A new framework to investigate the systematics of fusion probabilities in heavy element formation: Application to Th isotopes

A new framework for comparing fusion probabilities in reactions forming heavy elements is presented, which eliminates both theoretical and experimental uncertainties, and gives new insights into systematic behavior. For the first time, it can be seen that in reactions forming neutron-deficient isotopes of Th, the probabilities of forming a compact compound nucleus after capture follow a simple universal trend at energies above the capture barriers, with the nuclear structure of the colliding nuclei having a smaller influence than the mass-asymmetry. Surprisingly, the yields of specific Th isotopes appear to have little dependence on the number of neutrons evaporated, contrary to general expectations from statistical decay.