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

Abstract

Abstract. Events with 2, 3 and 4 heavy fragments (A > 20) detected in the reactions ~~176 + l~176 at 18.7, 23.7 A" MeV and ~2~ + ~Z~ 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.

Statistical reactions with memory and thermalized-nonequilibrated nuclear states

“…statistical reactions with memory. It was suggested [26] that the fission-like decay [25,26] is different from the mechanism of statistical fission observed after some deep-inelastic collisions with lower incident energy. This implies that with an increase in the energy and mass of the colliding ions (i.e.…”

“…time-delayed statistical (with fluctuating S-matrix) process [27][28][29]. The second step is the fission-like decay of the fragment of deep-inelastic reaction -also a statistical time-delayed process [25,26]. Indeed, the time duration of the strongly mass asymmetric fission-like process is estimated [25,26] to be about 10 −20 sec.…”

“…The second step is the fission-like decay of the fragment of deep-inelastic reaction -also a statistical time-delayed process [25,26]. Indeed, the time duration of the strongly mass asymmetric fission-like process is estimated [25,26] to be about 10 −20 sec. This means that the energy coherence length of the fluctuating reaction amplitudes is about 100 keV and therefore rules out the direct reaction mechanism of the fission-like decay in the second step.…”

“…This manifests itself in the survival of the spin and parity coherence along the two step chain of sequential statistical processes. It was assumed [25,26] that dynamical effects could be responsible for the in-plane angular asymmetry. However, one may ask what is the origin of these dynamical effects?…”

Coulomb chronometry to probe the decay mechanism of hot nuclei

“…This information is of great importance in view of constraining reaction models with predictive power in this energy regime. Several methods have been proposed for time-scale measurement in peripheral heavy-ion collisions, which are dominated by deep-inelastic reactions, neck formation and decay, and so-called dynamical fission of projectileor target-like nuclei [6,16,17]. Such methods were recently used to probe the isospin equilibration between projectile and target nuclei [18][19][20][21].…”