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 2H and 3H particles. Small-angle correlations are reported in central collisions for 34AMeV 40Ar+natAg. High-velocity 3H and 2H particles follow a direct emission scenario with mean lifetime τ∼30-60fm/c. Fragmentation to Li is characterized by τ∼120 fm/c. Current model calculations suggest a delay time of ∼100-200fm/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 50 fm/c for expansion between direct emission and fragmentation.