Observation of Two-Photon Decay inn−pCapture

Abstract

Coincident $\ensuremath{\gamma}$ rays of total energy 2.22 MeV, the deuteron binding energy, were observed following the capture of subthermal neutrons by an ${\mathrm{H}}_{2}$O target. The differential cross section, assuming a $\frac{1}{v}$ neutron energy dependence, increases from about 0.2 \ensuremath{\mu}b/keV at equal $\ensuremath{\gamma}$ energies to about 1.0\ensuremath{\mu}b/keV for a $\ensuremath{\gamma}$ energy of 1600 keV. The branching ratio for emission of two $\ensuremath{\gamma}$ rays, both in the $\ensuremath{\gamma}$-ray energy range from 600 to 1620 keV, to single 2.22-MeV $\ensuremath{\gamma}$ rays was found to be (1.05\ifmmode\pm\else\textpm\fi{}0.16)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$.