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Relaxation en forme et multifragmentation nucléaire

Abstract : This work concerns the characterisation of the multifragmentation reaction induced in central collisions Xe+Sn at 32 Mev/A measured with the INDRA detector. This characterisation informs on the degree of equilibration. A crucial aspect for those studies is the event selection. In this study two approaches have been used for the selection of the collisions of interest. The first approach lies on various centrality selectors (flow angle, emission angle of the biggest fragment, total multiplicity of charged particles). The second approach that constitutes an innovation in nuclear physics is the use of the self-organising maps of Kohonen. Such a method permits a sorting on topology of the events without using explicitly variables related to the shape. Both selection methods show the coexistence of at least two dissipation levels in the most central collisions. The self-organising map method permits to unfold those processes. The sample associated to the multifragmentation and to the highest conversion of the initial energy represents 5% of the total cross section. Whatever the selection method the mean shape of the source is elongated along the beam axis. This result shows an uncomplete relaxation of the shape degree of freedom. The experimental data are compared with a statistical multifragmentation model (SMM) including the deformation of the source and collective expansion energy. The characterisation of multifragmentation reaction in terms of size, excitation energy, collective expansion energy and deformation is independent of the selection method used. From this comparison we deduce that 70% of the available energy and 83% of the nucleons of the initial system have been equilibrated during the reaction.
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Submitted on : Friday, November 21, 2003 - 10:18:25 AM
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  • HAL Id : tel-00003803, version 1



Bertrand Bouriquet. Relaxation en forme et multifragmentation nucléaire. Physique Nucléaire Théorique [nucl-th]. Université de Caen, 2001. Français. ⟨tel-00003803⟩



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