Nuclear fission modes and fragment mass asymmetries in a five-dimensional deformation space

Abstract

Nuclei undergoing fission can be described by a multi-dimensional potential-energy surface that guides the nuclear shape evolution—from the ground state, through intermediate saddle points and finally to the configurations of separated fission fragments. Until now, calculations have lacked adequate exploration of the shape parameterization of sufficient dimensionality to yield features in the potential-energy surface (such as multiple minima, valleys, saddle points and ridges) that correspond to characteristic observables of the fission process. Here we calculate and analyse five-dimensional potential-energy landscapes based on a grid of 2,610,885 deformation points. We find that observed fission features—such as the distributions of fission fragment mass and kinetic energy, and the different energy thresholds for symmetric and asymmetric fission—are very closely related to topological features in the calculated five-dimensional energy landscapes.

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Figure 1: Asymmetric and symmetric fission probabilities for 227Ra as functions of the excitation energy in the fissioning nucleus.
Figure 2: Nuclear charge yield in electromagnetic-induced fission of 234U from ref.
Figure 3: Five-dimensional shape parameterization used in our potential-energy calculation.
Figure 4: Calculated potential-energy valleys and ridges and corresponding nuclear shapes for 228Ra.
Figure 5: Calculated potential-energy valleys and ridges and corresponding nuclear shapes for 234U.
Figure 6: Several saddle-point shapes for 256Fm and 258Fm calculated on the grid in ref. 22.
Figure 7: Calculated (white circles) and measured (black circles)26–28 average mass division in asymmetric fission for sequences of even isotopes of Th, U, Pu, Cm, Cf, and Fm.

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Acknowledgements

The calculations on which the results in this paper are based were carried out on the cluster of 4 Alpha processors at the TANDEM accelerator in JAERI in the winter of 1998–99 and subsequently on the AVALON cluster of 140 Alpha processors at Los Alamos. This research is supported by the US DOE.

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Correspondence to P. Möller.

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Möller, P., Madland, D., Sierk, A. et al. Nuclear fission modes and fragment mass asymmetries in a five-dimensional deformation space. Nature 409, 785–790 (2001). https://doi.org/10.1038/35057204

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