In a groundbreaking advance in nuclear physics, researchers have performed the first ever ab initio calculation of the rarest and most complex electromagnetic transition observed in atomic nuclei: the hexacontatetrapole E6 transition in the isotope iron-53 (^53Fe). This achievement marks a significant milestone in the understanding of nuclear structure under extreme conditions and demonstrates the power of modern computational techniques to describe intricate nuclear phenomena without resorting to empirical adjustments. The research offers fresh insights into the nature of high-multipole electromagnetic decays within nuclei, with important implications for both theoretical frameworks and future experimental analyses.
The transition in question involves an isomeric state in ^53Fe characterized by an exceptionally high angular momentum of 19/2^− and a half-life of 2.54 minutes, residing at an excitation energy around 3.0 MeV above the ground state. What sets this nuclear isomer apart is the uniquely allowed electromagnetic decay pathway: a single-photon emission carrying a massive angular momentum quantum number of six (6ħ). This kind of hexacontatetrapole transition, identified by the multipolarity E6, is extraordinarily rare—so rare, in fact, that while analogous high-multipole emissions exist in other quantum systems, such as solid hydrogen matrices or atomic rubidium, ^53mFe remains the only known nuclear system to exhibit this phenomenon spontaneously and without external excitation.
Crucial to the success of this study is the application of the valence-space in-medium similarity renormalization group (VS-IMSRG) method. This advanced computational approach allows the nuclear many-body problem to be tackled starting from realistic nuclear forces derived from chiral effective field theory. Unlike traditional models of nuclear electromagnetic transitions, which often rely on effective charges tuned to match experimental data, the VS-IMSRG framework employs bare nucleon charges for all multipolarities, offering a truly predictive and parameter-free description of complex nuclear processes. This lends considerable credibility and robustness to the findings, setting a new standard for theoretical nuclear physics.
The researchers employed two distinct sets of chiral nucleon-nucleon plus three-nucleon interactions to interrogate the structure of ^53Fe and its isomeric states within extensive model spaces reaching up to e_max = 14 and E_3max = 24, enabling the precise calculation of excitation energies and transition probabilities. Such large-scale computational resources provide the convergence necessary to accurately predict the extremely delicate observables linked to high-multipole transitions, which have hitherto been a formidable challenge for nuclear theorists. The convergence of results across different interaction models further underscores the reliability of the ab initio approach.
One of the striking conclusions from the calculations is the confirmation that the 19/2^− isomer in ^53Fe gains its stability and unique decay characteristics primarily from a pure orbital configuration dominated by the 0f_7/2 shell occupancy. This simplification of the nuclear wavefunction contrasts with more complicated configurations found in other nuclei, suggesting a relatively clean testbed for studying extreme electromagnetic processes in nuclear matter. The ability to describe the isomer’s life and decay properties accurately using this orbital framework bolsters confidence in both the computational model and the nuclear shell model foundations.
Beyond merely reproducing known experimental data, the study pioneers the ab initio calculation of transition probabilities for the E6, M5, and E4 multipolarities within the nuclear electromagnetic decay spectrum of ^53Fe. This comprehensive treatment is unprecedented, marking the first time these complex multipolarities have been tackled with bare nucleon charges and realistic nuclear interactions rather than effective parameters. Such predictive power represents a significant leap forward in theoretical nuclear physics, offering a window into the interplay of nuclear forces and quantum electrodynamics within the atomic nucleus.
The implications of this research extend well beyond ^53Fe. By establishing the validity of ab initio methods for describing the highest-multipole electromagnetic transitions, the study paves the way for future investigations of rare nuclear processes that have long eluded precise theoretical interpretation. These advancements could potentially inform our understanding of nuclear structure in exotic isotopes and guide experimental searches for new nuclear isomers with unusual decay properties, some of which might have applications in quantum information sciences or nuclear astrophysics.
From an experimental perspective, the ability to compute precise electromagnetic decay rates without adjustable parameters represents a paradigm shift. Traditionally, nuclear models often required phenomenological tuning to unify theory and experiment, but this study’s success with bare charges demonstrates a clean, first-principles approach. This not only improves the predictive accuracy for unmeasured nuclear states but also builds a stronger theoretical foundation for interpreting future experimental discoveries and designing new experiments with higher sensitivity.
Moreover, this work highlights the power of high-performance computing and algorithmic sophistication in tackling some of the most challenging problems in fundamental physics. The VS-IMSRG technique, combined with modern chiral nuclear forces, emerges as a versatile and highly accurate tool capable of addressing many unresolved questions concerning nuclear electromagnetic phenomena. It is anticipated that ongoing developments in computational physics will enable even larger nuclei and more intricate transitions to be studied in the near future, expanding the frontier of nuclear theoretical capabilities.
The team’s findings emphasize the remarkable uniqueness of ^53Fe’s E6 transition, an emblematic case of how nature’s quantum complexity produces extraordinary nuclear states. The hexacontatetrapole transition involving a single photon emission remains a rare jewel in the nuclear landscape—a process exquisitely sensitive to the microscopic details of nuclear structure and interactions. Through this research, scientists now have a robust theoretical framework to explore these phenomena with unprecedented precision and confidence.
Looking ahead, the ab initio framework demonstrated here could be extended to investigate other high-multipole electromagnetic transitions, some of which may play roles in astrophysical nucleosynthesis or serve as probes into exotic nuclear matter. Understanding such processes enriches our knowledge of elemental formation, nuclear stability, and the fundamental symmetries governing atomic nuclei. Furthermore, the ability to precisely model long-lived nuclear isomers may have practical implications for nuclear technology, including energy storage and radiation shielding.
The lead author of the study, Dr. Siqin Fan, expressed enthusiasm regarding the potential of the ab initio approach, noting that it eliminates the need for empirical effective charges that have historically complicated the theoretical description of nuclear electromagnetic transitions. A senior nuclear theorist involved in the project further underscored how this breakthrough offers new avenues for the exploration of nuclear structure, especially regarding rare and extreme transitions that challenge conventional nuclear models. These developments signify an exciting era in nuclear physics, where theory and computation are intersecting to reveal deeper layers of complexity within the atomic nucleus.
The complete study detailing these findings is published in the journal Nuclear Science and Techniques and can be accessed via DOI: 10.1007/s41365-025-01812-2. This seminal work is expected to stimulate further experimental and theoretical efforts to probe the frontiers of nuclear electromagnetic phenomena and to test the limits of our understanding of nuclear forces and configurations.
Subject of Research: Not applicable
Article Title: Ab initio calculations of the highest-multipole electromagnetic transition ever observed in nuclei
News Publication Date: 12-Sep-2025
Web References: http://dx.doi.org/10.1007/s41365-025-01812-2
Image Credits: Si-Qin Fan
Keywords
Nuclear physics, Electromagnetic spectrum, Isomerization
Tags: ab initio calculation of nuclear transitionsadvanced computational techniques in physicsangular momentum in nuclear transitionselectromagnetic transitions in nucleiexperimental analysis of nuclear phenomenahexacontatetrapole E6 transitionhigh-multipole electromagnetic decaysinsights into nuclear structure under extreme conditionsiron-53 nuclear physicsnuclear isomeric statesrare electromagnetic decays in isotopestheoretical frameworks in nuclear structure
