Coupling a proton and a neutron to the semidoubly magic nucleusNi68: A study ofCu70via theβdecay ofNi70andCu70

Abstract

The $^{70}\mathrm{Ni}$ nucleus has been produced at the LISOL facility and its $\ensuremath{\beta}$ decay to $^{70}\mathrm{Cu}$ has been observed. In parallel, the $^{70}\mathrm{Cu}$ nucleus has been produced at the ISOLDE facility. A new third $\ensuremath{\beta}$-decaying isomeric state in $^{70}\mathrm{Cu}$ has been identified, partly with the aid of the in-source laser spectroscopy method. Its measured half-life is ${T}_{1∕2}=33(2)\phantom{\rule{0.3em}{0ex}}\mathrm{s}$. In addition, two isomeric transitions in $^{70}\mathrm{Cu}$ have been observed at energies of 101.1(3) and $141.3(3)\phantom{\rule{0.3em}{0ex}}\text{keV}$, and it allowed the relative placement of the three $^{70}\mathrm{Cu}$ isomeric states and their tentative spin and parity assignments. The new $^{70}\mathrm{Cu}$ isomer was found to be weakly populated in the $\ensuremath{\beta}$ decay of $^{70}\mathrm{Ni}$. It allowed the construction of the $^{70}\mathrm{Ni}$ decay scheme. Furthermore, the $\ensuremath{\beta}$ decay of the three $^{70}\mathrm{Cu}$ isomers to $^{70}\mathrm{Zn}$ has been measured and their decay schemes are presented. The $^{70}\mathrm{Ni}$ $\ensuremath{\beta}$ decay to the isomeric states in $^{70}\mathrm{Cu}$ and their subsequent isomeric decay and $\ensuremath{\beta}$ decay to $^{70}\mathrm{Zn}$ are discussed within the extreme shell-model picture of two valence nucleons outside the semidouble magic $_{28}^{68}\mathrm{Ni}_{40}$ core and it yields satisfactory results. Large-basis shell-model calculations using $_{28}^{56}\mathrm{Ni}_{28}$ as the core and a realistic effective interaction support rather well the suggested interpretation.