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

The A/Z dependence of projectile fragmentation at relativistic energies has been studied with the ALADIN forward spectrometer at SIS. A stable beam of (124)Sn and radioactive beams of (124)La and (107)Sn at 600 MeV per nucleon have been used in order to explore a wide range of isotopic compositions. Chemical freeze-out temperatures are found to be nearly invariant with respect to the A/Z of the produced spectator sources, consistent with predictions for expanded systems. Small Coulomb effects (DeltaT approximately 0.6 MeV) appear for residue production near the onset of multifragmentation.

The spallation of 56 Fe in collisions with hydrogen at 1 A GeV has been studied in inverse kinematics with the large-aperture setup SPALADIN at GSI. Coincidences of residues with low-center-ofmass kinetic energy light particles and fragments have been measured allowing the decomposition of the total reaction cross-section into the different possible de-excitation channels. Detailed information on the evolution of these de-excitation channels with excitation energy has also been obtained. The comparison of the data with predictions of several de-excitation models coupled to the INCL4 intra-nuclear cascade model shows that only GEMINI can reasonably account for the bulk of collected results, indicating that in a light system with no compression and little angular momentum, multifragmentation might not be necessary to explain the data. Spallation reactions play an important role in many domains ranging from astrophysics to intense neutron sources. Proton-induced reactions are also a way to study the de-excitation mechanism of a nucleus in a single hot source, and with less dynamical effects than in nucleusnucleus collisions. They are often described as a 2-step model, with an intra-nuclear cascade (INC) phase followed by a de-excitation phase. Inclusive data on light particles emitted in the spallation process and, more recently, data on spallation residues, helped considerably in improving the models [1]. However, these are not sufficient to provide a real insight into the reaction mechanism and the discrepancies observed between data and codes cannot be interpreted unambiguously with inclusive data. This is in particular due to the fact that the final observables are often both influenced by the cascade phase (especially by the remnant excitation energy) and by the de-excitation phase. A few more exclusive measurements exist but are generally limited to the study of the most violent collisions representing a small part of the total reaction cross-section (for a review see e.g. [2]).The need for a better understanding of spallation reactions motivated the design of the SPALADIN setup at GSI, which aims at measuring in inverse kinematics and in coincidence all the spallation products with a low center-of-mass (c.m.) kinetic energy, from neutrons to heavy residues. The restriction to low c.m. energies, in fact due to geometrical acceptance limitations, largely favors the detection of particles from the de-excitation rather than the cascade phase. This allows to use the particle multiplicities as an indication of the excitation energy (E ⋆ ) at the end of the cascade stage.The SPALADIN setup, partially described in [3], is based on the inverse kinematics technique where the ion beam is projected onto a liquid hydrogen target. The use of the large acceptance dipole magnet ALADIN permits to select the particles with a low c.m. kinetic energy. Among other detectors, the setup comprises the large area neutron detector LAND, which provides neutron multiplicities, a time-of-flight wall and the multitrack and multiple-sampl...

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A systematic study of isotopic effects in the break-up of projectile spectators at relativistic energies has been performed with the ALADiN spectrometer at the GSI laboratory. Searching for signals of criticality in the fragment production we have applied the model independent universal fluctuations theory already proposed to track criticality signals in multifragmentation to our data. The fluctuation of the largest fragment charge and of the asymmetry of the two and three largest fragments and their bimodal distribution have also been analysed.Comment: 6 pages, 4 figures, IX International Conference on Nucleus-Nucleus Collisions, Rio de Janeiro, Brazil, August 28 - September 1, 200