Ra218αReduced Width and Its Consequences forαClustering in the Heavy Elements

Abstract

Nuclei of ${}_{}{}^{218}{}_{}{}^{}\mathrm{Ra}$ were produced in the reaction ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}({}_{}{}^{13}{}_{}{}^{}\mathrm{C},3n)$. After being separated from the beam by a velocity filter, they were implanted in a Si(Au) surface-barrier detector and their $\alpha$-particle decays were observed in the same detector. From these $\alpha$-decay events the half-life of ${}_{}{}^{218}{}_{}{}^{}\mathrm{Ra}$ was measured to be 25.6 ± 1.1 μs, almost a factor of 2 greater than the previously reported value of 14 ± 2 μs. The resultant $\alpha$ width fits well into the overall picture of $\alpha$-decay-rate systematics and weakens one piece of evidence quoted for the existence of $\alpha$ clusters in heavy elements.