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The investigation of the beta decay of 46K: Detailed spectroscopy of the low-lying structure of 46Ca with the GRIFFIN Spectrometer

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Thesis type
(Dissertation) Ph.D.
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The calcium region is currently a new frontier for modern shell model calculations, and detailed experimental data from these nuclei is critical for a comprehensive understanding of the region.Due to its very low natural abundance of 0.004%, the structure of the magic nucleus 46Ca has not been studied in great detail. Some excited states were previously identified by various reaction mechanisms, and few gamma rays were placed in the level scheme from results of beta-decay experiments equipped with limited detection capabilities. A high-statistics data set of the beta decay of the 46K 2- ground state into the excited states of 46Ca was measured with the GRIFFIN spectrometer located at TRIUMF-ISAC in December of 2014. A radioactive beam consisting almost entirely of 46K was implanted at the center of the GRIFFIN array, and the emitted gamma rays were detected by 15 high-purity germanium clover detectors. From forty hours of data collection, 430 million gamma-gamma coincidences were observed and analysed to construct the 46Ca level scheme. In total, 194 gamma rays were identified and placed into the level scheme; 150 of these transitions were observed for the first time. Angular correlations between pairs of gamma rays were analysed to investigate the spin assignments of the observed excited states. Correlations were investigated for 18 of the 42 observed excited states, and it was possible to confirm 7 previously reported spin assignments, and assign 3 new spins of 3-, 2-, and 3- for the 4435, 5052, and 5535 keV states, respectively. The measured half-life of the 96.41(10) s is in agreement with previous results. From the observed beta feeding intensities of this work, it is suggested that the 46K 2- ground state may contain more proton s1/2 character than has been previously believed. This is due to the strong population of the 5052 keV 2$^-$ state and the absence of observed feeding to the 46Ca ground state.
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Thesis advisor: Andreoiu, Corina
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