Beta decay of neutron-rich isotopes of zinc and gallium

Beta-decays of neutron-rich nuclei near the doubly magic ⁷⁸Ni [78Ni] were studied at the Holifield Radioactive Ion Beam Facility. The half-life and the gamma-gamma coincidence spectra were used to study the nuclear structure. A new ^82,83Zn [82Zn, 83Zn] decay-scheme was built, where a 71±7% beta-delayed neutron branching ratio was assigned in ⁸²Zn [82Zn] decay. New gamma-ray lines and energy levels observed in ^82,83Ga [82Ga, 83Ga] beta-decay were used to update previously reported decay-schemes. The experimental results were compared to shell model calculations, which postulate the existence of Gamow-Teller transitions in these decays. The half-lives of 155±17 and 122±28~ms were determined for ^82,83Zn, respectively.

In order to enable future studies of very neutron rich isotopes a new detector was developed as a second project. This detector is intended for use in fragmentation type experiments, which require segmentation in order to enable implantation-decay correlations. In addition, the detector requires good timing resolution for neutron time-of-flight experiments. A Position Sensitive Photo-Multiplier Tube (PSPMT) from Hamamatsu coupled with a 16x16 fast pixelated plastic scintillator was used. The PSPMT's anodes form 8x8 segment panel used for position reconstruction. Position localization has been achieved for energies range of 0.5-5 MeV. A single signal dynode (DY12) shows a sufficient time resolution between this signal and the anode's signals, which enable us to used DY12 signal alone as a trigger for timing purposes. The detector's DY12 signals was tested with reference detectors and it provided a sub-nanosecond time resolution through the use of a pulse-shape analysis algorithm, which is sufficient for use in experiments with the requirement for the fast timing. The detector ability to survive after implanting high-energy ions was tested using a laser that simulated energy of 1 GeV. The recovery time of the detector in this situation was 200 nanosecond.