The Study Of Neutron-Rich Isotopes Of Sr And Zr In A～100 Region

Recently, with the development of efficient large-scale y-detector arrays, such as Gammasphere and Eurogam, remarkable progress has been made in the investigation of nuclear structure in A-100 neutron-rich region. Experimentally, by measuring the prompt y rays of spontaneous fission or induced fission of heavy nuclei, much information about high spin states of neutron-rich isotopes in this region has been obtained. For neutron-rich A-100 nuclei, they lie far from theβstability, and the valence nucleons begin to fill the h11/2 neutron and g9/2 proton orbitals. The nuclear structure in this mass region is very sensitive to the occupancy level of these single-particle configurations, which is illustrated by the rapid changes in nuclear spectroscopic properties as a function of both neutron and proton numbers. One of the interesting features in this region is the shell-closure effects of the Z=40 and N=56 spherical subshells and a sudden onset of large ground-state deformation for Z≥60. In another aspect, phenomenon of nuclear structure in these nuclei can make them an ideal testing ground for various theoretical models.So, based on the advent of new research on this region above, we have studied the Sr, Zr axial symmetric isotopes by applying projected shell model approach in this paper. The energy bands of neutron-rich nuclei 98-102Sr,100-104Zr have been calculated, which have a good agreement with the experiment data. With the analysis on band-crossing phenomenon between ground-state band and quasi-particle rotational bands, the contribution to produce yrast band, the relation between kinematic moment of inertia and the square of the rotational frequency, we have obtained a lot of significant results as follows. First, the deformation of Sr, Zr nuclei in the low spin region depends entirely on the nature of the ground state band which in turn depends on 0-qp intrinsic state. In other words, the physical mechanism about deformation is mostly contained in the 0-qp intrinsic state. Second, with the spin increasing, the neutron pairs and proton pairs in the high-j intruder states near Fermi-level will break down. Then, the ground-state band will be crossed by the quasi-particle rotational bands. Accordingly, the kinematic moment of inertia will change to some extent. Meanwhile, through analyzing the intrinsic structure of positive and negative parity side bands, we found that the low-excitation deformation bands are attributed to the high-j intruder states 1g7/2 and 1h11/2 in the N=4,5 harmonic-oscillator shells. In particular, with the discussion of quasi-particle rotational bands, it is clear that the quasi-particles in the orbit v5/2"[532], v3/2+[411] and v3/2+[413] play an important role in the deformation of neutron-rich Sr, Zr axially symmetric nucleus. In addition, the occurrence of low energy and high-K bands can provide some references for us to study the nuclear isomer.