Structural Evolution in the Neutron-Rich Nuclei Zr-106 and Zr-108
ABSTRACT The low-lying states in Zr-106 and Zr-108 have been investigated by means of beta-gamma and isomer spectroscopy at the radioactive isotope beam factory (RIBF), respectively. A new isomer with a half-life of 620 +/- 150 ns has been identified in Zr-108. For the sequence of even-even Zr isotopes, the excitation energies of the first 2(+) states reach a minimum at N = 64 and gradually increase as the neutron number increases up to N = 68, suggesting a deformed subshell closure at N = 64. The deformed ground state of Zr-108 indicates that a spherical subshell gap predicted at N = 70 is not large enough to change the ground state of Zr-108 to the spherical shape. The possibility of a tetrahedral shape isomer in Zr-108 is also discussed.