Speaker
Description
Nuclear fission is a complex quantum many-body process governed by the interplay between macroscopic liquid-drop properties and microscopic shell effects, which together determine the final fragment configuration. While early macroscopic approaches predicted predominantly symmetric mass splits for many systems, it is now well established that the quantum shell structure of the nascent fragments plays a decisive role in shaping the fission outcome. In particular, deformed shell gaps can favor asymmetric mass divisions, giving rise to the characteristic heavy-light fragment pattern observed across a broad range of fissioning nuclei. Recent high-precision measurements have identified a new region of asymmetric fission driven by shell effects in the light fragments, demonstrating that fragment-structure effects remain dominant even in previously unexplored areas of the nuclear chart.
To investigate this newly identified island of asymmetric fission, a dedicated experiment was performed at GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany, employing inverse kinematics at relativistic energies with the state-of-the-art R$^3$B/SOFIA setup. We report measurements of fission-fragment charge distributions for 100 exotic fissioning systems, establishing a direct link between the neutron-deficient sub-lead region and the well-known actinide region. These data provide a comprehensive mapping of the asymmetric-fission island and deliver clear experimental evidence for the decisive role of the deformed proton shell at $Z=36$ in sub-lead fission.
In addition, we systematically investigated global odd-even staggering in the fission-fragment charge distributions as a function of the fissioning system. Our analysis demonstrates that shell structure in the fissioning nucleus itself contributes significantly to the observed staggering.