Two-body photodisintegration of 4He in the 100-360 MeV region.

Measurements of the differential cross sections for the He(y, n) He and He(y, p)3H reactions have been performed for photon energies in the 100 — 360 MeU region. Results were obtained for nucleon center-of-mass angles close to 60', 90', and 120' by detecting the recoiling nuclei with a magnetic spectrometer. Both (y,p) and (y,n) cross sections are forward peaked and fall rapidly as a function of photon energy. The (y,p) to (y,n) cross section ratio is in the range 0.7 — 1.3 at each angle and tends to increase with photon energy. The data are compared with a calculation by Gari and Hebach which includes meson exchange contributions. The magnitude and energy dependence of the cross sections are approximately reproduced, but the theory fails to describe the angular dependence and the cross section ratios.