Description of the asymmetric to symmetric fission transition in the neutron-deficient thorium isotopes: Role of the tensor force

In the present study, we have investigated the impact of the tensor force on fission paths, in particular the symmetric and asymmetric barriers in( 230)Th, Th-226 , Th-222, and Th-216 isotopes which display an asymmetric to symmetric fission transition. This analysis has been performed within the HFB approach with (Q(20), Q(30), Q(40)) as collective variable constraints, using the D1ST2a Gogny+tensor term interaction and comparing to the standard D1S Gogny interaction results. The effects from the tensor term on the potential energy surface landscape, and especially on barrier heights and its topology by opening a new valley in agreement with experimental data, are found to be crucial in the description of exotic actinide fission. We conclude that a tensor term should be integrated to the long range part of the effective interaction for a better description of the fission.