Timescale phenomena in multi — fragment processes

Abstract

Recent experimental results on the production of intermediate mass fragments (IMF) in reactions of 12C, 18O, 20 Ne, and 40 Ar on nat Ag and 197 Au at bombarding energies 30MeV ≤ E/A ≤ 84 MeV are reviewed. For all investigated reactions the average multiplicity of IMF's is ≤ 1.6, indicating that these reactions mark the threshold region for multi-fragment processes. Correlations between intermediate-mass fragments were measured for 18O induced reactions on natAg and 197Au at E/A = 84 MeV. An anticorrelation at low relative velocities is observed reflecting the proximity of the two IMF's at the point of creation. The timescales for IMF emission derived from these correlation functions are similar to those of binary decay modes which indicates a multi-sequential nature of multifragment emission. Furthermore, it is found that the excitation energy residing in the composite system before fragment emission is the key variable governing these processes.