First high-resolution in-beam γ-ray spectroscopy of neutron-rich Mo isotopes at relativistic energy

Abstract

High-resolution in-beam $\gamma$-ray spectroscopy of the neutron-rich ${}^{110}$Mo${}_{68}$ and ${}^{112}$Mo${}_{70}$ isotopes was performed for the first time at relativistic energies. This experiment was conducted at the Radioactive Isotope Beam Factory (RIBF), RIKEN. The ${}^{110}$Mo and ${}^{112}$Mo isotopes were produced via nucleon removal reactions of radioactive Mo and Tc ions, and the $\gamma$ rays emitted following these reactions were measured using the High-resolution Cluster Array at RIBF (HiCARI). Doppler-corrected energy spectra enabled the precise determination of transition energies and half-lives through the line-shape method. In addition to providing new lifetime information, the level scheme of ${}^{112}$Mo was extended, including the $\gamma$-band structure, and the precision of existing level energies was significantly improved. Using the lifetime data, reduced transition probabilities were deduced. The $B(E2;2_1^{+}\to 0_1^{+})$ values indicate large collectivity and deformation, while the properties of the $2_2^{+}$ states and their decay to the ground-state band point to an increase in triaxial deformation from mid-shell toward $N=70$. To interpret these findings, two theoretical models were applied and compared with the experimental results highlighting the importance of triaxial deformation.