Investigation of the N/Z of the heavy fragmentation residues: the isospin thermometer method

The mean N-over-Z (/Z) ratio of heavy fragmentation residues produced in relativistic heavy-ion collisions is investigated. The result gives indications for a break-up stage also in the reactions in which heavy fragments are formed. Data are analysed to extract the excitation energy at the beginning of the evaporation stage of the reaction and to deduce the freeze-out temperature of the break-up process. The temperature determined with this approach is consistent with the value found in the production of intermediate-mass fragments. (authors)