Nonequilibrium effects in fragmentation

A. CHERNOMORETZ; M. J. ISON; S. ORTIZ; C.O. DORSO

Physical Review C

Año: 2001 vol. 64 p. 246061 - 246069

0556-2813

We study, using molecular dynamics techniques, how boundary conditions affect the process of fragmentationof finite, highly excited, Lennard-Jones systems. We analyze the behavior of the caloric curves ~CC!, theassociated thermal response functions ~TRF!, and cluster mass distributions for constrained and unconstrainedhot drops. It is shown that the resulting CC for the constrained case differ from the one in the unconstrainedcase, mainly in the presence of a ‘‘vapor branch.’’ This branch is absent in the free expanding case even at highenergies. This effect is traced to the role played by the collective expansion motion. On the other hand, wefound that the recently proposed characteristic features of a first order phase transition taking place in a finiteisolated system, i.e., abnormally large kinetic energy fluctuations and a negative branch in the TRF, are presentfor the constrained ~dilute! as well as the unconstrained case. The microscopic origin of this behavior is alsoanalyzed.