Analysis of the sequential fission observed in collisions of¹⁰⁰Mo +¹⁰⁰Mo and¹²⁰Sn +¹²⁰Sn around 20 A·MeV

Events with 2, 3 and 4 heavy fragments (A≥20) detected in the reactions¹⁰⁰Mo +¹⁰⁰Mo at 18.7, 23.7 A·MeV and¹²⁰Sn +¹²⁰Sn at 18.4 A·MeV were analyzed by means of an improved version of the kinematic coincidence method. The phase-space distributions prove that 3- (and possibly 4-) body events predominantly originate from a two-step mechanism and are compatible with the hypothesis of a binary deep-inelastic interaction followed by the further fissionlike decay of one (or both) of the primary fragments. The characteristics of the fission step - mass asymmetry, relative velocity, in-plane and out-of-plane angles - have been reconstructed for the 3-body events and indications are found that nonequilibrium effects at the end of the deep-inelastic phase may influence the fissionlike decay.