Investigation of processes competing with fusion in heavy ion reactions using ⁴⁰Ca and ⁵⁴Cr projectiles

Full text: The formation of new superheavy elements (SHEs) through heavy ion fusion reactions is a topic of great interest in nuclear physics. As the charge product of two colliding nuclei increases, fusion is dramatically hindered by competing processes such as deep inelastic collisions (DICs), transfer-fission and quasi-fission. To maximize the probability of forming a compound nucleus in experiments aimed at forming new SHEs, the choice of projectile and target must be made carefully. Currently, Calcium-48 beams are being used for SHE formation, but to form significantly heavier elements, beams of chromium have been proposed as good candidates. Therefore, the exploration of chromium reactions not only give an insight into the formation of the next heavy element and but also informs the development of reaction dynamics in heavy ion collisions through the study of the processes that compete with fusion. The work being presented here is aimed to investigate factors leading to fusion suppression in heavy ion reactions. We conducted a series of experiments with heavy projectiles ⁴⁰Ca and ⁵⁴Cr at beam energies ranging from well below to above fusion barrier, using the Australian National University 14UD tandem accelerator, superconducting linear post-accelerator and CUBE binary fission spectrometer. Using kinematic characteristics of two-body and three-body reactions outcomes, we identified quasi-fission and transfer-fission, which occur following energy dissipation. In this work, we will present a study of quasi-fission and energy dissipative processes in the collisions ⁴⁰Ca, ⁵⁴Cr + ²³²Th and ⁴⁰Ca, ⁵⁴Cr + ²³⁸U, investigated through measuring mass-angle distributions (MADs). We found strong mass-angle correlations in MADs for all reactions studied, clear evidence of fast quasi-fission. We also observed a high yield of three body events, indicating a high probability for other energy dissipative processes. (author)