Highly Proton-RichTz=−2Nuclides:C8andMg20

Abstract

Two nuclides with a proton excess of 4 have been produced via the ($\alpha ,{}_{}{}^8{}_{}{}^{}\mathrm{He}$) reaction, and their masses measured. The mass excess of ${}_6{}^8{}_{}{}^{}\mathrm{C}$ is 35.30 ± 0.20 MeV, and ${}_{}{}^8{}_{}{}^{}\mathrm{C}$ is therefore unbound with a measured width of ${220}_{-140\mathrm{}}^{+80\mathrm{}}$keV. The ${}_{}{}^8{}_{}{}^{}\mathrm{C}$ mass excess is 0.57 MeV less than the Kelson-Garvey prediction. For ${}_{12}{}^{20}{}_{}{}^{}\mathrm{Mg}$, a mass excess of 17.74 ± 0.21 MeV is found, indicating that ${}_{}{}^{20}{}_{}{}^{}\mathrm{Mg}$ is nucleon stable. Knowledge of the ${}_{}{}^{20}{}_{}{}^{}\mathrm{Mg}$ mass permits for the first time a test of the isobaric multiplet mass equation in an isobaric quintet, and good agreement is found.