Abstract
The pre- and post-scission neutron multiplicities are measured for the fission of 208Rn, populated with the reactions 30Si+178Hf and 48Ti+160Gd in the excitation energy range of 54.5 - 80.8 MeV. We found significant differences in the pre-scission neutron multiplicities of these two systems. Also, both the reactions exhibit an enhancement in the pre-scission multiplicity with respect to the existing data for the 16O+194Pt reaction populating 210Rn. The measured multiplicities are compared with the theoretical predictions obtained from the Langevin dynamical model for fission. Dynamical simulations are also performed to estimate the capture cross-sections. Contribution of the neutrons, emitted during the fusion process, is shown to be crucial in determining the neutron multiplicities for the present systems. Moreover, in case of the 48Ti+160Gd reaction, rapid quasi-fission dynamics prevents neutron emission from the thermalized target-projectile composite. The present measurement helps us to understand the relative importance of fusion and quasi-fission processes and their timescales depending on the entrance channel mass asymmetry.
Highlights
In heavy-ion induced reactions, the formation and decay of an equilibrated compound nucleus (CN) involve intricate manybody dynamics
The compound nuclear decay is studied with the Langevin dynamical model for fission, where the dissipation strength is adjusted to reproduce the experimental npre for our reference system of 16O+194Pt from which the neutron emission is neglected during fusion
To examine the role of entrance channel dynamics in heavyion induced reactions, we measured neutron multiplicities for the CN 208Rn populated via two reactions, 30Si + 178Hf and 48Ti + 160Gd, having different mass asymmetry
Summary
In heavy-ion induced reactions, the formation and decay of an equilibrated compound nucleus (CN) involve intricate manybody dynamics. Probes like multiplicities of neutrons [1,2,3], charged particles [4,5], and γ -ray [6,7,8] are widely used to understand the fusion-fission (FF) dynamics Among these observables, neutron emission is the dominant decay mode when the excitation energy of a compound system is sufficiently high. It is observed that QF, fast-fission [30] and per-equilibrium fission [31] events are negligible for this reaction, indicating the presence of only FF decay These experimental results suggest the absence of any considerable fusion delay and, the corresponding formation time for such an asymmetric entrance channel is assumed to be negligible in respect to any neutron evaporation. The compound nuclear decay is studied with the Langevin dynamical model for fission, where the dissipation strength is adjusted to reproduce the experimental npre for our reference system of 16O+194Pt from which the neutron emission is neglected during fusion
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