ABSTRACT
The study of reaction mechanisms aims mainly to classify collisions according to some global ‘topological’ features which, following the discussion in section 4.2.2, means the identification and the characterization of source(s). The topology of each collision is, to a large extent, related both to the impact parameter of the collision and to a partial or total transformation of the available centreof-mass kinetic energy of the relative motion between the two partners of the collisions into disordered motion (heat). This dissipation process is governed by several important ingredients. One of them is the relative velocity between the initial partners of the reaction v
. The corresponding reduced relative wavelength associated with a nucleon-nucleon collision then reads
(5.1)
where m is the nucleon mass. According to equation (5.1), the following values (in the case of symmetrical systems) of =2 = 6:5; 2:1; 0:67; 0:24 fm are obtained for 1, 10, 100 and 1000 MeV/u beam energies, respectively. These values have to be compared with the mean nucleon-nucleon distance in a nucleus (typically 2 fm). If =2 exceeds this distance, a collective behaviour of nucleons during the collision is expected. In other words, mean-field (one-body) effects overcome nucleon-nucleon collisions (two-body) effects. The situation will be reversed if =2 is smaller than the mean nucleon-nucleon distance. According to this criterion, it turns out that mean-field effects are expected to be dominant in the low-energy region (below 15 MeV/u).
