An asymmetric fission island driven by shell effects in light fragments.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 40307545.
- Also identified by DOI 10.1038/s41586-025-08882-7 and PMC identifier 12646959.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Nuclear fission leads to the splitting of a nucleus into two fragments<sup>1,2</sup>. Studying the distribution of the masses and charges of the fragments is essential for establishing the fission mechanisms and refining the theoretical models<sup>3,4</sup>. It has value for our understanding of r-process nucleosynthesis<sup>5,6</sup>, in which the fission of nuclei with extreme neutron-to-proton ratios is pivotal for determining astrophysical abundances and understanding the origin of the elements<sup>7</sup> and for energy applications<sup>8,9</sup>. Although the asymmetric distribution of fragments is well understood for actinides (elements in the periodic table with atomic numbers from 89 to 103) based on shell effects<sup>10</sup>, symmetric fission governs the scission process for lighter elements. However, unexpected asymmetric splits have been observed in neutron-deficient exotic nuclei<sup>11</sup>, prompting extensive further investigations. Here we present measurements of the charge distributions of fission fragments for 100 exotic fissioning systems, 75 of which have never been measured, and establish a connection between the neutron-deficient sub-lead region and the well-understood actinide region. These new data comprehensively map the asymmetric fission island and provide clear evidence for the role played by the deformed Z = 36 proton shell of the light fragment in the fission of sub-lead nuclei. Our dataset will help constrain the fission models used to estimate the fission properties of nuclei with extreme neutron-to-proton ratios for which experimental data are unavailable.