Critical behavior in the coexistence region of finite systems

The liquid-gas phase transition in finite systems is studied within a lattice gas model in the canonical ensemble. Ln the coexistence region, the existence of conservation laws is shown to result in anomalies in the associated equation of state leading, for example, to negative compressibility clue to surface effects. The associated partitions exhibit scaling behavior inside the coexistence zone. When the thermodynamical limit is taken this scaling disappears while the anomaly of the equation of stale becomes the usual nonanalytical behavior. Therefore, in the fragmentation of small systems such as nuclei the experimentally observed critical behavior is demonstrated to be compatible with a first order phase transition because of finite size effects. [S0031-9007(99)08488-4].