• New measurements of 100 exotic fissioning systems, 75 previously unmeasured, map the asymmetric fission island.
• The study establishes a connection between the neutron-deficient sub-lead region and the actinide region, clarifying the fission mechanisms.
• Data reveals the influence of the deformed Z = 36 proton shell in the light fragment during the fission of sub-lead nuclei, helping refine fission models.

Nuclear fission, the splitting of a nucleus into two fragments, is a critical process for understanding nuclear mechanisms and refining theoretical models. This study focuses on the distribution of fragment masses and charges, which is important for r-process nucleosynthesis, influencing astrophysical abundances and the origins of elements, as well as having energy applications. While asymmetric fragment distribution is known for actinides, symmetric fission typically dominates lighter elements. However, this research presents measurements from 100 exotic fissioning systems, connecting the sub-lead and actinide regions and highlighting the role of the Z = 36 proton shell in asymmetric fission.

• What: Measurements of charge distributions of fission fragments for 100 exotic fissioning systems, including 75 previously unmeasured systems, to map the asymmetric fission island.
• Who: Researchers from CEA, DAM, DIF, Université Paris-Saclay, CNRS, IJC Lab, IGFAE, University of Santiago de Compostela, GSI Helmholtzzentrum für Schwerionenforschung, and other international institutions.
• When: Experiment S455 was performed at GSI Helmholtzzentrum. Received: 04 October 2024, Accepted: 11 March 2025, Published: 30 April 2025.
• Where: GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany, and various collaborating institutions.

This study significantly advances our understanding of nuclear fission by providing a comprehensive map of the asymmetric fission island. The identification of the Z = 36 proton shell's role is a notable contribution. This research bridges the gap between the well-understood actinide region and the neutron-deficient sub-lead region, refining fission models, essential for predicting the behavior of nuclei with extreme neutron-to-proton ratios. This refinement has implications for understanding r-process nucleosynthesis and improving energy applications.

The measurements of charge distributions from 100 exotic fissioning systems provide valuable insights into nuclear fission mechanisms. The research highlights the role of the deformed Z = 36 proton shell in the fission of sub-lead nuclei, linking the sub-lead and actinide regions. The data obtained will help refine fission models, advancing our understanding of r-process nucleosynthesis and enhancing energy applications. Ongoing research may explore the broader implications of these findings on nuclear structure theory and nuclear astrophysics.