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Abstract |
Background: The nuclear structure in the region southwest of the doubly magic 208 208Pb is important to benchmark theoretical models relevant for neutron-rich heavy element formation and for the origin of the A approximate to 195 peak in the mass abundance distribution. Although neutron-rich Pb, Tl, and Hg (Z = 80-82) isotopes are relatively well studied, experimental data for neutron-rich Au isotopes (Z = 79) remain largely limited due to experimental challenges. Purpose: The purpose of this work is to investigate the evolution of the high-spin structure in neutron-rich Au isotopes near the N = 126 shell closure and to characterize the underlying shell-model configurations, with a particular focus on the roles of the high-j unique-parity pi pi h pi h11 pi h11/ pi h11/2 and v vi vi13 vi13/ vi13/2 orbitals. Methods: Neutron-rich 195-202Au isotopes were produced using multinucleon transfer reactions of 198 198Pt( 198Pt(136 198Pt(136Xe, x xI) y yAu at a beam energy of 7 MeV/nucleon. Prompt and delayed gamma-ray spectroscopy of isotopically identified reaction products was performed with a unique experimental setup combining the VAMOS + + large acceptance magnetic spectrometer, the AGATA high-purity germanium gamma-ray tracking array, and the CATLIFE detection system. Results: In even-A 196,198,200,202Au isotopes, prompt gamma-ray transitions built on the 12-isomer have been observed for the first time. The odd-J band built on the 11-state vanishes for A 196. In odd-A 195,197,199,201Au isotopes, new prompt and delayed gamma-ray transitions above the 11/2-isomer were identified, confirming and extending the known level schemes. New isomeric states assigned to (25/2+) have been established in 199 199Au and 201 201Au. The minima in the excitation energies of the bands as a function of N built on the 11/2-and 12-isomers occur at 198 198Au (N = 119), showing a dip against an otherwise smooth evolution. Conclusions: Large-scale shell-model calculations based on the Kuo-Herling hole effective interaction show an overall good agreement with experimental level schemes. However, the present calculations do not reproduce the minima in excitation energies at N = 119 observed in both Au and Hg isotopes. A systematic analysis of pi pi h pi h11 pi h11/ pi h11/2 and nu nu i nu i13 nu i13/ nu i13/2 hole occupancies, together with spin contributions of protons and neutrons, sheds light on the role of these high-j unique-parity orbitals in the generation of high-spin states. Part of the results of this work have been reported in another publication |
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