Investigation of octupole collectivity near the I=72 shape-transitional point

Enhanced octupole collectivity is expected in the neutron-deficient Ge, Se, and Kr isotopes with neutron number N approximate to 40 and has indeed been observed for 70,72Ge. Shape coexistence and configuration mixing are, however, a notorious challenge for theoretical models trying to reliably predict octupole collectivity in this mass region, which is known to feature rapid shape changes with changing nucleon number and spin of the system. To further investigate the microscopic configurations causing the prolate-oblate-triaxial shape transition at A approximate to 72 and their influence on octupole collectivity, the rare isotopes 72Se and 74,76Kr were studied via inelastic proton scattering in inverse kinematics. While significantly enhanced octupole strength of approximate to 32 Weisskopf units (W.u.) was observed for 72Se, only strengths of approximate to 15 W.u. were observed for 74,76Kr. In combination with existing data, the new data clearly question a simple origin of enhanced octupole strengths around N = 40. The present work establishes two regions of distinct octupole strengths with a sudden strength increase near the A = 72 shape-transitional point.

Automated summary

Enhanced octupole collectivity is observed in the neutron-deficient Ge, Se, and Kr isotopes. However, theoretical models struggle to predict octupole collectivity accurately due to shape coexistence and configuration mixing. In this study, the rare isotopes 72Se and 74,76Kr were investigated, revealing two distinct regions of octupole strengths near the shape-transitional point at A=72.