Structural evolution in the neutron-rich nuclei 106Zr and 108Zr

Abstract

The low-lying states in 106 Zr and 108 Zr have been investigated by means of β-γ and isomer spectroscopy at the RI beam factory, respectively. A new isomer with a half-life of 620 ± 150 ns has been identified in 108 Zr. 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 sub-shell closure at N = 64. The deformed ground state of 108 Zr indicates that a spherical sub-shell gap predicted at N = 70 is not large enough to change the ground state of 108 Zr to the spherical shape. The possibility of a tetrahedral shape isomer in 108 Zr is also discussed.