Systematic Study of Quasifission in Ca-48-induced reactions

The production of superheavy elements through the fusion of two heavy nuclei is severely hindered by the quasifission process, which results in the fission of heavy systems before an equilibrated compound nucleus (CN) can be formed. The heaviest elements have been synthesised using Ca-48 as the projectile nucleus. However, the use of Ca-48 in the formation of new superheavy elements has been exhausted, thus a detailed understanding of the properties that made Ca-48 so successful is required. Measurements of mass-angle distributions allow fission fragment mass distribution widths to be determined. The effect of the orientation of prolate deformed target nuclei is presented. Closed shells in the entrance channel are also shown to be more important than the stability of the formed CN in reducing the quasifission component, with reduced mass widths for reactions with the closed shell target nuclei Sm-144 and Pb-208. Comparison to mass widths for Ti-48-induced reactions show a significant increase in the mass width compared to Ca-48-induced reactions, highlighting the difficulty faced in forming new superheavy elements using projectiles with higher atomic number than Ca-48.