First applications of the HIPSE event generator

The predictions of an event generator, HIPSE (Heavy-Ion Phase-Space Exploration), dedi- cated to the description of nuclear collisions in the intermediate energy range, are compared with experimental data collected by the INDRA and INDRA-ALADIN collaborations. Spe- cial emphasis is put on the kinematical characteristics of fragments and light particles at all impact parameters for the system Xe+Sn between 25 and 80 MeV/u

New approach of fragment charge correlations in 129Xe+(nat)Sn central collisions

A previous analysis of the charge (Z) correlations in the $\Delta Z-$ plane for Xe+Sn central collisions at 32 MeV/u has shown an enhancement in the production of equally sized fragments (low $\Delta Z$) which was interpreted as an evidence for spinodal decomposition. However the signal is weak and rises the question of the estimation of the uncorrelated yield. After a critical analysis of its robustness, we propose in this paper a new technique to build the uncorrelated yield in the charge correlation function. The application of this method to Xe+Sn central collision data at 32, 39, 45 and 50 MeV/u does not show any particular enhancement of the correlation function in any $\Delta Z$ bin.Comment: 23 pages, 9 figures, revised version with an added figure and minor changes. To appear in Nuclear Physics

Dynamical effects in multifragmentation at intermediate energies

The fragmentation of the quasi-projectile is studied with the INDRA multidetector for different colliding systems and incident energies in the Fermi energy range. Different experimental observations show that a large part of the fragmentation is not compatible with the statistical fragmentation of a fully equilibrated nucleus. The study of internal correlations is a powerful tool, especially to evidence entrance channel effects. These effects have to be included in the theoretical descriptions of nuclear multifragmentation.Comment: 13 pages, 26 figures, submitted to Physical Review

Multifragmentation process for different mass asymmetry in the entrance channel around the Fermi energy

The influence of the entrance channel asymmetry upon the fragmentation process is addressed by studying heavy-ion induced reactions around the Fermi energy. The data have been recorded with the INDRA 4pi array. An event selection method called the Principal Component Analysis is presented and discussed. It is applied for the selection of central events and furthermore to multifragmentation of single source events. The selected subsets of data are compared to the Statistical Multifragmentation Model (SMM) to check the equilibrium hypothesis and get the source characteristics. Experimental comparisons show the evidence of a decoupling between thermal and compresional (radial flow) degrees of freedom in such nuclear systems.Comment: 28 pages, 15 figures, article sumitted to Nuclear Physics

Model-independent tracking of criticality signals in nuclear multifragmentation data

We look for signals of criticality in multifragment production in heavy-ion collisions using model-independent universal fluctuations theory. The phenomenon is studied as a function of system size, bombarding energy, and impact parameter in a wide range of INDRA data. For very central collisions (b/b_ma

Modélisation des collisions nucléaires aux énergies de Fermi : validation à l'aide des données INDRA

This thesis is about the study of nuclear reactions at intermediate energies. A dedicated phenomenological model has been developed and compared with experimental data collected within the INDRA collaboration. The model is detailed in the first part of the work. Largely based on experimental facts, it uses geometrical assumptions by considering both the degrees of freedom of the nucleons and of the nuclei. In a second part, the assumptions of the model are tested and validated. After a presentation of the phase space explored during the reaction, a global comparison between the model and the experiment is performed for the system Xe + Sn from 25 to 80 MeV/u bombarding energy. Before concluding, two specific studies, one dedicated to central collisions and the other to the decay modes of the quasi-projectile in peripheral reactions are presented.Ce mémoire concerne l'étude des réactions nucléaires aux énergies intermédiaires. Un modèle phénoménologique a été élaboré et validé à l'aide des données recueillies avec le multidétecteur INDRA. Le modèle est décrit dans la première partie de la thèse. Largement inspiré de l'observation expérimentale, il est basé sur des hypothèses géométriques en considérant conjointement les degrés de liberté des nucléons et des noyaux. La deuxième partie teste et valide ces hypothèses. Après une présentation de l'espace des phases exploré lors de la collision, une comparaison globale entre le modèle et l'expérience sur le système Xe + Sn de 25 à 80 MeV/u est présentée. Avant de conclure, deux études spécifiques, une dédiée aux collisions centrales et l'autre aux modes de décroissance du quasi-projectile dans les collisions périphériques sont détaillées

First applications of the HIPSE event generator

The predictions of an event generator, HIPSE (Heavy-Ion Phase-Space Exploration), dedi- cated to the description of nuclear collisions in the intermediate energy range, are compared with experimental data collected by the INDRA and INDRA-ALADIN collaborations. Spe- cial emphasis is put on the kinematical characteristics of fragments and light particles at all impact parameters for the system Xe+Sn between 25 and 80 MeV/u