Variational Approach to Medium Mass N=Z Nuclei

Abstract

The medium mass nuclei in the A≃ 70 mass region display a remarkable diversity of shapes and rapid changes in structure with particle number, angular momentum and excitation energy. During the last three years rapid experimental progress has been made and new data on medium mass even even N=Z nuclei are available. A distinct spherical-deformed shape coexistence was identified in the N=Z nucleus ⁵⁶Ni. The experimental results indicate the coexistence of an irregular sequence of yrast states and two deformed bands. Oblate deformed ground-and low-spin states are likely for N ≃ Z ≃ 36, and most of these nuclei are expected to display shape mixing. Also very elongated prolate ground state shapes are predicted for N ≃ Z ≃ 38, 40. Two distinct rotational bands were found in the N=Z nucleus ⁶⁸Se, the ground state band having properties consistent with collective oblate rotation, and the excited band having characteristics consistent with prolate deformation. In the nucleus ⁷²Kr the oblate and prolate configurations are expected to be close-lying, but so far only the yrast sequence has been identified. Preliminary results on ⁷⁶Sr and ⁸⁰Zr advanced the yrast sequence to intermediate spins. These nuclei are predicted to have very elongated prolate ground state shapes.