A Detector for Physics of Nuclear Reactions at Intermediate and Relativistic Energies
Central Collisions

Predicted many years ago, the collective expansion of hot and dense nuclear matter produced in heavy ion collisions was experimentaly evidenced only recently [1,2]. The measured mass dependence of the fragments' kinetic energy and their abundancy give strong support for the existence of an important collective expansion which cools down the dissasembling matter so that heavy clusters can exist.

Whenever there exists a local thermal distribution (i.e. vanishing total momentum in the local frame) superimposed on a collective velocity field, in the nonrelativistic approximation one obtains:


A model treatment of the dissasembling mechanism shows that v2flow+Coul has a complex dependence on the fragment mass. Nevertheless, deviations from a linear dependence of Ekin as a function of the fragment mass, as it was experimentaly confirmed, is not so large to make unrealistic a tentative to estimate the collective energy from the slope of the mean kinetic energy values as a function of the mass for the reaction products.
The model predictions-rfm (radial flow model) [pet] for the mean kinetic energy per nucleon compared with the experimental results for different azimuthal intervals for Au + Au central collisions at 250 A.MeV.