8Dim calculations of the third barrier in $^{232}$Th and a conflict between theory and experiment on uranium nuclei

TL;DR

This study calculates the third fission barrier and minimum in $^{232}$Th using an advanced 8D model, revealing a shallow minimum consistent with experiments, but highlighting discrepancies with uranium nuclei data.

Contribution

First 8-dimensional deformation calculations of the third barrier in $^{232}$Th using the IWF method, including dipole distortion for comprehensive shape analysis.

Findings

Third minimum energy $E_{III}$ is shallow (~0.36 MeV), matching experimental data.

Contradicts the deep minima observed in uranium nuclei, indicating a need for further experiments.

The method achieves detailed saddle point mapping on a large deformation lattice.

Abstract

We find the height of the third fission barrier $B_{III}$ and energy of the third minimum $E_{III}$ in $^{232}$Th using the macroscopic - microscopic model, very well tested in this region of nuclei. For the first time it is done on an 8-dimensional deformation hypercube. The dipole distortion is included among the shape variables to assure that no important shapes are missed. The saddle point is found on a lattice containing more than 50 million points by the immersion water flow (IWF) method. The shallow third minimum, $B_{III}-E_{III}\approx 0.36$ MeV, agrees with experimetal data of Blons et al. This is in a sharp contrast with the status of the IIIrd minima in $^{232-236}$U: their experimental depth of $\geq3$ MeV contradicts all realistic theoretical predictions. We emphasize the importance of repeating the experiment on $^{232}$Th, by a technique similar to that used in the uranium nuclei, for settling the puzzle of the third minima in actinides.