The masses of ${}_{}{}^{76}{}_{}{}^{}\mathrm{Kr}$ and ${}_{}{}^{74}{}_{}{}^{}\mathrm{Kr}$ were measured utilizing the ${}_{}{}^{78}{}_{}{}^{}\mathrm{Kr}$(${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^6{}_{}{}^{}\mathrm{He}$) and ${}_{}{}^{78}{}_{}{}^{}\mathrm{Kr}$(${}_{}{}^4{}_{}{}^{}\mathrm{He}$, ${}_{}{}^8{}_{}{}^{}\mathrm{He}$) reactions. Mass excesses of -68971±13 and -62210±75 keV were obtained for ${}_{}{}^{76}{}_{}{}^{}\mathrm{Kr}$ and ${}_{}{}^{74}{}_{}{}^{}\mathrm{Kr}$, respectively, and found to compare favorably with some mass formulae predictions, but not with others. Speculations about shape differences in light krypton and rubidium isotopes are presented as they relate to various mass formulae.

NUCLEAR REACTIONS ${}_{}{}^4{}_{}{}^{}\mathrm{He}$+${}_{}{}^{78}{}_{}{}^{}\mathrm{Kr}$, $E_{\mathrm{lab}}=79.7\mathrm{} \mathrm{and} 102.7$ MeV; measured $E_{6_{\mathrm{He}}}$, $E_{8_{\mathrm{He}}}$; ${}_{}{}^{76}{}_{}{}^{}\mathrm{Kr}$, ${}_{}{}^{74}{}_{}{}^{}\mathrm{Kr}$ deduced $Q$, masses; magnetic spectrograph. Enriched gas targets.

• Received 25 June 1982

DOI:https://doi.org/10.1103/PhysRevC.26.1914