Experiment on doubly radiative thermal neutron capture in hydrogen

An upper limit of 1.5×10^?4 was measured for the branching ratio of the doublephoton to single-photon transition from the 2.2 MeV np capture state to the ground state of the deuteron. This result was obtained in a coincidence experiment with two Ge(Li) detectors. Based on the total cross section of 334.2 mb for the thermal neutron capture in hydrogen, the upper limit corresponds to a cross section of 49 μb for the two-photon emission in the energy region 46 keV<E _γ<2177 keV.