A new precision measurement of the mass of ${}_{}{}^8{}_{}{}^{}\mathrm{He}$ has been performed by observing ${}_{}{}^8{}_{}{}^{}\mathrm{He}$ events from the reaction ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$(${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^8{}_{}{}^{}\mathrm{He}$)${}_{}{}^{60}{}_{}{}^{}\mathrm{Ni}$ at an incident beam energy of 80 MeV. The $Q$ values and mass excess are determined to be $Q=-31.796\mathrm{}\pm 0.008$ MeV and mass excess = 31.593 ± 0.008 MeV. The new ${}_{}{}^8{}_{}{}^{}\mathrm{He}$ mass allows for a more stringent test of the isobaric multiplet mass equation in the $A=8\mathrm{}$ quintet. A significant deviation from the quadratic mass equation persists.

NUCLEAR REACTIONS ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$(${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^8{}_{}{}^{}\mathrm{He}$). Measured reaction $Q$ value and mass excess. Deduced coefficients of IMME for the $A=8\mathrm{}$ isobaric quintet.

• Received 6 July 1977

DOI:https://doi.org/10.1103/PhysRevC.16.1835