| Popis: |
The mechanism of the production of fast α-particles in 12 C induced reactions was studied over a wide range of bombarding energies (7.5–16.7 MeV/ A ) by measuring α-γ coincidences. Absolute cross sections for 160 Gd ( 12 C , αx n ) 168−x Er and 160 Gd ( 12 C , 2αx n ) 164−x Dy reactions, as well as inclusive α-particle production cross sections, have been determined. Depending on the bombarding energy, a fraction of 0.2–0.4 of the singles α-particles can be explained as resulting from incomplete fusion reactions ( 12 C, α) and ( 12 C, 2α) which correspond to a capture of “ 8 Be” and “ 4 He”, respectively. The remaining fragments of the projectile have, on the average, the beam-velocity energies and their angular distributions are forward peaked. Distributions of side-feeding to the yrast bands in the target-residue nuclei indicate that low partial waves are strongly hindered in the incomplete fusion reactions. The energy dependence of the cross sections for ( 12 C, α) and ( 12 C, 2α) incomplete fusion as well as for ( 12 C, 3α) projectile breakup is given. A generalized concept of critical angular momentum which explains a competition between complete fusion, incomplete fusion and breakup reactions is proposed. |
