Zdependence of theN=152deformed shell gap: In-beam γ-ray spectroscopy of neutron-richPu245,246

Abstract

We have measured in-beam \ensuremath{\gamma} rays in the neutron-rich ${}^{246}{\mathrm{Pu}}_{152}$ and ${}^{245}{\mathrm{Pu}}_{151}$ nuclei by means of $^{244}\mathrm{Pu}$($^{18}\mathrm{O}$, $^{16}\mathrm{O}$)$^{246}\mathrm{Pu}$ and $^{244}\mathrm{Pu}$($^{18}\mathrm{O}$, $^{17}\mathrm{O}$)$^{245}\mathrm{Pu}$ neutron transfer reactions, respectively. The \ensuremath{\gamma} rays emitted from $^{246}\mathrm{Pu}$ ($^{245}\mathrm{Pu}$) were identified by selecting the kinetic energy of scattered $^{16}\mathrm{O}$ ($^{17}\mathrm{O}$) detected by Si $\ensuremath{\Delta}E\ensuremath{-}E$ detectors. The ground-state band of $^{246}\mathrm{Pu}$ was established up to the ${12}^{+}$ state. We have found that the shell gap of $N=152$ is reduced in energy with decreasing atomic number by extending the systematics of the one-quasiparticle energies in $N=151$ nuclei into those in $^{245}\mathrm{Pu}$. This reduction of the shell gap clearly affects the ${2}^{+}$ energy of the ground-state band of $^{246}\mathrm{Pu}$.