Sensitivities of the relative velocity between fragments on the decay mechanism

Relative velocity spectra of two intermediate mass fragments (IMF) emitted in 18O induced reactions on 197Au at E/A=84 MeV were investigated. The average relative velocity measured at small and also large relative angles is satisfactorily reproduced by calculations that model the sequential emission of IMF's and light particles on the basis of statistical model calculations. A similar agreement is found for the average relative velocity measured in α+197Au reactions at E/A=800 MeV. Thus, no conclusive evidence for a transition from a conventional multi-sequential decay to a true multifragmentation process can be found at an excitation energy between 3 and 4 MeV per nucleon. (orig.)