Light particle emission in heavy-ion collisions

Some aspects of light particle emission in heavy-ion collisions are discussed over a broad energy region from about 10 MeV/nucleon up to relativistic energies of 1 GeV/nucleon. The appearance of high energy components above the equilibrium evaporation region of the spectra is shown to be a general feature. At all energies the contributions to this tail are likely to range from single nucleon-nucleon up to multiple nucleon collisions. Various theories have been developed to describe the processes, ranging from the microscopic models of DWBA, master equation, cascade and TDHF to the macroscopic hydrodynamic, participant-spectator and hot-spot reaction mechanisms. Various approaches to determining the size of the localised zones are presented, such as the geometry of the participant and hot-spot models, the formation of composite light particles by coalescence or by chemical equilibrium, and experiments on two particle intensity interferometry. Studies of the light particles, in particular the deuteron-proton ratio, to determine the entropy of the hot zone are also described. Although the observed excess at high energies is presently attributed to the influence of additional degrees of freedom, eg. from phase transitions, a note of caution is raised by similar studies at lower energies. It is possible that deuterons are also created by simpler mechanisms, eg. by the snowball and surface pick-up effects. Finally it is shown that the multiplicity of light particles, by probing the disintegration of the hot zone, can also give information on the equation of state of nuclear matter. (Auth.)