Inner Bremsstrahlung in Muon Decay

A measurement of inner bremsstrahlung in muon decay has been made using spark chambers, scintillators and fast oscilloscopes. The electron range distribution in graphite and the absolute rates were determined for electron-gamma-ray angles between 130 and 180 deg. For the electron and gamma-ray energies studied, the branching ratio of $\mu \to e+\gamma +\nu +\overline{\nu }$ to $\mu \to e+\nu +\overline{\nu }$ is predicted to be about ${10}^{-4\mathrm{}}$ over this angular range. The total number of inner bremsstrahlung events observed was 1805±43, which is in agreement with an expected number of 1889±283. The data were found to be in accord with the predictions given by electromagnetic corrections applied to the weak interaction.