Structure of theN=59 nucleus97Sr: coexistence of spherical and deformed states

A band with a rotational pattern based on a state at 585.1 keV has been identified in theN=59 neutron-rich nucleus⁹⁷Sr. Its properties lead to the 422] 3/2 Nilsson-orbital assignment for the band head. There is evidence for a second band with the head at 644.7 keV and the configuration 541] 3/2. Since the ground state and the lowest excited levels are spherical, shape coexistence is established for⁹⁷Sr. A deformed nature of several levels at 500–600 keV results also from QRPA-model calculations. The structure of the low-lying spherical levels has been studied in the frame of the IBF model. The results of the present investigations lead to a better understanding of theN=59 isotones which constitute the link between the spherical and deformed nuclei atA～100 as a species with shape coexistence but without any indications of particular softness.