Etude de la multifragmentation dans les collisions centrales pour le systèmes $^(129)$Xe+$^(nat)$Sn entre 32 et 50 MeV/A : mesure de l'énergie collective d'expansion et du volume de freeze-out

Abstract : The multifragmentation of the nuclear system formed in the central collisions of the Xe+Sn reaction between 32 and 50 MeV/A has been studied with the INDRA detector. A tensorial analyse is used to select central collisions. An important part of the charge (about 85 %) is isotropically emitted. The charge partitions have the caracteristics of a simultaneous multiple fragment emission. The shape of the fragment kinetic energy distributions together with the reduced velocity correlation functions indicate that the fragmentation is a simultaneous process that occures at low density. A comparison between the experimental data and predictions of the statistical multifragmentation model of Copenhagen (SMM) shows that charge partitions agree with the hypothesis of a thermodynamical equilibrium, whereas, kinetic observables are more contraining to the model and difficult to reproduce. However, fragments correlation functions are used in order to extract the freeze-out volume and the collective radial energy. At 50 MeV/A, the freeze-out volume is estimated to be 2.7 times the normal volume. It decreases with incident energy evolves to be nearly twice the normal volume at 32 MeV/A. The collective energy evolves from 0 to 1.3 MeV/A with the bombarding energy. This expansion is not purely thermal and originates probably from a dynamical compression developpe in the early stage of the collision.
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Theses
Nuclear Theory [nucl-th]. Université de Caen, 1997. French


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Stéphanie Salou. Etude de la multifragmentation dans les collisions centrales pour le systèmes $^(129)$Xe+$^(nat)$Sn entre 32 et 50 MeV/A : mesure de l'énergie collective d'expansion et du volume de freeze-out. Nuclear Theory [nucl-th]. Université de Caen, 1997. French. <tel-00003688>

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