Abstract
This thesis presents the first results using the FAst TIMing Array (FATIMA) spectrometer for electromagnetic transition rate measurements within the NuSTAR facility at GSI-FAIR phase-0. The Monte-Carlo simulated response for gamma-ray detection by FATIMA for exploitation within the the DEcay SPECtroscopy (DESPEC) experimental system at the FAIR Phase-0 facility at Darmstadt, Germany is presented. In this configuration, FATIMA consisted of 36 LaBr₃(Ce) detectors surrounding the AIDA, position sensitive charged-particle active stopper detection system. The decay of the Iπ = 8+ isomerically decaying cascade in ⁹⁶Pd was measured in the first DESPEC experiment at the FAIR-0 facility following the projectile fragmentation of a ¹²⁴Xe primary beam incident on a ⁹Be target and was used to validate the simulations. The experimental data yielded full energy peak efficiency values for FATIMA of 11.2(11)%, 6.8(7)%, 3.8(6)% and 2.1(5)% at 106 keV, 325 keV, 684 keV and 1415 keV respectively, consistent with the values derived from the simulated GEANT4 response. This thesis also reports on the scientific output of the first experiment of the DESPEC Phase-0 campaign at GSI, which focussed on the study of neutron-deficient nuclei approaching ¹⁰⁰Sn. Results are presented on electromagnetic transition rates associated with the decays from excited states populated following the formation of Iπ = 8+ proton ‘seniority isomer’ states in the N = 50 isotones ⁹⁴Ru and ⁹⁶Pd and the Iπ = 14+ isomer in ⁹⁴Pd. Direct half-life measurements via γ−γ coincidences using the FATIMA detector array have been used to determine the reduced matrix elements associated with decays between low-lying states in these semi-magic nuclei. The extracted half-lives for the yrast Iπ = 6+ and 6+ states in ⁹⁶Pd were measured to be 6.4(4) ns and 1.0(1) ns respectively with a prompt decay observed from the 2+ to ground state. Additionally, the 8+ and 6+ yrast states in ⁹⁴Ru were measured to posses half-lives of 64(1) µs and 63(4) ns respectively. These measurements are consistent with the published, highest-precision values for these nuclei. The data on ⁹⁴Pd provide the first measurement of the B(E2:8+ → 6+) for this N = 48 nucleus at 5.3(1)×10−3 e² b² for a half-life of 1.2(3) ns. The measured B(E2) value compare favourably with predictions from state-of-the-art shell model calculations using the Gross-Fenkel and JUN45 interactions assuming a closed 7638Sr38 core.