Oblate High-K Isomers in the Neutron-rich A~100 Region

Neutron-rich nuclei which are far away from the “ valley of stability ” on the chart of nuclides have always been a hotspot of nuclear physics. As a special kind of metastable excited states of deformed neutron-rich nuclei, high-K isomers usually are prolate, while oblate high-K isomers are rare. A recent experiment suggested that the K^\mathrm\pi =7^- two-quasiparticle state of neutron-rich ⁹⁴Se is oblate. This is the first experimental evidence that oblate high-K isomers exist in deformed nuclei. In combination with relevant experiments, we made an assumption that there are other unobserved oblate high-K isomers in the neutron-rich A~100 region. Theoretical investigations of K^\mathrm\pi =9^- and K^\mathrm\pi =7^- two-quasiparticle states in the neutron-rich A~100 region have been performed with the configuration-constrained potential energy calculation method, possible positions of oblate high-K isomers in this region have been predicted. According to Nilsson model, the existence of oblate high-K isomers relies on high-Ω single particle orbitals around the Fermi level. These high-Ω single particle orbitals origin from the breaking of degeneracy of high-j intruder states when the nuclei are oblate. Oblate high-K isomers are ideal subjects for the research of deformation parameters and excited energies of neutron-rich nuclei, and contribute to a better understanding of energy level structures of deformed nuclei.