TIME RELATIONSHIPS BETWEEN DIRECT PARTICLE-EMISSION AND FRAGMENTATION - A PROBE FOR NUCLEAR EXPANSION PRIOR TO FRAGMENT FREEZE-OUT

A previously unexploited experimental observable is used to explore emission times for intermediate mass fragments relative to directly emitted H-2 and H-3 particles. Small-angle correlations are reported in central collisions for 34A MeV Ar-40 + Ag-nat. High-velocity H-3 and H-2 particles follow a direct emission scenario with mean lifetime tau similar to 30-60 fm/c. Fragmentation to Li is characterized by tau similar to 120 fm/c. Current model calculations suggest a delay time of similar to 100-200 fm/c for expansion of the central collision zone prior to the onset of ''freeze-out'' into fragments. But the observed velocity difference spectra Limit the delay time to less than or similar to 50 fm/c for expansion between direct emission and fragmentation.