Single and mutual excitation of projectile and target in α-scattering

The projectile excitation of 4He exciting the Jsup(π) = 0+ state at Esub(x) = 20.1 MeV (α*) and the mutual excitation of projectile and target has been studied in α-scattering from 24Mg, 28Si, 40Ca, 58Ni and 90Zr at Esub(α) = 65 MeV. The monopole excitation of 4He has been detected by its breakup α* → p + t in a coincidence setup. The double folding approach for the description of the single and mutual excitation is discussed in which the rather large effect of recoil in the microscopic calculation of the inelastic form factor is taken into account. The microscopic DWBA calculation yields a good description of the structure of the angular distributions for the single excitation, but fails to reproduce the absolute cross sections. A possible explanation in terms of a drastically larger absorption for the final (α* + target) channel is discussed. As compared to the single excitation the mutual excitation is enhanced and in two cases even more strongly than the single excitation. For larger angles this effect is well reproduced by the calculations; however, at small angles an anomalous behaviour in the cross section for mutual excitation is observed. (Auth.)