ADVANCED LANGEVIN DYNAMICS FOR PREDICTING SPIN DISTRIBUTIONS IN HEAVY-ION FUSION
DOI:
https://doi.org/10.53555/cdbes518Keywords:
Heavy-ion fusion, spin distribution, Langevin dynamics, nuclear dissipation, quasi-fission, compound nucleus, angular momentum, nuclear viscosityAbstract
The angular momentum (spin) distribution of compound nuclei formed in heavy-ion fusion reactions is a key quantity governing fission probability, gamma-ray multiplicity, and evaporation-residue survival. Traditional approaches based on sharp cutoff formulas, coupled-channel barrier penetration, or mean-field dynamics often fail to reproduce experimentally observed spin widths, especially near the Coulomb barrier and in reactions forming very heavy or superheavy systems. In this study, I developed and applied an advanced multi-dimensional Langevin framework to predict spin distributions in heavy-ion fusion, treating the reaction as a stochastic transport process in a collective coordinate space, including radial separation, deformation, mass asymmetry, orientation, and rotational degrees of freedom. Dissipation is modelled using one-body wall-and-window friction, whereas random forces obey the fluctuation-dissipation theorem. Deformation-dependent inertia and realistic nucleus-nucleus potentials were consistently incorporated. Simulations for representative reactions such as , , and reproduce the observed broadening of spin distributions with increasing beam energy, enhanced angular momentum damping in mass-asymmetric systems, and separation of fusion and quasi-fission events. The results demonstrate that advanced Langevin dynamics provides a robust and physically transparent tool for predicting spin distributions and for guiding the design of fusion reactions aimed at producing heavy and superheavy nuclei.
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