Fragment emission time from well defined sources in58Ni+197Auat 34.5 MeV/nucleon

Abstract

We have measured two-fragment correlation functions of the intermediate mass fragments emitted from quasiprojectile sources and midrapidity component formed in ${}^{58}\mathrm{Ni}{+}^{197}\mathrm{Au}$ at 34.5 MeV/nucleon. The two-fragment correlation functions of midrapidity component show a stronger Coulomb suppression than the quasiprojectile source. This Coulomb suppression for midrapidity component changes very little with the excitation energy of the quasiprojectile source deduced event by event by calorimetry method. By comparing the experimental correlation functions with an N-body Coulomb trajectory code calculation, the emission time of quasiprojectile sources has been extracted as a function of the excitation energy. The emission time decreases monotonically with the excitation energy in the range of 2--6 A MeV from 550 $\mathrm{fm}/c$ to about 150 $\mathrm{fm}/c.$ Above excitation energy of $6A$ MeV, the emission time becomes shorter and constant, suggesting that prompt multifragmentation occurs in these quasiprojectile sources.