ISOTOPE DEPENDENCE OF RADIATIVE MUON-CAPTURE ON THE NI-58,NI-60,NI-62ISOTOPES

We report measurements of the photon rates and energy spectra from inc lusive radiative muon capture on three nickel isotopes using a photon pair spectrometer at the TRIUMF cyclotron. The Values of R-gamma, the partial branching ratios of radiative muon capture for photon energies >57 MeV, for Ni-58.60,Ni-62 were found to be (in units of 10(-5)) 1.4 8 +/- 0.08, 1.39 +/- 0.09, and 1.05 +/- 0.06, assuming a Fermi-gas pho ton spectral shape. The results reveal a significant isotope effect in the nickel branching ratios and a simple empirical scaling of the pre sent nickel and earlier nuclear R-gamma data with neutron excess. Furt hermore, the observed atomic mass and neutron excess dependence of the entire nuclear R-y data set is well reproduced by a relativistic Ferm i-gas calculation. The ability of the model to reproduce the Variation of the R-gamma data using the Goldberger-Treiman formula for g(P) sug gests there is no compelling reason to invoke a more exotic A-dependen t renormalization of g(P).