Microcanonical studies concerning the recent experimental evaluations of the nuclear caloric curve

Abstract

The microcanonical multifragmentation model from [Al. H. Raduta and Ad. )] is refined and improved by taking into account the experimental discrete levels for fragments with A ≤ 6 and by including the stage of sequential decay of the primary excited fragments. The caloric curve is reevaluated and the heat capacity at constant volume curve is represented as a function of excitation energy and temperature. The sequence of equilibrated sources formed in the reactions studied by the ALADIN group ( 197 Au+ 197 Au at 600, 800 and 1000 MeV/nucleon bombarding energy) is deduced by fitting simultaneously the model predicted mean multiplicity of intermediate mass fragments (M IM F ) and charge asymmetry of the two largest fragments (a 12 ) versus bound charge (Z bound ) on the corresponding experimental data. Calculated HeLi isotopic temperature curves as a function of the bound charge are compared with the experimentally deduced ones.

Modification of surface energy in nuclear multifragmentation

“…Here a 1 = 0.001 MeV −1 , and a 2 ≈ 0.009-0.015 MeV −2 slightly depends on the projectile energy. It should be noted that the adopted correlation of the mass number with the excitation energy is consistent with dynamical simulations [29,30], as well as with results of other statistical models [6,7,12]. Besides providing a very good description of fragment production at different Z bound , the calculations with this kind of ensemble also correctly reproduce the behavior of the caloric curve [18].…”

“…There are large fluctuations of the fragment multiplicity and of the size of the largest fragment in the transition region from a compound-like decay to full multifragmentation of spectators [3]. It was found that the statistical models, which assume a thermal equilibration among hot fragments in a freeze-out volume at subnuclear densities, are fully consistent with the data [4][5][6][7].…”

Hot fragmentation of nuclei

“…5 represent the results for 600 MeV per nucleon [51], with small modifications due to additional experimental information and corrections, and the results for 1000 MeV per nucleon obtained more recently [52]. The temperature of the transition region is close to that obtained with the dynamical [49] or statistical models [7,53,54] and does not change with the bombarding energy. In contrast to it, the energy associated with the spectator source increases by, on the average, 30% over the range 600 to 1000 MeV per nucleon, a behavior inconsistent with the universality of the spectator decay that so clearly appears in other variables [21].…”

“…It is motivated by the differences of the wave lengths and time scales governing the entrance and exit channels and justified by the remarkable success of statistical approaches for the second stage [5][6][7]. The intermediate states are not necessarily equivalent to hot nuclei but should be, more generally, viewed as systems of highly excited nuclear matter, populating a phase space characterized by global quantities like mass, charge, energy, density or temperature.…”

Nuclear multifragmentation and phase transition for hot nuclei

“…Finally generated events are filtered to account for the experimental device. Detailed presentations of models can be found in references [17,105,110,111,112]. Within such an approach the input parameters: mass and charge of the system at break-up density, its excitation energy, its volume at freeze-out and the eventual added radial expansion have to be backtraced to experimental data, estimated from dynamical simulations or derived from data related to properties of systems at break-up.…”