Radiativeμ−Capture in Copper

The radiative capture of negative muons in copper (${\mu }^{-}+\mathrm{Cu}\to \mathrm{Ni}+\nu +\gamma$) has been measured. The muons were captured in the copper plates of one spark chamber and the gamma rays converted in the lead plates of a second spark chamber. A large (8-in.×8-in.) NaI crystal was used to measure the gamma-ray energy. The apparatus was sensitive to gamma rays of energy larger than 50 MeV. The observed gamma-ray spectrum is compared to a theoretical spectrum based on a Fermi-gas model of the nucleus. This results in values for the branching ratio for radiative muon capture relative to ordinary muon capture of $R=(4.6\mathrm{}\pm 0.7)\times {10}^{-4\mathrm{}}$ for $M^{*}=M_p$ and $R=(5.2\mathrm{}\pm 0.8)\times {10}^{-4\mathrm{}}$ for $M^{*}=\frac{M_p}{2}$; where $M^{*}$ is the effective nucleon mass used in the model, and $M_p$ is the mass of the proton. An attempt is made to extrapolate the observations in copper to what might be expected for the case of a free proton.