Prospects for Production of New Superheavy Elements using Projectiles with Z \textgreater 20

Recent experiments have produced superheavy elements with atomic numbers up to Z $=$ 118 in complete-fusion evaporation reactions using projectiles of $^{48}$Ca, although projectiles with Z$_{\mathrm{p}}$ \textgreater 20 will be required for the discovery of heavier elements. A systematic study of the reactions of projectiles of $^{44,48}$Ca, $^{45}$Sc, $^{50}$Ti, and $^{54}$Cr with a variety of lanthanide targets has been conducted at Texas A{\&}M University. The products of these reactions are spherical, shell-stabilized nuclei near the N $=$ 126 shell. Excitation functions have been measured for numerous reaction combinations, and the data show a substantial reduction in cross section for reactions with Z$_{\mathrm{p}}$ \textgreater\ 20 compared to the reactions of $^{48}$Ca with the same targets. These data have been compared to a simple theoretical model which suggests that the probability of compound nucleus formation and the survival of compound nuclei are both negatively affected by the change from $^{48}$Ca. In these reactions, significant collective effects decrease the survival of the compound nuclei and defy the assumption that strong shell-stabilization will increase the cross section. These results suggest that the production of new spherical, shell-stabilized superheavy elements with Z \textgreater\ 118 could be very difficult. This talk will discuss the most recent results and their implications.