The study of nuclear charge dispersion in the light-fission-product region from thermal-neutron irradiation of ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$ was begun with measurements on mass chain 77. An ion exchange procedure was developed which rapidly separated Ga from its daughter products, Ge and As. Ga separations were made at various times after fission, and the Ge daughter activities were isolated and measured. From these activities ${}_{}{}^{77}{}_{}{}^{}\mathrm{Ga}$ and ${}_{}{}^{78}{}_{}{}^{}\mathrm{Ga}$ were indirectly identified as fission products. The half-life of ${}_{}{}^{77}{}_{}{}^{}\mathrm{Ga}$ was determined to be 17.1±1.5 sec, and that of ${}_{}{}^{78}{}_{}{}^{}\mathrm{Ga}$ was estimated to be about 4 sec. The branching ratio of ${}_{}{}^{77}{}_{}{}^{}\mathrm{Ga}$ for formation of ${}_{}{}^{77m}{}_{}{}^{}\mathrm{Ge}$ and ${}_{}{}^{77g}{}_{}{}^{}\mathrm{Ge}$ was obtained from measurements of the 39-h ${}_{}{}^{77}{}_{}{}^{}\mathrm{As}$ activity at the time when the 54-sec ${}_{}{}^{77m}{}_{}{}^{}\mathrm{Ge}$ and the 11.3-h ${}_{}{}^{77g}{}_{}{}^{}\mathrm{Ge}$ had each mostly decayed. Values obtained for decay to ${}_{}{}^{77m}{}_{}{}^{}\mathrm{Ge}$ and ${}_{}{}^{77g}{}_{}{}^{}\mathrm{Ge}$ are 0.88±0.02 and 0.12±0.02, respectively. The fractional cumulative yield of ${}_{}{}^{77}{}_{}{}^{}\mathrm{Ga}$ was determined as 0.573±0.014.

• Received 25 March 1968

DOI:https://doi.org/10.1103/PhysRev.172.1262