Measurements of ordinary muon capture rates on 100Mo and natural Mo for astro-antineutrinos and double-β decays

Abstract

Ordinary muon capture (OMC) rates are valuable for studying the neutrino nuclear responses of astrophysical antineutrinos and double-β decays (DBDs). Currently, there is interest in experimental studies of the OMC rates and their mass number (A) dependence for Mo100 and natural Mo. To obtain these rates, a negative muon beam from the MuSIC facility at the Research Center for Nuclear Physics (RCNP), Osaka University was utilized. The half-lives of trapped muons were measured by using a muon stopping signal from a scintillation counter and the time distribution of the OMC nuclear gamma rays and the muon-decay electrons by Ge detectors. The present measurements yielded OMC rates for enriched and natural molybdenum of Λ(Mo100)=(7.07±0.32)×106s-1 and Λ(Monat)=(9.66±0.44)×106s-1, respectively. The observed OMC rate for Mo100 is approximately 27% smaller than that for natural Mo due to the blocking effect of the excess neutrons on the proton-to-neutron transformation in OMC. The present experimental observation is consistent with the Goulard-Primakoff (GP) and Primakoff (P) empirical equations. The impacts of the present results on the astro-antineutrinos and double-β decays are discussed.