Generation, dynamics, and correlations of the fission fragments' angular momenta

Abstract

The generation of angular momentum in fissioning nuclei is not well understood. The predictions of different models disagree, particularly concerning the correlation between the fragments' angular momenta. In this article, a time-dependent collective Hamiltonian model is proposed to treat the generation of the angular momentum in the fission fragments due to the quantum uncertainty principle as well as the dynamics of the collective wave function during and after scission. The model is constructed in the framework of the frozen Hartree-Fock approximation using a Skyrme energy functional to extract deformations of the fission fragments as well as the interactions in a derived collective Hamiltonian. The fission reactions studied are ${}^{240}$Pu $\to$ ${}^{132}$Sn+${}^{108}$Ru and ${}^{240}$Pu $\to$ ${}^{144}$Ba+${}^{96}$Sr. The model can account for a large part of the angular momentum found in experimental data. The orientation of the angular momentum of each fragment is found to be mainly in the plane perpendicular to the fission axis, in agreement with the experiment. The magnitudes of the angular momenta in the two fragments are nearly uncorrelated, in agreement with the recent experimental data of Wilson et al., Nature (London) 590, 566 (2021). Some of the conclusions of the traditional collective vibration model are supported by the present model but some are not. Surprisingly, it is found that the angular momenta of the fragments are slightly correlated positively as in a wriggling mode. It is also found that the presence of an octupole deformation in a fragment can significantly increase the generated angular momentum.

14 pages, 15 figures

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Cited by in corpus (7)

• Spatial orientation of the fission fragment intrinsic spins and their correlations
• Microscopic Study of Spin Transfer in Near-Barrier Nuclear Reactions
• Disentangling the influence of excitation energy and compound nucleus angular momentum on fission fragment angular momentum
• Meaurement of spin vs. TKE of ${}^{144}$Ba produced in spontaneous fission of ${}^{252}$Cf
• Quantum-mechanical description of angular motion of fission fragments at scission
• Intrinsic spin distributions in multinucleon transfer reactions
• Microscopic theory of angular momentum distributions across the full range of fission fragments