โ Scribed by R. Ceuleneer
No coin nor oath required. For personal study only.
The formal expressions ofthe scattering amplitudes for 4He and SHe scattering are derived in the framework of the distorted wave Born approximation. The nuclear states are described by means of the quasi-boson model. The phase rules corresponding to the excitation of the one-boson states are obtained using the properties of the radial integrals and without an explicit evaluation of the distortion parameters of the incoming and the outgoing waves. The possibility of a significant calculation of the magnitude of the cross sections is discussed.
The diffraction model ~) is the model mostly used for the analysis of 0t-scattering. Its success lies in the prediction of a well-verified rule (the phase rule of Blair) between the parity of the one-phonon excited states and the phase of the corresponding angular distributions of the scattered ~-particles. This rule can also be obtained by means of a plane wave Born approximation 1) or by means of numerical calculations performed in the framework of a distorted wave Born approximation 2). In all these works the Bohr-Mottelson description of the target nucleus is adopted. This model, however, in which one postulates a priori the collective character of the states, does not reproduce very well the experimental nuclear spectra. Furthermore, the description of unnatural parity states (~s = (-)s+ 1) requires the use of two-phonon states for which no phase rule seems to exist 3, 4). For these reasons the use of a microscopic description for the target nucleus (the quasi-boson model s) for the single-closed shell nuclei and the particle-hole model 6, 7) for the double-closed shell nuclei) seems more promising. These models constitute, on one hand, an attempt to give a unified description of all nuclear levels, whether they are collective or not. On the other hand, they allow one to treat the states with unnatural parity as one-boson states in the same manner as the natural parity states. It must also be emphasized that the particlehole transformation is a special case of the general quasi-particle transformation; therefore no formal distinction needs to be made between the single-closed shell and the double-closed shell target nuclei. t R6p6titeur ~ l'l~cole Royale Militaire.
๐ SIMILAR VOLUMES
In an experimental study of 6He+p and 3H+p collisions at ~70 A MeV, the elastic scattering angular distributions were measured and the known excited state 6He~. 8 was observed. Comparative analysis of existing experimental data on proton elastic scattering by 4He, 6He, 6Li, 8He, 9Li, and ~ Li was pe