Isospin quintets in the1pands−dshells

The pion double-charge exchange reaction (${\pi }^{+}, {\pi }^{-}$) has been used to measure the ground-state masses of ${}_{}{}^{12}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{Ne}$, ${}_{}{}^{24}{}_{}{}^{}\mathrm{Si}$, and ${}_{}{}^{32}{}_{}{}^{}\mathrm{Ar}$. The mass excesses were found to be 32.059(48), 24.051(45), 10.682(52), and - 2.181(50) MeV, respectively. These are the first reported measurements of the masses of ${}_{}{}^{24}{}_{}{}^{}\mathrm{Si}$ and ${}_{}{}^{32}{}_{}{}^{}\mathrm{Ar}$ and the values for ${}_{}{}^{12}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{16}{}_{}{}^{}\mathrm{Ne}$ are improved over previous results. Good agreement with the isobaric multiplet mass equation $M=a+b{T}_z+c{T_z}^2$ is obtained for the known members of all four quintets.