Differential cross section for neutron-proton bremsstrahlung

The neutron-proton bremsstrahlung process $(np\to np\gamma )$ is known to be sensitive to meson exchange currents in the nucleon-nucleon interaction. The triply differential cross section for this reaction has been measured for the first time at the Los Alamos Neutron Science Center, using an intense, pulsed beam of up to 700 MeV neutrons to bombard a liquid hydrogen target. Scattered neutrons were observed at six angles between 12${}^{\circ }$ and 32${}^{\circ }$, and the recoil protons were observed in coincidence at 12${}^{\circ }$, 20${}^{\circ }$, and 28${}^{\circ }$ on the opposite side of the beam. Measurement of the neutron and proton energies at known angles allows full kinematic reconstruction of each event. The data are compared with predictions of two theoretical calculations, based on relativistic soft-photon and non-relativistic potential models.