanted neutron-deficient nuclei and their implications will be presented.