12C(π+π+4He)8Be reaction at 60 Mev

The 12C(π+,π+4He)8Be reaction resulting in 8Be nuclei in ground and first excited states has been experimentally studied at the π+ energy of 60 MeV. The integral cross sections, momentum and angular distributions of 8Be nuclei, the energy spectra and angular distributions of α-particles, and the π+ scattering differential cross sections have been obtained. The data are analyzed in terms of the direct knock-out model accounting for the effect of nuclei. The contributions of the mechanisms of α-particle and 8Be direct knock-out and of the statistic decay of excited 12C nuclei into the reaction mechanism have been determined. The data for π+ obtained at 60 and 112 MeV are compared. It is shown that the difference in the production cross sections of 8Be(0) and 8Be(2.9) nuclei at the energies is brought about mainly by the mechanism of α-particle direct knock-out and by the two-stage process