Speaker
Description
Nuclear fission is a nonequilibrium, large-amplitude collective process in which a nuclear many-body system evolves through a multidimensional collective space. The dynamics involve complex quantum fluctuations and correlation effects, while the underlying microscopic mechanism remains incompletely understood [2]. The time-dependent generator coordinate method (TDGCM) represents the nuclear wave function as a superposition of intrinsic states in collective deformation space. By solving time-dependent equations of motion in the collective-coordinate space, TDGCM can incorporate quantum fluctuations during fission. It is therefore one of the principal microscopic approaches to fission dynamics. Multiple collective degrees of freedom are excited cooperatively during fission. Accurately capturing their complex couplings in simulations within a finite-dimensional collective space remains a major theoretical challenge.
Existing microscopic studies generally parameterize nuclear shapes using spherical-harmonic expansions. Recent studies, however, have identified substantial limitations of this approach for highly deformed configurations at late stages of fission [3,4]. To address this issue, we implemented Fourier shape parameterization within point-coupling covariant density functional theory and derived the corresponding deformation operators. We then calculated the potential energy surface and collective mass tensor in a two-dimensional collective space and performed dynamical fission simulations [5]. For 226Th, the Fourier-parameterized collective space converges rapidly and describes highly elongated and scission configurations more effectively. TDGCM calculations in the Gaussian overlap approximation consequently provide an improved description of the fission-fragment distributions.
Recently, we extended the calculations to a three-dimensional deformation space by introducing the neck-size degree of freedom q4. We investigated its effects on the topology of the potential energy surface and on energy fluctuations. This extension provides a clear picture of the competition and evolution among multiple fission pathways. The smooth, gently varying three-dimensional potential energy surface and the rapid convergence of higher-order coordinates improve the treatment of quantum fluctuations and dynamical evolution. The calculations reproduce the measured peak positions and widths of the fission-fragment yield distributions. They also substantially improve predictions of the total kinetic-energy distribution.
References
[1] S. M. Seltzer and M. J. Berger, Nucl. Instrum. Methods B 12, 95 (1985).
[2] V. E. Lewis, Nucl. Phys. A 151, 120 (1970).
[3] N. Schunck and D. Regnier, Prog. Part. Nucl. Phys. 125, 103963 (2022).
[4] S. G. Rohozinski, Phys. Rev. C 56, 165 (1997).
[5] Z. Y. Li, Y. Su, L. L. Liu, Y. J. Chen, and Z. P. Li, Phys. Lett. B 866, 139509 (2025).