Origin of asymmetric fission in neutron-deficient mercury isotopes
In plain words
Mercury-180 was expected to split into two equal halves, zirconium-90 nuclei, but a 2010 experiment found it splits unevenly. Which nuclear structure makes the split uneven in this region, far from the uranium-like nuclei where uneven fission is common, is only partly understood.
Precise statement
Explain the asymmetric mass distribution observed in beta-delayed fission of $180\mathrm{Hg}$ (peaks near $A \sim 80$ and 100) and the evolution toward symmetric fission in heavier Hg and Pb isotopes. The answer is the shell structure of the pre-scission configuration or of the nascent fragments (for example octupole-deformed proton or neutron numbers) that controls the asymmetry, with quantitative yield predictions for neighbouring isotopes.
What would settle it
A microscopic calculation that reproduces the measured mass yields of 178,180,182Hg and correctly predicts the asymmetric-to-symmetric transition across the region before it is measured.
Status in the literature
Unverified note
Calculations attribute the asymmetry to deformed shell effects in the nascent fragments, and 2025 work studied how excitation energy and angular momentum move the transition in 180Hg.