Fission mode properties from fragment mass distributions

¹ Department of Fundamental and Theoretical Physics, Research School of Physics, Australian National University, Canberra, ACT 2601, Australia
² Department of Nuclear Physics and Accelerator Applications, Research School of Physics, Australian National University, Canberra, ACT 2601, Australia
³ Facility for Rare Isotope Beams, Michigan State University, East Lansing 48824, USA

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Published online: 13 May 2026

Abstract

Fission fragment mass distributions often display multiple structures, commonly interpreted in terms of distinct "fission modes." These are usually obtained through multi-Gaussian fits of experimental yields, assuming each Gaussian corresponds to a separate fission channel. However, theoretical models define fission modes in terms of valleys in the potential energy surface (PES) near scission, raising questions about how these "Gaussian modes" relate to the underlying dynamics. We introduce a simple scission-point-inspired model to connect observed yield distributions with effective potentials, providing a means to identify "effective fission modes." Comparisons between Gaussian and effective modes reveal that multiple Gaussian components can correspond to a single underlying fission mode. Analyses of ¹⁸⁰Hg and actinide fission show that asymmetric and symmetric modes emerge naturally from the shape of the effective potential and its evolution with excitation energy.