MULTIFRAGMENTATION IN INTERMEDIATE ENERGY NUCLEUS-NUCLEUS COLLISIONS

Multi-fragment disintegrations have been investigated for Xe-129+ Au-197 collisions at E/A = 50 MeV and Ar-36+ Au-197 reactions at E/A = 35, 50, 80 and 1 10 MeV with a low threshold 4-pi multi-fragment detection array. For the Xe-129+ Au-197 system, the average number of intermediate mass fragments (Z = 3-20) increases strongly as a function of charged particle multiplicity and reaches values slightly larger than six for the most violent collisions. This is the largest mean fragment multiplicity yet observed. Molecular dynamics, bond percolation models, and conventional compound nuclear statistical decay calculations all predict far too few fragments for these systems. Reasonable agreement with the experimental data is obtained for statistical model calculations which assume the system breaks up at densities significantly less than normal nuclear density. The intrinsic excitations of emitted fragments are more consistent with thermal models for central collisions with large charged particle multiplicities than for less gentle peripheral collisions.