Investigation of inelastic alpha-particle scattering by O-16 nuclei with angular alpha gamma correlations

The double-differential cross sections for the reaction O-16(alpha, alpha gamma)O-16 at E(alpha) = 25.2 and 30.3 MeV are measured for scattering angles from 18 degrees to 162 degrees. All even spin-tenser components of the density matrix for the 3(-) (6.131 MeV) state and the majority of the components for the 2(+) (6.916 MeV) state of the residual nucleus are reconstructed in a model-independent way. The angular dependences of the differential cross section for this reaction with the excitation of low-lying states of the O-16 nucleus are measured, and the excitation functions for three scattering angles 38 degrees, 138 degrees, and 162 degrees are determined in the energy range 21-30 MeV. The angular dependence of the population of magnetic substates of the O-16 3(-) state at 6.131 MeV is presented. The experimental angular dependences are compared with the results of calculations performed for the collective-excitation mechanism taken into account by means of the coupled-channel method and for the mechanism involving the formation of a compound nucleus.