Quenching of the octupole rotational band in ⁷¹Ge

The main goal of this study was to enhance the knowledge of the properties of the known octupole rotational band in ⁷¹Ge, including transition rates, and to investigate whether the band persists to higher spin. An experiment at Florida State University using the ⁶²Ni(¹⁴C, αn) reaction at 50 MeV was used to produce ⁷¹Ge at high spin. An array of 10 Compton-suppressed Ge detectors, consisting of 3 Clover detectors and 7 single-crystal detectors, was used to measure the γ decays in coincidence. An analysis of the resulting coincidence spectra resulted in the placement of 13 additional transitions in the ⁷¹Ge level scheme, one of which (1092 keV) extends the octupole band to a (35/2^–)$ state at 8206 keV. However, calculations of the kinematic moment of inertia show that the 1092-keV transition disrupts the rigid rotational pattern and is likely associated with a band crossing, potentially quenching the octupole deformation. Transition strengths inferred from lifetime measurements in the octupole band are not well reproduced by either shell-model calculations using the JUN45 interaction or a semi-microscopic cluster model, while those for the νg_9/2 band are in good agreement with the corresponding shell-model predictions. Comparisons between the octupole band in ⁷¹Ge and negative-parity bands based on 3^– octupole states in some neighboring even-even nuclei show both similarities and differences. Systematic trends within the νg_9/2 bands among odd-A Ge isotopes point to increased collectivity near N = 40.