Speaker
Description
Description of nuclear fission is still an important problem. This is proved by the existence of various models attempting to describe maximally possible characteristics of the investigated process.
Similar goal is also faced by the model developed [1, 2] in the present study, which describes the dynamics of fission of heavy nuclei in the low- and medium-energy range. It is based on the use of a multidimensional system of Langevin equations responsible for changing the deformation configuration of the fissile system, whose surface is given [3] by Fourier parametrization. The potential of the deformed compound nucleus is described within the macroscopic-mircroscopic approach [4].
In earlier works [1, 2], the model considered the dynamical change of only three parameters corresponding to the nucleus deformation. Their physical meaning corresponds to the elongation of the system, the asymmetry of the pre-fragments, and the thickness of the neck connecting them. This was sufficient to consider the fission process at the final stage - the descent from the last barrier, i.e., we used the pre-deterministic hypothesis of the unavoidable breakup of the system by splitting the nucleus into fragments. This assumption, together with certain initial conditions [2], made it possible to simplify the calculations of such fission characteristics as the mass and charge distributions of the fragments and the total kinetic energies, which were in good agreement with experiment.
In several papers [5 $-$ 8], where similar Langevin models are also used, the fission process was considered starting from the ground state of the system and, obviously, providing the system with sufficient excitation energy to overcome the fission barriers. Nevertheless, only few (e.g. [6, 8]) take into account the non-axiality of the nucleus shape, which has direct influence on fission barrier heights, which is crucial in low-energy fission. However, it is also important for understanding the influence of this parameter on the departure of pre-fission particles, e.g. neutrons.
Therefore, the aim of this work is to generalise the existing model to the four-dimensional case, introducing the nuclear surface non-axiality parameter. Together with taking into account temperature effects acting on the diffusion tensor and shells, the above-mentioned distributions of primary fragments of low-energy fission of actinide nuclei are obtained. The main focus of the work is the comparative analysis of the obtained results with previous ones, due to which the previously used hypotheses are evaluated. In addition new boundary conditions, artefacts and other difficulties encountered in the numerical solution of the four-dimensional system of stochastic Langevin equations are identified. The obtained conclusions allow us to improve the model and prepare it for new modifications.
References
[1] P. V. Kostryukov et al., Chin. Phys. C 45, 124108 (2021).
[2] P. V. Kostryukov and A. Dobrowolski, Phys. Rev. C 108, 024605 (2023).
[3] C. Schmitt et al., Phys. Rev. C 95, 034612 (2017).
[4] K. Pomorski et al., Chin. Phys. C 45, 054109 (2021).
[5] M. R. Pahlavani, and S. M. Mirfathi, Phys. Rev. C 93, 024622 (2016).
[6] A. J. Sierk, Phys. Rev. C 96, 034603 (2017).
[7] L.-L. Liu et al., Phys. Rev. C 103, 044601 (2021).
[8] F. A. Ivanyuk, C. Ishizuka, and S. Chiba, Phys. Rev. C 109, 034602 (2024).
| Section | Experimental and theoretical studies of nuclear reactions |
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