Neutron-proton radiative capture cross section atTn=185MeV

The differential cross section for the reaction p(n,d)γ has been measured for center-of-mass angles between 0° and 65° at a neutron kinetic energy $T_{\mathrm{n}=185\mathrm{}}$ MeV. Assuming time-reversal invariance, our result is in essential agreement with the deuteron photodisintegration measurement at ${\theta }_{\mathrm{p}=0\mathrm{}}$° performed by Hughes et al. at Mainz. In addition to this confirmation of the absolute magnitude, our results, for the first time, provide information on the shape of the cross section distribution near 0°, i.e., the region where existing theories show the largest differences. This paper contains a detailed account of the experiment and a comparison with relevant experimental information. A discussion of some theoretical implications is also included. The best agreement with our data is obtained from these theories where relativistic corrections to the charge density are taken into account.