High Spin Shape Isomers in N=83 Isotones

摘要

High-spin isomers in N=83 isotones have been systematically studied. Their spin-parities are 49/2~+ and 27~+ for odd and odd-odd nuclei, respectively. Life times of these isomers range between ～10ns and ～μs. High-spin isomers have stretch coupled configurations resulting from the breaking of a neutron magic 82 core, such as [v(f_(7/2)h_(9/2)i_(13/2)) πh_(11/2)~2]_(49/2)~+ for odd nuclei and [v(f_(7/2)h_(9/2)i_(13/2)) π(d_(5/2)~(-1)h_(11/2)~2)]_(27)~+ for odd-odd nuclei. These high-spin isomers have oblate shape. Experimental results were compared with those calculated by a deformed independent particle model (DIPM). Excitation energies of high-spin isomers in N=83 isotones with 60 ≤ Z ≤ 66 are almost constant. This constancy can be caused by a decrease of the sub-shell gap energy of Z=64 from 2.4 to 1.9MeV, as a proton number decreases from Z=64 to 60. These isomers are considered to be high-spin shape isomers stemmed from a sudden shape change from near spherical to an oblate shape. Searches for high-spin isomers in N=51 isotones with the same isomerism appeared in N=83 isotones have been started. For the first time, high-spin isomer was found in ~(93)Mo with the life time of 1.1μs. This isomer is expected to have the stretch coupled configuration of [v (d_(5/2)g_(7/2)h_(11/2)) πg_(9/2)~2]_(39/2)~-and have oblate shape. In order to search for high-spin isomers in N=51 isotones with Z < 40, an unstable nuclear beam ~(17)N was developed. Experiment will be carried out by the γ-ray spectroscopy method using secondary fusion reaction.