Two-photon decay in $n-p$ capture has been reported as having a branching ratio of ${10}^{-3\mathrm{}}$ relative to single 2.23-MeV $\gamma$-ray emission. It is suggested that this result can be explained by crosstalk effects between detectors due to single $\gamma$ rays, principally that associated with annihilation in flight following pair production. The shape of the observed $\gamma -\gamma$ coincidence spectrum is consistent with this type of crosstalk and the apparent two-photon branch is about what is expected from a rough calculation of the magnitude of the crosstalk effect.

• Received 2 June 1975

DOI:https://doi.org/10.1103/PhysRevLett.35.813