RADIATIVE MUON-CAPTURE ON AL, SI, CA, MO, SN, AND PB

The branching ratio for radiative muon capture (RMC), relative to the nonradiative process, is sensitive to g(p) the induced pseudoscalar coupling constant of the weak hadronic current. The photon energy spectra from RMC on Al-27, Si-28, Ca-40, (nat)Mo, (nat)Sn, and (nat)Pb have been measured using a high-acceptance pair spectrometer. The measured partial branching ratios, R(gamma), for photons of 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(-5). The results confirm the previously observed suppression of R(gamma) with increasing Z for Z > 20. For Ca-40 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 g(p), but the more recent calculation does not reproduce the data for any value of g(p).