Contribution of several mechanisms to the alpha particle elastic scattering in the angle range near 180 deg

The contribution of exchange processes (heavy stripping and substitution) into the amplitude of the 25-30 MeV α-particle elastic scattering by 12C and 40Ca nuclei is examined taking into account the distortion of plane waves of initial and finite particles. The eikonal approximation is used for accounting for distortions. The matrix elements of exchange processes are calculated. The results of calculations show that the Wronskian cutoff radii are close to those which have been obtained for calculation of exchange processes in the plane-wave approximation. The moduli of the values defining the contribution of exchange processes to the total S matrix are plotted. Also presented are Argand diagrams and angular distributions for both reactions. It has been established that the account for exchange processes improves the agreement of theoretical curves with the experiment in the whole range of angles, as compared with the optical model