NEUTRON-PROTON BREMSSTRAHLUNG EXPERIMENTS

It is well known that charged particles emit bremsstrahlung radiation when they are accelerated. Classical electron bremsstrahlung occurs wh en a proton is emitted by an electron accelerated in the field of a nu cleus. The bremsstrahlung process also occurs in the scattering of nuc leons, for which it is the lowest energy inelastic process that can oc cur. Like electron bremsstrahlung, nucleon-nucleon bremsstrahlung also requires the exchange of a virtual particle to conserve energy and mo mentum. In electron bremsstrahlung a virtual photon is exchanged but w ith two nucleons a meson can be exchanged. Unlike electron bremsstrahl ung, in nucleon-nucleon bremsstrahlung the photon can originate from t he exchanged meson. This exchange contribution has been shown in calcu lations to be a significant fraction of bremsstrahlung events. Thus br emsstrahlung serves as a probe of exchange currents in the nucleon-nuc leon interaction. Because of a lack of a free neutron target or an int ense neutron beam, few measurements of neutron-proton bremsstrablung e xist, each having poor statistical accuracy and poor energy resolution . The white neutron source at the Weapons Neutron Research (WNR) targe t area at the Los Alamos Meson Physics Facility (LAMPF) produces neutr ons with energies from below 50 to above 400 MeV. Using time-of-flight techniques and a liquid hydrogen target, we are measuring the outgoin g photons of energies up to 250 MeV at gamma ray angles of around 90-d egrees relative to the incident beam. Protons scattered at very forwar d angles are also detected in coincidence with the gamma rays.