Fragmentation instabilities in nuclear systems

The fragmentation of nuclear systems, formed in proton- and heavy-ion-induced reactions in a wide energy range, is examined. The dependence of the fragment production cross section on the incident energy and on the temperature of the emitting source is compared to predictions of a theory of condensation. We find many instances where the fragmentation instability can be explained by and may be attributed to a liquid-gas phase transition. Our analysis suggests the occurrence of instabilities at a critical temperature of approximately 11 to 12 MeV, in accord with several theoretical predictions. Conventional nuclear effects, such as Coulomb barrier penetration, cannot fully describe the observed phenomena.