High-spin spectroscopy and shell-model interpretation of the N < 126 radium isotopes $^{212}$Ra and $^{213}$Ra

Abstract

The level structures of $^{212}$Ra and $^{213}$Ra have been established via time-correlated $\gamma$-ray spectroscopy following the $^{204}$Pb($^{12}$C,4$n$)$^{212}$Ra and $^{204}$Pb($^{13}$C,4$n$)$^{213}$Ra reactions. In $^{212}$Ra, levels up to $\sim 6.2$ MeV were identified and firm spin-parity assignments were achieved to a $J^{\pi} = 19^+$ isomer with a mean life of 31(3) ns. For $^{213}$Ra the corresponding values were $\sim 4.5$ MeV in excitation energy and $J^{\pi} = 33/2^+$. Two isomeric states with $J^\pi = 23/2^+$, $\tau = 27(3)$ ns and $J^\pi = 33/2^+$, $\tau = 50(3)$ ns were discovered in $^{213}$Ra. The experimental data were compared with semiempirical shell-model calculations, which allowed dominant configurations to be assigned to most of the observed levels.