Zeptosecond Dynamics of Superheavy Element Synthesis Reactions: The Role of Sequential Fission

Our understanding of quasifission and thus superheavy element formation may be hindered by sequential fission, a secondary process that results in three final quasifission fragments rather than the expected two. This net three-body process is typically rejected or not detected in typical binary measurements, potentially eliminating the fastest outcomes of superheavy element synthesis reactions and leading to an incomplete understanding of the true primary reaction dynamics. To overcome this, the CUBE detector array at ANU was used to measure two- and three-body outcomes of reactions of 28Si + 248Cm, allowing us to uncover the full mass split distribution in the primary binary decay. For fragments with a mass greater than 208Pb, we find that including three-body outcomes enhances the cross-section by up to two orders of magnitude over the two-body quasifission cross-sections alone. These results present clear evidence that sequential fission plays a significant role in superheavy element synthesis reactions and should be accounted for in future studies.