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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

  • 摘要: 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94Se上的 K^\mathrm\pi =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^\mathrm\pi =9^- K^\mathrm\pi =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。

     

    Abstract: 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.

     

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