Isospin dependent thermodynamics of fragmentation

The thermal and phase properties of a multifragmentation model that uses clusters as degrees of freedom are explored as a function of isospin. Good qualitative agreement is found with the phase diagram of asymmetric nuclear matter as established by different mean-field models. In particular, from the convexity properties of the nuclear entropy, we show that uncharged finite nuclei display first- and second-order liquid-gas-like phase transitions. Different quantities are examined to connect the thermal properties of the system to cluster observables. In particular, we show that fractionation is only a loose indication of phase coexistence. A simple analytical formula is proposed and tested to evaluate the symmetry (free) energy from the widths of isotopic distributions. Assuming that one may restore the isotopic composition of breakup fragments, it is found that some selected isotopic observables can allow one to quantitatively access the freeze-out symmetry energy in multifragmentation experiments.