ON THE FORMATION OF HOLLOW CONFIGURATIONS IN HEAVY-ION COLLISIONS

The formation of the so-called hollow configurations, ie. regions of l ow density, during the expansion of an excited nucleus is investigated . It is argued that these subnormal density regions are a direct conse quence of the liquidlike behavior of compressed nuclear matter. To stu dy this, the free isotropic expansion of an initially hot and dense sp here of nuclear matter is investigated using the hydrodynamic equation s coupled to a simple, but realistic, equation of state. An approximat e solution of these equations is obtained using a novel similarity met hod. The observed behavior of the radial nuclear density shows the app earance of subnormal density regions and matter shells early in the ex pansion. This result occurs for all values of interest of the nuclear compressibility but only for certain initial conditions of the velocit y, thus confirming the possibility of creating hollow configurations d uring the break-up of nuclei as predicted by other numerical calculati ons.