At the heart of peripheral nuclear physics, the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany, has once again asserted its preeminence on the global research stage. Renowned for pioneering discoveries spanning chemical elements to exotic isotopes, this venerable institution now claims a remarkable new world record: the identification of an unprecedented number of nuclear isomers. This landmark achievement is captured in a recent comprehensive statistical analysis authored by Professor Michael Thoennessen of Michigan State University and published in the prestigious journal Atomic Data and Nuclear Data Tables.

Nuclear isomers—metastable states of atomic nuclei that conserve high excitation energy for unexpectedly prolonged periods—are essential to deepening our grasp of complex nuclear architectures and astrophysical nucleosynthesis processes. Over the course of many years of experimental investigation, the GSI/FAIR consortium has detected a cumulative total of 192 nuclear isomers, a feat unmatched by any other research facility worldwide. Propelled by an innovative integration of particle acceleration and advanced detection instrumentation, these findings testify not only to methodological ingenuity but also to the relentless curiosity driving experimental nuclear science.

Central to the success at GSI is the extraordinary contribution of Dr. Ivan Kojouharov, whose career dedicated to nuclear spectroscopy catalyzed the co-discovery of 143 individual nuclear isomers—more than any other researcher globally. His expertise in developing high-performance germanium detector arrays proved vital in numerous experiments, enabling exquisite resolution when measuring gamma radiation emitted by isomeric transitions. Dr. Kojouharov’s extensive publication record underscores his pivotal role in expanding the nuclear landscape through meticulous data acquisition and nuanced analysis techniques.

The sophisticated accelerator complex at GSI is a cornerstone of this achievement, comprising an elaborate chain of devices starting with the Universal Linear Accelerator (UNILAC), proceeding through the heavy-ion synchrotron SIS18, and culminating in the Experimental Storage Ring (ESR). This multi-tiered infrastructure uniquely facilitates experimental access to virtually all elements present in the periodic table, allowing researchers to induce nuclear reactions and isolate exotic isotopes under controlled conditions. Crucially, the Fragment Separator (FRS) functions as an ingenious “sorting machine,” spatially segregating newly formed nuclear fragments post-collision and enabling targeted scrutiny for isomeric states.

Nuclear isomers themselves exhibit a striking deviation from typical nuclear behavior. While most nuclei shed excess energy instantaneously upon excitation, isomers are hindered from rapid decay by internal quantum mechanical selection rules and nuclear structural idiosyncrasies. This results in metastable configurations capable of holding onto energy for durations ranging from microseconds to years before gamma emission restores the nucleus to its ground state. Studying these isomers unravels intricate nuclear potential landscapes and contributes vital insights into stellar processes such as rapid neutron capture (r-process) nucleosynthesis, which governs the cosmic production of heavy elements.

Beyond fundamental inquiry, nuclear isomers hold promise for innovative technological applications, including usage in medical diagnostic imaging techniques through their unique decay signatures. Moreover, some isomers have sparked interest as candidates for ultra-precise nuclear clocks, which could surpass the accuracy of contemporary atomic clocks by exploiting nuclear transition frequencies less susceptible to environmental perturbations. These applied research directions are intertwined with ongoing efforts to decipher the fine structure of nuclear energy levels and decay pathways.

Prof. Michael Thoennessen’s meticulous compilation consolidates all verified scientific publications on nuclear isomers with half-lives exceeding 100 nanoseconds, standardizing knowledge across a broad temporal scale. This database update complements his longstanding stewardship of isotope discovery statistics—another domain where GSI maintains a premier global standing. Notably, the late Professor Hans Geissel held the record for the discovery of 279 isotopes, a testament to the continuous lineage of excellence fostered at the center.

The international scientific collaboration NUSTAR, hosted for the first major meeting since the February fire at GSI, exemplifies the vibrant research community engaged with the FAIR (Facility for Antiproton and Ion Research) project. NUSTAR scientists delve deeply into nuclear reactions mimicking astrophysical environments, striving to elucidate element formation mechanisms active within stars and explosive cosmic events. The communal synergy at FAIR offers fertile ground for breakthroughs in both experimental nuclear physics and astrophysics.

Looking ahead, the construction of the FAIR international accelerator center presages even more profound discoveries. As one of the world’s largest and most ambitious research infrastructures, FAIR integrates next-generation superconducting fragment separators (Super-FRS) poised to enhance isotope separation capabilities beyond those of the conventional FRS. This technological leap is expected to accelerate the discovery rate of isotopes and nuclear isomers, extending the experimental reach into previously inaccessible regions of the nuclear chart.

Professor Thomas Nilsson, Scientific Managing Director of both GSI and FAIR, articulates the institution’s vision succinctly: to replicate cosmic phenomena within a state-of-the-art laboratory environment and secure a commanding position atop the leaderboards of nuclear discoveries. The convergence of scientific ambition, technical innovation, and interdisciplinary collaboration embodied in FAIR and GSI illuminates promising avenues for unraveling universal mysteries encoded in nuclear matter.

In summation, the record-setting discovery of nuclear isomers at GSI/FAIR underscores a significant chapter in the annals of nuclear physics research. It exemplifies how precision instrumentation, comprehensive accelerator suites, and dedicated scholarship synergistically advance our understanding of atomic nuclei and their astrophysical significance. As FAIR progresses, the anticipation of uncovering new exotic states fuels excitement within the scientific community, reaffirming GSI’s stature as a crucible for nuclear innovation and cosmic exploration.

Subject of Research: Discovery and characterization of nuclear isomers

Article Title: Discovery of nuclear isomers

Web References: DOI: 10.1016/j.adt.2025.101767

Image Credits: © L. Weitz, GSI/FAIR

Keywords

Physics, Nuclear physics, Nuclear reactions

Tags: astrophysical nucleosynthesis studiesatomic nuclei excitation energyexotic isotopes identificationexperimental nuclear physics techniquesFAIR accelerator facilityglobal nuclear research recordsGSI Helmholtzzentrum researchmetastable nuclear statesnuclear data statistical analysisnuclear isomers discoverynuclear spectroscopy advancementsparticle acceleration methods