High-spin shape isomers and the nuclear Jahn-Teller effect
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High-spin isomers were systematically studied in N = 83 isotones. These isomers are of stretch coupled configurations and have oblate shapes. High-spin isomers can be categorized to be high-spin shape isomer, as they are caused by the sudden shape change from near spherical to an oblate shape. These isomers are considered to be a good example of the nuclear Jahn-Teller effect. By the systematic study of high-spin isomers, several results were obtained, such as (1) change of Z = 64 sub-shell gap energy and (2) experimental pairing gap energy at high-spin states. The Z = 64 sub-shell gap energy was found to decrease from 2.4 to 1.9 MeV as the proton number decreases from 64 to 60. Paring gap energies of high-spin states were experimentally extracted by the three-point expression using binding energies and excitation energies of high-spin isomers. These pairing gap energies at high-spin states are as large as those of the ground states, even though isomers have oblate shapes( β ∼ - 0.19).