Dissipative aspects in projectile fragmentation at 200 MeV/U

Peripheral collisions involving heavy ions at relativistic energies have been extensively studied for the last years. Such reactions lead to generally hot fragments [1,2], however the excitation energy is subject to large fluctuations and can reach low values [3]. The study of the energy dissipation, its coupling to other quantities such as the isospin and momentum of fragments are of interest because they carry information on the underlying mechanism, governing to a large extent production yields. Up to now this excitation energy has been essentially assessed from the effect of the evaporation stage on the {N}/{Z} ratio of fragments [1,2]. We report in this contribution on a direct measurement, in coincidence with heavy fragments, of particles which mainly come from the deexcitation stage of the quasi-projectile. This type of measurement provides information not only on the mean deposited energy, but also on the excitation spectrum. The experimental results will be discussed in view of two questions: are neutron-rich isotopes produced either by fluctuations in the energy deposition (low energy tail) or by fluctuations in the decay stage for hot primary fragments? Does a Glodhaber-type mechanism [4] (recoil effects) fully accounts for the width of the longitudinal momentum spectrum?