GSI Helmholtzzentrum für Schwerionenforschung Leads Global Ranking in Nuclear Isomer Discoveries

World record investigator and world record holder
Dr. Ivan Kojouharov (right) co-discovered 143 nuclear isomers, more than anybody else. The statistics were compiled by Professor Michael Thoennessen (left)

(IN BRIEF) GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt has achieved a world-leading position in the discovery of nuclear isomers, with 192 identified to date according to a new statistical analysis published in Atomic Data and Nuclear Data Tables. The ranking places GSI/FAIR ahead of all other research institutions, highlighting its significant role in nuclear physics research. Former researcher Ivan Kojouharov contributed to 143 isomer discoveries through his work on advanced detector technology. The achievements have been supported by GSI’s integrated accelerator infrastructure and specialized instruments such as the FRS fragment separator. Nuclear isomers play an important role in astrophysics and have potential technological applications, and further discoveries are expected with the future FAIR accelerator complex currently under construction in Darmstadt.

(PRESS RELEASE) DARMSTADT, 27-Feb-2026 — /EuropaWire/ — GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt has achieved a new scientific milestone, taking the leading position worldwide in the discovery of nuclear isomers, according to newly compiled statistics published in the journal Atomic Data and Nuclear Data Tables. The research center, where the international accelerator facility FAIR is currently under construction, has identified a total of 192 nuclear isomers, more than any other research institution globally.

GSI/FAIR has long been recognized for major contributions to nuclear physics, including the discovery of six superheavy chemical elements. The latest ranking highlights the facility’s prominent role in advancing knowledge about atomic nuclei and the structure of matter.

Discoverers of nuclear isomers
From left: Professor Zsolt Podolyak, University of Surrey (2nd place of the co-discoverers); Professor Christoph Scheidenberger, head of the GSI/FAIR research department “FRS/SFRS Experiments”; Professor Michael Thoennessen, Michigan State University, USA; Dr. Ivan Koujouharov, world record holder (retired, formerly GSI/FAIR research department “Nuclear Spectroscopy”)

Among the contributors, Dr. Ivan Kojouharov, a former member of the nuclear spectroscopy research department who retired last year, stands out for his role in the discovery of 143 nuclear isomers, placing him first worldwide among co-discoverers. Kojouharov’s work focused on the development of advanced germanium detector systems that were used extensively in experiments investigating nuclear isomers, leading to his involvement in a large number of scientific publications.

The success of GSI/FAIR in this field has been supported by its integrated accelerator infrastructure and advanced instrumentation. Researchers have access to a complete acceleration chain, including the UNILAC linear accelerator, the SIS18 synchrotron and the ESR experimental storage ring, allowing studies of nuclei across the entire periodic table. The FRS fragment separator has played a particularly important role by enabling scientists to isolate specific atomic nuclei from the products of nuclear collisions and analyze them for isomeric properties.

View inside the GSI Fragement Separator
The fragment separator FRS made a special contribution to the discoveries. This “sorting machine” can isolate specific nuclei from a multitude of fragments after a nuclear collision and examine them for isomerism.

Nuclear isomers are atomic nuclei that store unusually high amounts of energy and release it more slowly than typical nuclei. While most nuclei immediately emit excess energy, isomers can remain in excited states for measurable periods before returning to a more stable configuration, typically through gamma radiation emission. These nuclear states are relevant to astrophysical processes such as stellar nuclear reactions and the formation of heavy elements and also have potential applications in fields including medical imaging and the development of highly precise nuclear clocks.

The new statistical analysis was conducted by Professor Michael Thoennessen of Michigan State University, who evaluated all scientific publications reporting nuclear isomers with half-lives exceeding 100 nanoseconds. The study builds on earlier work tracking isotope discoveries, another area in which GSI/FAIR has played a leading role. In isotope discovery statistics, the late Professor Hans Geissel has held the individual record since 2013 with 279 discoveries, while GSI ranks among the top institutions worldwide.

Thoennessen visited GSI/FAIR during a meeting of the international NUSTAR research collaboration, which resumed regular scientific gatherings at the Darmstadt campus shortly after a fire incident in early February. The NUSTAR program focuses on studying nuclear reactions occurring in stars in order to better understand how chemical elements are formed throughout the universe.

The construction of the FAIR (Facility for Antiproton and Ion Research) accelerator complex in Darmstadt represents one of the largest scientific infrastructure projects in the world. FAIR will provide new opportunities to investigate the structure of matter and cosmic processes, including the discovery of additional isotopes and nuclear isomers. The facility will include the superconducting Super-FRS fragment separator, the successor to the existing FRS system.

Professor Thomas Nilsson, Scientific Managing Director of GSI and FAIR, noted that the new accelerator facility is expected to enable many further discoveries in nuclear physics and strengthen the research center’s position at the forefront of international science.

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SOURCE: GSI/FAIR