Quasi-Free Scattering in the Reaction Be^9(p,pα)He^5 at 55 MeV

The reaction Be 9 ( p , p α)He 5 g'nd was studied by coincidence measurements of emitted protons and alpha-particles. The angular correlation distributions were obtained in three manners. All of the distributions have a maximum at a pair of angles which corresponds kinematically to the zero momentum of the recoil nucleus. The yields at the recoilless angles are almost proportional to the differential cross section of the free proton-helium elastic scattering at the corresponding angle. The absolute cross section and the width of the peak appeared in the angular correlation distribution are in fairly good agreement with the results given previously by the experiment on the reaction Be 9 (α, 2α)He 5 g'nd at 28 MeV.