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 {sup 2}H and {sup 3}H particles. Small-angle correlations are reported in central collisions for 34{ital A} MeV {sup 40}Ar+{sup nat}Ag. High-velocity {sup 3}H and {sup 2}H particles follow a direct emission scenario with mean lifetime {tau}{similar_to}30{minus}60 fm/{ital c}. Fragmentation to Li is characterized by {tau}{similar_to}120 fm/{ital c}. Current model calculations suggest a delay time of {similar_to}100{minus}200 fm/{ital 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 {approx_lt}50 fm/{ital c} for expansion between direct emission and fragmentation. {copyright} {ital 1995} {ital The} {ital American} {ital Physical} {ital Society}.