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Exotic Nuclei with the Fragment Mass Analyzer

其他書名	The Mass of 68Se, the Yrast Structure of the Near-drip Line Nuclei 1761̓78Hg and 177Au
出版	Vanderbilt University, 2000
URL	http://books.google.com.hk/books?id=Z4Z0NwAACAAJ&hl=&source=gbs_api

註釋The work described in this thesis deals with two of the many applications of the Fragment Mass Analyzer, a recoil mass spectrometer installed at the ATLAS facility at Argonne National Laboratory. The rapid-proton capture (rp- ) process has been recognized as a key contributor to the nucleosynthesis of heavy elements in massive stars. Understanding the production rate of each element is a chain of nuclei requires knowledge of each participant's half-life and mass. 68Se is involved in the rp-process as a so-called waiting point. This work determined its half-life to be 38.8 +- 2.6 seconds and its [beta]+ decay scheme was also delineated. Furthermore, the mass of 68Se was measured for the first time. The experimental value for the mass excess, [delta] = -54.3 +- 0.5 MeV, compares favorably with the latest theoretical prediction of [delta] = -54.15 MeV. The low spin yrast bands of 176,178Hg and 177Au were observed for the first time using the AYEBall array in conjunction with the recoil-decay tagging technique (RDT). The light even-even Hg isotopes are known to exhibit shape coexistence between a level structure associated with an oblate ground state ([beta]2 ~ -0.15) and a rotational band built on a deformed prolate ([beta]2 ~ 0.25) shape. In this study, the excitation energy of the prolate rotational band was found to increase with decreasing mass between mid-shell (N = 102) and N = 98 (178Hg) to the point where there is no longer evidence for its presence at low spin (I 6,) in 176Hg. The data are in qualitative agreement with mean field calculations. Comparison of the yrast band of 177Au with similar bands in the neighboring isotones 176Pt and 178Hg indicates that the odd-proton contributes little to the shape-driving effects observed in the light even-even Hg isotopes.