New Insights into Element Synthesis from Heaviest Tin Isotopes

An international team of researchers, spearheaded by scientists from GSI/FAIR in Darmstadt, Germany, has made significant strides in understanding the r-process nucleosynthesis through groundbreaking measurements conducted at the Canadian research center TRIUMF in Vancouver. This collaborative study, published in the *Physical Review Letters* on July 4, 2025, centers on the first mass measurements of three extremely neutron-rich tin isotopes: tin-136, tin-137, and tin-138.

The high-precision measurements, combined with nucleosynthesis network calculations, provide new insights into the formation of heavy elements in the universe, particularly through the rapid neutron capture process, or r-process, which occurs in neutron star mergers. These isotopes reveal crucial data regarding neutron separation energy, which is vital in defining the r-process path on the nuclear chart.

Dr. Ali Mollaebrahimi, the first author of the study and a recently appointed FAIR Fellow at GSI/FAIR, emphasizes the implications of their findings: "These changes could affect the r-process path on the nuclear chart at large and even alter where the limit of stability in this region of the chart of nuclides lies."

The research identified unexpected changes in the behavior of tin nuclei, particularly beyond the magic neutron number N=82, noting a reduction in the pairing effect of the last two neutrons. This discovery is pivotal for physicists and astrophysicists alike, as it enhances understanding of nuclear forces and element formation in extreme astrophysical environments.

Dr. Timo Dickel, head of the GSI/FAIR research group on thermalized exotic nuclei, remarked on the significance of this achievement: “This marks a significant milestone made possible through long-term collaboration among scientists from several research groups in Germany and Canada.” He noted that the multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS), developed by the IONAS group, played a critical role in the successful measurements.

The MR-TOF-MS was installed and commissioned at TRIUMF for initial experiments in 2017, and this year alone, the collaboration has resulted in two additional high-level publications related to element synthesis and nuclear structure. Notably, the mass spectrometer has previously enabled the discovery of the isotope ytterbium-150, marking a historic achievement in the realm of isotopic research.

The results from this study not only contribute to the understanding of nucleosynthesis but also play a key role in the FAIR Phase 0 activities, where young researchers are trained with cutting-edge tools for future experiments related to the MATS and Super-FRS Experiment collaborations at the FAIR facility.

In summary, the research conducted by GSI/FAIR and TRIUMF sheds light on the intricate processes behind element synthesis in the cosmos, paving the way for further exploration in nuclear physics and astrophysics. The implications of these findings extend beyond the realm of theoretical inquiry, potentially influencing future experimental designs and our understanding of the universe's elemental composition.