Results on two-, three-, and four-body events from the100Mo+100Mo and120Sn+120Sn collisions aroundE/A=20 MeV

Abstract

Events with 2, 3 and 4 heavy-fragments (A>20) have been detected in the reactions l~176 l~176 at E/A = 18.7, 23.7 MeV and 12~ t2~ at E/A= 18.4 MeV.The experiments were performed with an array of 12 detectors which together covered a large fraction of the forward hemisphere and allowed a high detection efficiency for these events. Masses and energies of all fragments have been reconstructed by means of an improved version of the kinematic coincidence method. The probabilities P~ and P4 of producing 3-and 4-body events were found to depend mainly on the dissipated energy rather than on the bombarding energy, thus indicating that their origin lies more in the decay properties of the excited fragments than in the dynamics of the interaction. Emission of light particles from the composite system is shown to become more relevant with increasing bombarding energy and may explain the drop of the P3 and P4 curves at high energy losses. Small deviations of the P3 and P4 curves at 23.7 A. MeV from those at lower bombarding energies were used to estimate the amount of a possible pre-equilibrium light particle emission as a function of impact parameter.

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

“…Our previous paper [3] showed that the 3-and 4-body events from the a~176 + l~176 and 12~ + ~2~ collisions at 18-24 A. MeV are compatible with a two-step mechanism consisting of an initial deep-inelastic collision followed by the sequential fission of one (or both) of its reaction fragments, although it was not possible to infer the real nature of the reaction mechanism just from kinematics on an event-by-event basis. The present paper proves the sequentiality of the mechanism and gives indications that the time scale of the fission step may be rather short.…”

Study of the fusion-fission process in the 35Cl +24Mg reaction

“…For heavier nuclear systems [19][20][21][22] ternary events arise when the reaction proceeds mostly via a sequential two-step mechanism :…”

“…The evidence of ternary breakup processes [19][20][21][22] has been primarily found at higher bombarding energies (E lab ≥ 10 MeV/nucleon) leading to their interpretation as an intermediate mechanism, sandwiched between the binary reactions that dominate at energies close to the interaction barrier and the fragmentation process that occurs when the energy brought into the compound system becomes comparable to the total nuclear binding energy.…”

“…The unambiguous observation of ternary breakup processes is restricted to certain heavier systems [19,22] where, following a first-step binary decay, one of the reaction products has a sufficiently low fission barrier to allow its subsequent breakup. At bombarding energies close to or above 20 MeV/nucleon this concept of sequential fission becomes inadequate as the time delay between successive breakup steps becomes indistinguishable from the prompt fragmentation.…”

Coulomb chronometry to probe the decay mechanism of hot nuclei

“…Only by detecting all reaction products in coincidence and achieving a full kinematical reconstruction event by event can we hope to better understand the underlying reaction and decay mechanisms. Such exclusive experimental data are relatively scarce for multibody exit channels in this energy range [4][5][6][7] leaving room for ambiguities in the interpretation of the reaction mechanism. New theoretical efforts are made to cover this energy range including time dependent microscopic approaches [8,9], transport models [10] and molecular dynamics calculations [11], which require comparison with new exclusive measurements in order to advance.…”