The disappearance rate of muons from the $1s$ state of muonic actinide atoms has been measured by detecting muon-decay electrons. The experimental muon lifetimes are (79.2 ± 2.0), (75.4 ± 1.9), (73.5 ± 2.0), and (73.4 ± 2.8) nsec for muonic ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$, ${}_{}{}^{235,238}{}_{}{}^{}\mathrm{U}$, and ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$, respectively. The muon-capture rates deduced from the data are compared with the predictions of various theories. The experimental values are consistent with the systematics of muon-capture rates in the heavy elements but are generally higher than theoretical predictions, which take deformation of the nuclear charge distribution into account. The results provide no evidence for a muon-induced isomeric fission process.

RADIOACTIVITY Muonic atoms ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$, ${}_{}{}^{235,238}{}_{}{}^{}\mathrm{U}$, ${}_{}{}^{239}{}_{}{}^{}\mathrm{Pu}$; measured muon-disappearance rates, deduced total muon-capture rates, upper limit for population of shape-isomeric states.

• Received 13 December 1976

DOI:https://doi.org/10.1103/PhysRevC.15.2169