We present preliminary results from a systematic study of heavy-ion induced fission fragment mass-total kinetic energy distributions for compound nuclei ranging from 203Tl to 217Fr. The data indicate shell effects present in the actinide region persist for all measured nuclides and offers the first model-independent observation of fission modes Standard I and Standard II in 203Tl. Fission fragment mass and total kinetic energy distributions were analysed using a 2D fitting procedure. A systematic trend in the residuals between the data and the fitted model, which is comprised of the liquid drop mode with contributions from Standard I and Standard II, demonstrate the requirement of at least one more shell-driven fission mode closer to symmetry. This points towards at least one more deformed shell effect playing a substantial role in the fission of pre-actinide nuclei near stability.
Tran et al. (Wed,) studied this question.