Analysis of alpha inelastic scattering in the continuum

h~elastic scattering is generally studied with a direct interaction mechanism on low excited discrete levels. However the analysis of inelastic scattering in the cont inuum is able to include the very excited and statistical states and to give information concerning their distortion. (a, ~') angular distributions have been analysed by using a direct interact ion mechanism and the distorted-wave approximation with a collective-model form factor. The deformation parameter obtained from this analysis has been compared to those deduced for the f r s t excited states and also to a calculation of the strength of a collective excitation. Alpha spectra induced by 54.8 MeV incident alpha-particles are measured on several targets from ~IV to e~ mass range by using the I.P.N. Synchrocyclotron of Lyon. The overall resolution is mainly due to the 1.7 MeV incident-beam resolution. The identification of the scattered particles is made by a Goulding method. A three-detector telescope is used to ensure a good identification of the whole energy range (from 6 MeV up to 55 MeV). In order to avoid, for small angles, dead time and pile-up in the particle identifier, a single-channel analyser is interposed to strike out, before identification, most of the elastic scattered particles. The beam current is measured by a Faraday cup, the accuracy of this measurement being verified with two monitor counters. Rough data are then corrected for energy absorption in the target, normalized and expressed in the centre-of-mass system. Some energy spectra for 30 ~ 90 ~ 160 ~ are shown in Fig. 1. Calculations of the angular distributions are made by using the distorted-wave theory with a collective-model form factor. The interaction between the target and the projectile is represented with the help of a lmnsphericaI optical model. The spherical part, a Woods-Saxon potential, describes the scattering in the entrance and exit channels and the nonspherical part, parametrized by the deformation parameter fl, produces inelastic transitions. For an energy E and a transferred angular momentum L, the only adjustable factor is the deformation parameter