Neutron Emission Following Muon Capture inCe142,Ce140,Ba138, andSn120

Branching ratios to excited nuclear states formed after muon capture have been measured with Ge(Li) detectors. The delayed $\gamma$ rays were observed in studies of muonic ${}_{}{}^{142}{}_{}{}^{}\mathrm{Ce}$, ${}_{}{}^{140}{}_{}{}^{}\mathrm{Ce}$, ${}_{}{}^{138}{}_{}{}^{}\mathrm{Ba}$, and ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$, using separated isotopes. The resulting isotopes formed indicate at least a 60% probability of neutron emission upon muon capture, with the most likely product resulting from single-neutron emission. No evidence for delayed proton emission with a probability higher than 2% was found. Using our more precise energies for the observed nuclear transitions, we present revised energy levels schemes for ${}_{}{}^{141}{}_{}{}^{}\mathrm{La}$, ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$, ${}_{}{}^{137}{}_{}{}^{}\mathrm{Cs}$, and ${}_{}{}^{119}{}_{}{}^{}\mathrm{In}$.