Muon-induced fission in 235U and 238U

Muon-induced prompt and delayed fission yields in 235U and 238U have been measured. A coincidence with the muonic uranium Kα X-rays was used to identify the muon stop in the target. The experimental absolute fission yields per muon stop were 0.142 ± 0.023 for 235U and 0.068 ± 0.013 for 238U. The disappearance rate of muons from the 1s state of muonic uranium has also been measured in the fission mode. Muon-induced fission lifetimes were 71.6 ± 0.6 ns for 235U and 77.2 ± 0.4 ns for 238U. No evidence for a short-lifetime fission – isomer component was found. Comparison of lifetime results with previously measured values in the electron, gamma, and neutron decay modes indicated that the systematic discrepancies could be explained by muon capture on fission fragments produced from prompt fission.