The study of heavy and superheavy elements is important for understanding nuclear structure at the limit of stability where macroscopic and microscopic effects are delicately balanced. It is a benchmark domain for a rich variety of calculations including time-dependent Hartree-Fock (TDHF) and density functional theory (DFT). One difficulty in studying these nuclei is the low formation probability. There is limited reliability in models to predict the outcome of superheavy particle formation due to the significantly large number of degrees of freedom. The fusion-fission process is a key reaction to access heavy element formation. Experiments were performed at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University and at the Heavy Ion Accelerator Facility at Australian National University to measure fusion-fission excitation functions of two different combinations of Ca+Sm and K+Pb with varying neutron-richness. The excitation functions were measured at center-of-mass energies ranging from 1.1$\%$ to 0.9$\%$ above and below the predicted barrier heights. Measured cross sections were found to be comparable above the barrier regardless of neutron-richness. At and below the barrier, cross sections were enhanced for systems with positive Q-value neutron transfer channels. Furthermore the experiment performed at the NSCL was the first measurement of fusion-fission cross sections using the Active-Target Time Projection Chamber. This experiment demonstrated the successful reconstruction and identification of fission tracks and established the viability of performing similar experiments in the future.
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