Study of Even-Even/Odd-Even/Odd-Odd Nuclei in Zn-Ga-Ge in the Proton-Neutron IBM/IBFM/IBFFM

The nuclei in the region with mass 60 ≤ A ≤ 70 are known to show the symmetry characters ranging from the U(5) to the 0(6) limits of IBM [1], and, in particular, it was recently pointed out that some nuclei have the critical E(5) symmetry [2]. We study a series of nuclei Zn-Ga-Ge in the proton-neutron IBM and the models derived from it: IBM2, IBFM2, IBFFM2. The nucleus 68Ga is described as a system with boson core of 66Zn plus a proton and a neutron. The neighboring nuclei 67Ga and 67Zn can be treated as systems with the same core with an odd proton and an odd neutron, respectively. Figure 1 shows tentative results of the energy levels. We also calculate electromagnetic properties as well as β+-decay rates among 68Ge, 68Ga and 68Zn. Although these nuclei have been studied in the IBM models with identical bosons [3], the IBM2 description will be important in explaining higher levels and β-decay where difference between proton and neutron bosons must be properly taken into account. Discussion will be given in connection with dynamical symmetries. Detailed analysis is being carried out.(author)