In Xe+Sn central collisions from 12 to 20 MeV/A measured with the INDRA 4$pi$ multidetector, the three-fragment exit channel occurs with a significant cross section. In this contribution, we show that these fragments arise from two successive binary
splittings of a heavy composite system. Strong Coulomb proximity effects are observed in the three-fragment final state. By comparison with Coulomb trajectory calculations, we show that the time scale between the consecutive break-ups decreases with increasing bombarding energy, becoming compatible with quasi-simultaneous multifragmentation above 18 MeV/A.
FAZIA is designed for detailed studies of the isospin degree of freedom, extending to the limits the isotopic identification of charged products from nuclear collisions when using silicon detectors and CsI(Tl) scintillators. We show that the FAZIA te
lescopes give isotopic identification up to Z$sim$25 with a $Delta$E-E technique. Digital Pulse Shape Analysis makes possible elemental identification up to Z=55 and isotopic identification for Z=1-10 when using the response of a single silicon detector. The project is now in the phase of building a demonstrator comprising about 200 telescopes.
Recent advancement on the knowledge of multifragmentation and phase transition for hot nuclei is reported. It concerns i) the influence of radial collective energy on fragment partitions and the derivation of general properties of partitions in prese
nce of such a collective energy, ii) a better knowledge of freeze-out properties obtained by means of a simulation based on all the available experimental information and iii) the quantitative study of the bimodal behaviour of the heaviest fragment charge distribution for fragmenting hot heavy quasi-projectiles which allows, for the first time, to estimate the latent heat of the phase transition.
Recent important progress on the knowledge of multifragmentation and phase transition for hot nuclei, thanks to the high detection quality of the INDRA array, is reported. It concerns i) the radial collective energies involved in hot fragmenting nucl
ei/sources produced in central and semi- peripheral collisions and their influence on the observed fragment partitions, ii) a better knowledge of freeze-out properties obtained by means of a simulation based on all the available experimental information and iii) the quantitative study of the bimodal behaviour of the heaviest fragment distribution for fragmenting hot heavy quasi-projectiles which allows the extraction, for the first time, of an estimate of the latent heat of the phase transition.
The role played by the heaviest fragment in partitions of multifragmenting hot nuclei is emphasized. Its size/charge distribution (mean value, fluctuations and shape) gives information on properties of fragmenting nuclei and on the associated phase transition.
Fragment partitions of fragmenting hot nuclei produced in central and semiperipheral collisions have been compared in the excitation energy region 4-10 MeV per nucleon where radial collective expansion takes place. It is shown that, for a given total
excitation energy per nucleon, the amount of radial collective energy fixes the mean fragment multiplicity. It is also shown that, at a given total excitation energy per nucleon, the different properties of fragment partitions are completely determined by the reduced fragment multiplicity (fragment multiplicity normalized to the source size). Freeze-out volumes seem to play a role in the scalings observed.
Cross sections, kinetic energy and angular distributions of fragments with charge 6$le$Z$le$28 emitted in 78,82Kr+40C at 5.5 MeV/A reactions were measured at the GANIL facility using the INDRA apparatus. This experiment aims to investigate the influe
nce of the neutron enrichment on the decay mechanism of excited nuclei. Data are discussed in comparison with predictions of transition state and Hauser-Feshbach models.
Ensembles of single-source events, produced in peripheral and central collisions and correponding respectively to quasi-projectile and quasi-fusion sources, are analyzed. After selections on fragment kinematic properties, excitation energies of the s
ources are derived using the calorimetric method and the mean behaviour of fragments of the two ensembles are compared. Differences observed in their partitions, especially the charge asymmetry, can be related to collective energy deposited in the systems during the collisions.
Multifragmentation properties measured with INDRA are studied for single sources produced in Xe+Sn reactions in the incident energy range 32-50 A MeV and quasiprojectiles from Au+Au collisions at 80 A MeV. A comparison for both types of sources is pr
esented concerning Fisher scaling, Zipf law, fragment size and fluctuation observables. A Fisher scaling is observed for all the data. The pseudo-critical energies extracted from the Fisher scaling are consistent between Xe+Sn central collisions and Au quasi-projectiles. In the latter case it also corresponds to the energy region at which fluctuations are maximal. The critical energies deduced from the Zipf analysis are higher than those from the Fisher analysis.
