The $\alpha$-decay property of ${}_{}{}^{215}{}_{}{}^{}\mathrm{Fr}$ has been studied by the pulsed-beam method, in which ${}_{}{}^{215}{}_{}{}^{}\mathrm{Fr}$ was produced in the ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}({}_{}{}^{12}{}_{}{}^{}\mathrm{C},\alpha 2n)$ reaction and its $\alpha$ decay was measured between natural beam bursts of the cyclotron. The ground state of ${}_{}{}^{215}{}_{}{}^{}\mathrm{Fr}$ was found to decay with $E_{\alpha }=9.355\mathrm{}\pm 0.010$ MeV and $t_{\frac{1}{2}}=0.12\mathrm{}\pm 0.02$ μsec. The reduced $\alpha$ width of ${}_{}{}^{215}{}_{}{}^{}\mathrm{Fr}$ is shown to fit the systematical trend of $N=128\mathrm{}$ isotones very well and to agree with the simple shell-model calculation. Distributions of recoil angles for reaction products in the (${}_{}{}^{12}{}_{}{}^{}\mathrm{C},\alpha \mathrm{xn}$) reaction were found to be quite different from those for (${}_{}{}^{12}{}_{}{}^{}\mathrm{C},xn$) products, giving a convenient method of distinguishing these reaction products.

[NUCLEAR REACTIONS ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}({}_{}{}^{12}{}_{}{}^{}\mathrm{C},xn)$, ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}({}_{}{}^{12}{}_{}{}^{}\mathrm{C},\alpha xn)$, $E=73-80\mathrm{}$ MeV; measured $\alpha$ decay and $W\left(\theta \right)$ of reaction products, $E_{\alpha }$, $t_{\frac{1}{2}}$; deduced $\alpha$-decay width of ${}_{}{}^{215}{}_{}{}^{}\mathrm{Fr}$.]

• Received 1 October 1973

DOI:https://doi.org/10.1103/PhysRevC.9.1168