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

TL;DR

This study investigates the low-lying states of neutron-rich 106Zr and 108Zr, revealing a new isomer, shape evolution, and questioning the predicted spherical sub-shell closure at N=70.

Contribution

It provides new experimental data on isomerism and shape evolution in 106Zr and 108Zr, challenging existing shell closure predictions.

Findings

Discovery of a 620 ns isomer in 108Zr.

Evidence of a deformed ground state in 108Zr.

Discussion of possible tetrahedral shape isomer.

Abstract

The low-lying states in 106Zr and 108Zr have been investigated by means of {\beta}-{\gamma} and isomer spectroscopy at the RI beam factory, respectively. A new isomer with a half-life of 620\pm150 ns has been identified in 108Zr. 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 108Zr indicates that a spherical sub-shell gap predicted at N = 70 is not large enough to change the ground state of 108Zr to the spherical shape. The possibility of a tetrahedral shape isomer in 108Zr is also discussed.