Time scale for multifragmentation in intermediate energy heavy-ion reactions.

Abstract

Fragment-fragment correlations are used to probe the spatial-temporal extent of the emitting source in central $^{36}\mathrm{Ar}$${+}^{197}$Au reactions at E/A=35, 50, 80, and 110 MeV. The experimental two particle correlations are compared both with the Koonin-Pratt two-body formalism as well as a three-body Coulomb trajectory calculation. The spatial-temporal extent of the emitting system decreases with increasing incident energy. Within the context of a three-body Coulomb trajectory model the mean fragment emission time rises sharply as a function of the assumed density of the system until \ensuremath{\rho}/${\mathrm{\ensuremath{\rho}}}_{0}$\ensuremath{\approxeq}0.3. If one assumes a fixed density, the extracted mean emission time decreases with increasing assumed charge of the emitting system. Assuming \ensuremath{\rho}/${\mathrm{\ensuremath{\rho}}}_{0}$\ensuremath{\approxeq}0.3 the mean emission time \ensuremath{\tau} according to calculations using a three-body Coulomb trajectory model, is \ensuremath{\approxeq}115--135 fm/c at E/A=50 MeV and \ensuremath{\approxeq}75--100 fm/c at E/A=110 MeV. Comparisons with a generalized N-body Coulomb trajectory model demonstrate that the effect of interactions with other emitted particles is negligible. The prediction of a microcanonical model which includes pre-emission correlations between the fragments is compared to the measured correlation function at E/A=110 MeV.