Actinide muonic atom lifetimes deduced from muon-induced fission

Abstract

Time distributions of fragments from delayed fission after muon capture have been measured for muonic $^{235}\mathrm{U}$, $^{238}\mathrm{U}$, $^{237}\mathrm{Np}$, $^{239}\mathrm{Pu}$, and $^{242}\mathrm{Pu}$. Comparison of these data with previously measured lifetimes using muon decay electrons, neutrons, and $\ensuremath{\gamma}$ rays emitted after muon capture indicates that the observed systematic discrepancies are due to atomic muon capture by fission fragments after prompt fission induced by radiationless muonic transitions. The deduced capture rates are compared with theoretical models, and very good agreement is found with a giant-resonance excitation model.RADIOACTIVITY Muonic atoms $^{235}\mathrm{U}$, $^{238}\mathrm{U}$, $^{237}\mathrm{Np}$, $^{239}\mathrm{Pu}$, and $^{242}\mathrm{Pu}$. Measured fission fragment time distributions, deduced total muon-capture rates and isotopic effect, present data compared to lifetimes based on all other decay channels.