Upper limit for the 1H(n, γγ)2H cross section

A value of (-0.8 +- 2.5) x 10-5 has been measured for the ratio of double-photon to single-photon emission following neutron capture in hydrogen for 600 keV < E/sub gamma/ < 1620 keV. The two Ge(Li) detectors used in the experiment subtended an angle of 850 at the H2O target and were shielded from each other to reduce the background from the cross registration of single γ rays. The upper limit of the measured two-photon cross section (-3 +- 8 b) is larger than conventional theoretical predictions (approx. 0.07 μb) for this energy range but smaller than the prediction (approx. 13 μb) obtained if one assumes a maximal nonorthogonality between the 3S np continuum state and the deuteron ground state