Spectroscopy of neutron-rich germanium and krypton isotopes - A quest of triaxiality

This work covers the spectroscopic analysis of 84,86,88Ge and 94,96Kr isotopes populated by different reactions within the SEASTAR campaign 2015. The experimental setup and the data analysis are described in detail. This analysis includes necessary functionality checks and calibrations of the detectors along the beam line. In-flight γ-ray spectroscopy of 84,86,88Ge was performed after various knock-out reactions. γ-spectroscopy of neutron-rich 88Ge was performed for the first time. The Doppler-corrected γ-ray spectra are analyzed with simulated lineshapes of occurring transitions. In total 16 transitions are observed ten of which so far unknown. New level schemes for 86,88 Ge are proposed based on the observed transition intensities and systematics of neighboring Ge isotopes. The obtained level schemes are compared to state-of-the-art theoretical calculations. The assignment of a 3⁺ state of 86Ge agrees with new shell model and SCCM predictions. The agreement to the level orderings from the collective model by Davydov and co-workers points to an amount of rigid triaxiality in 86Ge. This is the first indication of rigid triaxiality in an unstable, neutron-rich nucleus. In addition, an analysis of reaction cross sections, as well as cross sections for the excitation of a particular state is performed. This data set represents one of the first results for this newly-accessible region of the nuclear chart. Furthermore, 84,86Ge and 94,96Kr are investigated after (p,p') reactions, which excite different states than the knock-out reactions. These states are candidates for octupole 3⁻ states, which are the first benchmark for the octupole degree of freedom in this exotic region. The obtained (p,p') cross sections of the 2⁺₁ states from 94,96Kr are compared to the transition strength known from literature based on the deformation length