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Multifragmentation de systèmes lourds : partitions et signaux de transition de phases

Abstract : This work studies mononuclear systems produced in heavy ion collisions with large (peripheral : Au+Au) and small (central : Xe+Sn et Gd+U) impact parameters. These two classes of collisions need specific selections in order to isolate sources in thermal equilibrium (quasi-projectiles and quasi-fusion sources). We perform analyses on the statistical ensembles of events obtained after those selections to evidence phase transition signatures. First, a bimodal behaviour of the biggest fragment distribution, in peripheral
collisions, is related to an order parameter using a renormalisation with an equiprobable excitation energy
distribution constraint. A comparison with a canonical ensemble gives us information on the coexistence region
location. Then, we compare static and dynamical properties of fragments produced by these sources in peripheral and central collisions. Differences on fragment multiplicities and charge asymmetry of partitions are observed. They find their origins in the presence or not of a velocity field mostly related
to collective radial expansion during fragment formation. Analyses of the signal related to abnormal fluctuations of configurational energies and of the fossil signal related to spinodal decomposition for Au quasi-projectiles are performed to establish a link with the same signals already observed for central collisions. Finally, the location of events of the two types of sources in the E*- Z1 plane, are compared with a phase diagram, particulary the boundaries of the coexistence region deduced from the previous signals.
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Contributor : Eric Bonnet <>
Submitted on : Thursday, December 21, 2006 - 5:01:36 PM
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  • HAL Id : tel-00121736, version 1



Eric Bonnet. Multifragmentation de systèmes lourds : partitions et signaux de transition de phases. Physique Nucléaire Théorique [nucl-th]. Université Paris Sud - Paris XI, 2006. Français. ⟨tel-00121736⟩



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