Half-lives of the extremely neutron-rich isotopes ${}_{}{}^{91-98}{}_{}{}^{}\mathrm{Rb}$, ${}_{}{}^{94-98}{}_{}{}^{}\mathrm{Sr}$, ${}_{}{}^{96-98}{}_{}{}^{}\mathrm{Y}$, ${}_{}{}^{142-146}{}_{}{}^{}\mathrm{Cs}$, ${}_{}{}^{143-148}{}_{}{}^{}\mathrm{Ba}$, ${}_{}{}^{144-149}{}_{}{}^{}\mathrm{La}$, and ${}_{}{}^{149}{}_{}{}^{}\mathrm{Ce}$ were determined. The isotopes ${}_{}{}^{147,148}{}_{}{}^{}\mathrm{Ba}$, and ${}_{}{}^{149}{}_{}{}^{}\mathrm{La}$ were identified for the first time and their half-lives measured. The values obtained, in seconds, are 0.72±0.07 for ${}_{}{}^{147}{}_{}{}^{}\mathrm{Ba}$, 0.47±0.20 for ${}_{}{}^{148}{}_{}{}^{}\mathrm{Ba}$ and 1.2±0.4 for ${}_{}{}^{149}{}_{}{}^{}\mathrm{La}$. The other measured half-lives either confirm or improve previous measurements. An extrapolation procedure based on the systematic behavior of experimental half-lives for the prediction of half-lives not yet measured was used. Similar systematic behavior is also apparent for half-lives predicted within the framework of the gross theory of $\beta$ decay.

RADIOACTIVITY ${}_{}{}^{91-98}{}_{}{}^{}\mathrm{Rb}$, ${}_{}{}^{94-98}{}_{}{}^{}\mathrm{Sr}$, ${}_{}{}^{96-98}{}_{}{}^{}\mathrm{Y}$, ${}_{}{}^{142-146}{}_{}{}^{}\mathrm{Cs}$, ${}_{}{}^{143-148}{}_{}{}^{}\mathrm{Ba}$, ${}_{}{}^{144-149}{}_{}{}^{}\mathrm{La}$, ${}_{}{}^{149}{}_{}{}^{}\mathrm{Ce}$ [from ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$ ($n$, fission)]; measured $T_{\frac{1}{2}}$. Si surface barrier detector. Mass-separated Rb, Sr, Cs, and Ba activities.

• Received 23 August 1978

DOI:https://doi.org/10.1103/PhysRevC.19.1948