Background: In earlier studies, spherical and quadrupole deformed nuclei with closed shells were found to be the most probable fission fragments in the decay of heavy-mass compound nuclei at low excitation energies. Recently, the disintegration of heavy-mass actinides gave evidence of pear-shaped fission fragments, in the mass-asymmetric region, due to extra stability provided by the shell-stabilized octupole deformed ${}^{144}\mathrm{Ba}$ $(Z=56)$ nucleus.

Purpose: In our theoretical work, we have done an exercise to analyze the possibility of octupole deformed fragments in the decay of light- and heavy-mass isotopes of thorium, i.e., ${}^{222,224,226,228,230}\mathrm{Th}^{*}$.

Method: To carry forward the above idea, the mass and charge dispersions of chosen Th isotopes have been analyzed by including deformations (up to ${\beta }_3$) and related cold optimum orientations within the dynamical cluster-decay model (DCM), which is based on the collective clusterization approach of quantum mechanical fragmentation theory. The above analysis is worked out at low excitation energy, which corresponds to the cold synthesis criteria.

Results: In the decay of considered Th isotopes, the minima of fragmentation potential and peaks of preformation probability appear in two regions, near symmetric and asymmetric, respectively due to the presence of quadrupole (${\beta }_2$) and octupole deformations (${\beta }_3$) of decay fragments. However, the emission of ${\beta }_3$-deformed fission fragments is prominent in the heavier isotopes of Th, i.e., ${}^{226,228,230}\mathrm{Th}^{*}$. The above result is in agreement with the experimentally obtained mass and charge distributions.

Conclusions: The disintegration of thorium isotopes into octupole deformed fragments in the asymmetric region signifies their relative stability, which is enhanced for ${}^{144}\mathrm{Ba}$ ($Z=56$) or in its vicinity.

• Received 7 November 2021
• Accepted 17 February 2022

DOI:https://doi.org/10.1103/PhysRevC.105.034605