ar X iv : n uc l - th / 0 20 30 59 v 1 2 1 M ar 2 00 2 On pressure versus density dependence in statistical multifragmentation models 1

We show that the statistical multifragmentation model with the standard param-eterization of the free volume predicts a constant pressure as density approaches the normal nuclear density. This is contrary to the Raduta&Raduta result obtained by disregarding the center of mass constraint. It is demonstrated that in finite nuclear systems the partitions with small number of fragments play an important role. In recent years much efforts have been directed to investigating thermodynamical properties of finite nuclear systems (see e. g. refs. [1]). In the paper [2] the authors study the phase diagram of finite systems with a statistical model designed for describing nuclear multifragmentation. The authors' model follows the theoretical prescriptions developed earlier in refs. [3–5] and based on the assumption that fragments are formed at a low density freeze-out stage. Consequently, the thermodynamical characteristics calculated within such kind of models have adequate physical meaning at low densities only, e.g. ρ < ∼ (1 2 − 1 3)ρ 0 (ρ 0 ≈0.15f m −3 is the normal nuclear density), when individual fragments are singled out from the surrounding nuclear matter [3, 4]. However, the authors of ref. [2] have tried to apply their model for the higher densities ρ → ρ 0 by removing the physical assumption that fragments do not overlap. They have found that the model predicts a Van der Waals kind of phase diagram. In particular, the pressure P → ∞ at ρ → ρ 0 , as seen from Fig. 3 of ref. [2]. In this comment we want to demonstrate that this result can be misleading, even under assumption of overlapping fragments. Within the standard statistical treatment of finite systems, when the conservation laws are properly implemented, the pressure always remains finite, even in the limit ρ → ρ 0. In the statistical models [2–5] the volume (density) affects the partition probabilities via so called free volume V f determining the phase space available for the translational motion of fragments. It differs from the actual physical volume of the system V because of the finite size of the fragments and fragment-fragment interaction. In the standard canonical description 1 A comment on " Investigating the phase diagram of finite extensive and nonextensive systems " by Al.H.