The character and prevalence of third minima in actinide fission barriers

TL;DR

This study systematically investigates actinide fission barriers to identify nuclei with third minima, revealing that only specific nuclei with certain proton and nucleon numbers exhibit shallow third minima, consistent with some experimental data.

Contribution

It provides the first large-scale systematic calculation identifying actinide nuclei with third minima in their fission barriers.

Findings

Third minima are found mainly in nuclei with 88 ≤ Z ≤ 94 and 230 ≤ A ≤ 236.

Third minima are less than 1 MeV deep in light Th and U isotopes.

Results align with some experimental data but differ from others.

Abstract

The double-humped structure of many actinide fission barriers is well established both experimentally and theoretically. There is also evidence, both experimental and theoretical, that some actinide nuclei have barriers with a third minimum, outside the second, fission-isomeric minimum. We perform a large-scale, systematic calculation of actinide fission barriers to identify which actinide nuclei exhibit third minima. We find that only a relatively few nuclei accessible to experiment exhibit third minima in their barriers, approximately nuclei with proton number $Z$ in the range $88 \leq Z \leq 94$ and nucleon number $A$ in the range $230 \leq A \leq 236 $. We find that the third minimum is less than 1 MeV deep for light Th and U isotopes. This is consistent with some previous experimental and theoretical results, but differs from some others. We discuss possible origins of these incompatible results and what are the most realistic predictions of where third minima are observable.