Exchange effect in the scattering of an α-particle by light nuclei

Abstract

Exchange effects are discussed in the elastic and inelastic scattering of an α-particle by light nuclei. It is pointed out that, in addition to the well-known exchange scattering, there is another sort of exchange effect which corresponds to the heavy-particle-stripping in a nuclear rearrangement collision. This process is shown to play an important role in the angular distribution in the backward direction when the structures of both the target and residual nuclei are amenable to the α-cluster model. In the cut-off Born approximation the cross section for the process is presented in such a form as to contain no energy-dependent adjustable parameters, by making use of the technique developed in our previous papers.The elastic scattering of α-particles by C12 is analysed in the energy region between Eα = 15 MeV and 42 MeV; it is found that the very sharp backward peaking observed by Wong and Bleuler and by Corelli, Bleuler and Tendam in the angular distribution at about Eα = 18 MeV can be satisfactorily reproduced by the calculation. The reduced width of the α-particle is determined for the ground state of C12.The cluster structure of C12 is discussed. It is suggested that the ground state of C12 should be a mixture of the fourth order oscillation 3s, 2d and 1g states in the Be8-α-cluster representation, the mixing ratio of the 3s state being at most 12. Several experiments are discussed which could confirm the reaction mechanism leading to backward peaking.