丰中子A~100质量区内的扁椭球高K同核异能态

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

远离核素图上“稳定谷”的丰中子核一直是核物理学研究的热点。作为形变丰中子核的一种特殊的亚稳定激发态,高K同核异能态的形状大多数为长椭球,扁椭球的高K同核异能态非常少见。近期的一项实验认为丰中子核^(94)Se上的K_(n)=7^(-)两准粒子态为扁椭球。这是形变原子核上存在扁椭球高K同核异能态的第一个实验证据。结合相关实验,我们猜测可能有其它尚未发现的扁椭球高K同核异能态存在于丰中子A~100质量区。利用组态限制势能面计算方法,本文对丰中子A~100质量区内的K_(n)=9^(-)和K_(n)=7^(-)两准粒子态进行了研究,并预言了此质量区内扁椭球高K同核异能态的可能位置。根据Nilsson模型,扁椭球高K同核异能态的存在与费米能级附近的高Ω单粒子轨道有关。这些高Ω单粒子轨道来源于高j闯入态在扁椭球形变时的退简并。扁椭球高K同核异能态是研究丰中子核形变参数、激发能等物理性质的理想对象,有助于加深我们对于形变原子核能级结构的理解。

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_(n)=7^(-)two-quasiparticle state of neutron-rich^(94)Se 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_(n)=9^(-)and K_(n)=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-Ωsingle particle orbitals around the Fermi level.These high-Ωsingle 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.