Time-scale analysis of three-fragment emission in the 12.7 GeV 4He + 197Au reaction

The time-scale for emission of three fragments (Z ≥ 8) in the 12.7 GeV 4He + 197Au reaction has been studied using a sandwich configuration of the Makrofol polycarbonate track detector. In events with different multiplicity of heavy fragments (Z > 20), the differences of the correlation functions for relative angle and relative velocity between pairs of fragments have been studied in order to determine the fragment emission-time scale. A sequential decay mechanism for the excited residual nuclei was found to be consistent with experimental data. It was determined that the fragment emission-time decreased with decreasing multiplicity of heavy fragments: from 1000 fm/c for events with two heavy fragments, through 300 fm/c for events with one heavy fragment, to 40 fm/c for events with no emission of heavy fragments.