Intermediate mass fragment emission in heavy-ion collisions: Energy and system mass dependence

Nucleus-nucleus collisions can lead to highly excited systems that form hot compressed nuclear matter @1#. These systems expand due to thermal pressure @2#. The expansion can cause density fluctuations which recover to normal density @3# or expand indefinitely, leading to the onset of multifragmentation. This behavior is governed by the incompressibility of nuclear matter, which is determined by the lowdensity nuclear equation of state @4#. With increase in available energy, the system can develop from evaporation to multifragmentation to vaporization, signifying the liquid-gas phase transition of nuclear matter @5‐8#. Several experimental and theoretical investigations of the liquid-gas phase transition and critical phenomena of nuclear matter have been carried out @9‐15#. The process of multifragmentation has been successfully treated in terms of equilibration hypotheses and statistical approaches @14‐16#. To investigate the critical region of phase transition experimentally, one must study the decay from a single source over a wide range of beam energies. One way to achieve this goal is to study central collisions of symmetric systems. Emissions from such collisions are expected to be isotropic, supporting the idea that central collision events can be regarded as ‘‘singlesource’’ events. The formation of the various phases of nuclear matter in heavy-ion collisions has been investigated by measurements of nuclear species emitted from the excited systems. Theoretical studies indicate that it is most feasible to study the liquid-gas phase transition by observing multifragment emission from nucleus-nucleus collisions @17‐20#. Statistical nuclear multifragmentation is a signature of the transition of nuclear matter from a liquid phase into a phase of several nuclear fragments with a broad mass distribution. Numerous investigations of multifragment emission from excited nuclear systems have been carried out @21‐30#. The probability of multifragment emission is expected to increase as the excitation energy increases because of available phase