Ordinary muon capture rates on ${}^{100}$Mo and ${}^{\mathrm{nat}}$Mo for astro-antineutrinos and double beta decays

Abstract

\item[Background] The nuclear responses for antineutrinos associated with double beta decays (DBDs) and astro-antineutrino interactions are studied by measuring ordinary muon capture (OMC) rates. \item[Purpose]The experimental studies of absolute OMC rates and their mass number dependence for ${}^{100}$Mo and the natural Mo are currently of interest in astro-antineutrinos and DBDs. \item[Method]The OMC rates were obtained experimentally by measuring the time spectrum of the trapped muon's decay into electrons to obtain the half-lives of the trapped muons. \item[Results]The OMC rate for the enriched isotope of ${}^{100}$Mo is $\hat{I}›$(${}^{100}$Mo)=(7.07$\pm$0.32)$\times 10^6$ s${}^{-1}$, while that for the natural Mo is $\hat{I}›$(${}^{\mathrm{nat}}$Mo)=(9.66$\pm$0.44)$\times 10^6$ s${}^{-1}$, i.e., $\hat{I}›$(${}^{100}$Mo) is about 27$\%$ of $\hat{I}›$(${}^{\mathrm{nat}}$Mo), reflecting the blocking effect of the excess neutrons for the proton-to-neutron transformation in OMC. The present experimental observation is consistent with the predictions using Goulard-Primakoff's (GPs) and Primakoff's (Ps) empirical equations. \item[Conclusions] The absolute OMC rates for ${}^{100}$Mo and ${}^{\mathrm{nat}}$Mo were measured. The large neutron excess in ${}^{100}$Mo gives a much lower OMC rate than ${}^{\mathrm{nat}}$Mo. On both ${}^{100}$Mo and ${}^{\mathrm{nat}}$Mo, consistent OMC rates with the GP and P values are observed.

5 pages, 3 figures, 2 tables