The branching ratio for radiative muon capture (RMC), relative to the nonradiative process, is sensitive to ${\mathit{g}}_{\mathit{p}}$, the induced pseudoscalar coupling constant of the weak hadronic current. The photon energy spectra from RMC on ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Mo}$, ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Sn}$, and ${}_{}{}^{\mathrm{nat}}{}_{}{}^{}\mathrm{Pb}$ have been measured using a high-acceptance pair spectrometer. The measured partial branching ratios, ${\mathit{R}}_{\gamma }$, for photons of ${\mathit{E}}_{\gamma }$>57 MeV are 1.43±0.13, 1.93±0.18, 2.09±0.19, 1.11±0.11, 0.98±0.09, and 0.60±0.07 respectively, in units of ${10}^{\mathrm{-}5}$. The results confirm the previously observed suppression of ${\mathit{R}}_{\gamma }$ with increasing Z for Z>20. For ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ the present result is in good agreement with previous measurements. For the heavier nuclei, the results are compared with two recent calculations performed in the Fermi-gas model. In one case the data indicate a complete quenching of ${\mathit{g}}_{\mathit{p}}$, but the more recent calculation does not reproduce the data for any value of ${\mathit{g}}_{\mathit{p}}$.

• Received 5 May 1992

DOI:https://doi.org/10.1103/PhysRevC.46.1094