Medium-spin structure of 96,97Sr and 98,99Zr nuclei and the onset of deformation in the A∼100 region Original Research Article

The N=58, 59 nuclei 96,97Sr and 98,99Zr produced in the spontaneous fission of 248Cm were studied using the EUROGAM2 array. Regular rotational bands have been found in 97Sr and 99Zr, firmly establishing shape coexistence in both nuclei. Contrary to earlier suggestions, no rotational bands were found on top of 0View the MathML source states in the N=58 nuclei 96Sr and 98Zr. It is likely, however, that the N=58 nuclei undergo a shape change along the yrast line from spherical ground state to weakly deformed medium-spin states. Numerous single-particle excitations of negative parity, observed in 97Sr and 99[loc=pre]Zr, suggest the important role of the View the MathML source shell in creating deformation in these nuclei. Quadrupole moments were determined for rotational bands in the N=58, 59, 60, 62 and 64 Sr and Zr nuclei. Deformation parameters, which increase gradually from View the MathML source at N=56, through View the MathML source at N=58 to View the MathML source at N=64, suggest that in strontium and zirconium isotopes the shape change happens gradually between N=56 and N=62, and is most likely due to an occupancy of three or more deformation-driving orbitals of View the MathML source parentage.