Enhanced Emission Of High-Energy Photons Perpendicular To The Reaction Plane In Alpha+Th Reactions

High-energy photon and neutron emission has been measured in coincidence with fission fragments in alpha + Th-232 reactions at 170 MeV. From measurements parallel and perpendicular to the fission plane, anisotropies relative to the reaction plane were determined. The in-plane/out-of-plane intensity ratio is 0.72(7) for photons with energies above 20 MeV and 11(3) for neutrons at 35 MeV. The result for high-energy photons can be explained by nucleon-nucleon bremsstrahlung if the initial flow of nucleons has a correlation to the reaction plane similar to the one observed for fast neutrons.