Four-fragment exit channel in the interaction of 1050 MeV 84Kr with U studied with mica detectors

The interaction of 1050 MeV, ⁸⁴Kr ions with natural uranium has been studied with the help of mica track detectors in the 2π configuration. Three ``direct'' and seven ``indirect'' events have been observed with four heavy fragments in the exit channel. These events represent a cross section of (16+/-6) mb for this channel. The correlated tracks of two of the direct events have been used for kinematical analysis. The results indicate a two-step reaction mechanism. In the first step a ``quasifission'' process takes place which is followed by the sequential fission of at least one of the first step masses.