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The symmetry term in the nuclear equation of state and its density dependence are of highest interest in nuclear structure but also for astrophysical applications in which nuclear matter may appear with extreme values of density and neutron-proton asymmetry. Considerable efforts are therefore presently made in order to obtain experimental information on the symmetry term from studies of nuclear reactions in which compressed and expanded states of nuclear matter may be reached.The isoscaling phenomenon and its relation to the symmetry energy in the fragmentation of excited residues produced at relativistic energies were studied in two experiments conducted at the GSI laboratory. The INDRA multidetector has been used to detect and identify light particles and fragments with Z ≤ 5 in collisions of 12C on 112,124Sn at incident energies of 300 and 600 MeV per nucleon.In a very recent experiment with the ALADIN spectrometer, the possibility of using secondary beams for reaction studies at relativistic energies has been explored. Beams of 107Sn, 124Sn, 124La, and 197Au were used to investigate the mass and isospin dependence of projectile fragmentation at 600 MeV per nucleon.Isoscaling is observed in both experiments, and the deduced symmetry term coefficients decrease with increasing centrality to values below 15 MeV for low-density breakups in the more central collisions. Possibilities to extend this program to observables related to the high-density phase of the reaction will be discussed.
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