Isospin-dependent multifragmentation of relativistic projectiles

Abstract

International audienceThe N/Z dependence of projectile fragmentation at relativistic energies has been studied with the ALADIN forward spectrometer at the GSI Schwerionen Synchrotron (SIS). Stable and radioactive Sn and La beams with an incident energy of 600 MeV per nucleon have been used in order to explore a wide range of isotopic compositions. For the interpretation of the data, calculations with the statistical multifragmentation model for a properly chosen ensemble of excited sources were performed. The parameters of the ensemble, representing the variety of excited spectator nuclei expected in a participant-spectator scenario, are determined empirically by searching for an optimum reproduction of the measured fragment-charge distributions and correlations. An overall very good agreement is obtained. The possible modification of the liquid-drop parameters of the fragment description in the hot freeze-out environment is studied, and a significant reduction of the symmetry-term coefficient is found necessary to reproduce the mean neutron-to-proton ratios 〈N〉/Z and the isoscaling parameters of Z⩽10 fragments. The calculations are, furthermore, used to address open questions regarding the modification of the surface-term coefficient at freeze-out, the N/Z dependence of the nuclear caloric curve, and the isotopic evolution of the spectator system between its formation during the initial cascade stage of the reaction and its subsequent breakup

Theoretical study of projectile fragmentation in theSn112+Sn112and<

“…An ensemble of excited sources was assumed to represent the collision systems after the initial nonequilibrium part of the reaction and chosen as the starting configuration for the statistical description of the subsequent reaction stages. Its general form in the plane of source mass and excitation energy was adapted from previous studies [9][10][11] and the sensitivity of the experimental observables to the parameters required for the liquid-drop description of the primary excited fragments was evaluated [6]. With the present work, we demonstrate that the same approach can be used to describe the recent FRS data for similar projectiles and that comparable results concerning the required model parameters are obtained.…”

“…[8]] is a useful tool for describing the fragment production in peripheral heavy-ion collisions at high energy [6,10,11,18]. In the present work, we consider the ensemble approach with the same parameters that were used for the interpretation of the ALADIN data [6].…”

“…Information of this kind can be related to processes taking place during the collapse and explosion of massive stars and in the formation of neutron stars [1,2]. The isospin composition of the produced fragments was found to be especially important because it can be used for determining the strength of the symmetry energy during fragment formation in the hot and diluted environment [3][4][5][6], which is crucial for weak reaction rates in stellar matter [2].…”

“…In a previous study with the ALADIN forward spectrometer, the fragmentation of stable 124 Sn and radioactive 107 Sn and 124 La projectiles at 600 MeV/nucleon was measured and analyzed [6]. In particular, it was found that the charge and isotope yields, fragment multiplicities and temperatures, and correlations of various fragment properties can be well described within the statistical multifragmentation model [(SMM) Ref.…”

“…For more violent collisions associated with larger particle and fragment multiplicities, its strength needs to be reduced if an adequate description of the experimental data is to be achieved [5,6,12,13]. This observation was also made in the analysis of the experimental data of Liu et al [14] obtained at the MSU laboratory for the same projectiles and targets that were studied with the FRS, i.e., 124 Sn + 124 Sn and 112 Sn + 112 Sn, but at the lower energy of 50 MeV/nucleon [15][16][17].…”