The first ab initio calculation of the rarest electromagnetic transition in atomic nuclei, the hexacontatetrapole E6 transition in 53 Fe, has been performed. Using the valence-space in-medium similarity renormalization group (VS-IMSRG) methods with realistic nuclear force and bare nucleon charges, the study has successfully explained both the excitation energies and electromagnetic decay rates of the unique T 1/2 = 2.54-minutes J π = 19/2 - isomer at 3.0 MeV. This study provides unprecedented insights into nuclear structure under extreme conditions and validates ab initio approaches for describing the high-multipole electromagnetic transitions in atomic nuclei. The research demonstrates that the formation of 19/2 - isomer arises from the pure 0 f 7/2 orbital configuration.
Unique Nuclear Isomer Phenomenon
The J π =19/2 - isomer in 53 Fe represents an extraordinary nuclear phenomenon which can directly decay to the ground state with a single photon with angular momentum of 6 ℏ emitting. This E 6 transition is exceptionally rare in nature, while similar high-multipole processes have been observed in solid hydrogen and atomic rubidium, 53 m Fe remains the only nuclear system where such a high-multipole single-photon emission occurs spontaneously.
In a recently published paper, the research team employed the state-of-the-art VS-IMSRG technique with two different chiral nucleon-nucleon plus three-nucleon interactions. Unlike empirical models that require effective charges adjusted for different multipolarities, this approach uses bare nucleon charges consistently across all transition types.
Experimental Validation and Theoretical Implications
The calculations successfully reproduce the experimental excitation spectrum for the first time and provide the first ab initio calculations for the E 6, M 5, and E 4 transition probabilities. The ab initio method allows researches to calculate electromagnetic transitions without phenomenological adjustments. The results achieved convergence with large model spaces up to e max =14 and E 3max =24, providing reliable predictions for these extremely sensitive observables.
Scientific Significance and Future Applications
" The ab initio method allows us to calculate electromagnetic transitions without effective charges. " said the leader researcher of this work, Doctor Siqin Fan. " This work opens new avenues for understanding high-multipole transitions in nuclei," commented a senior nuclear theorist involved in the study. "The ability to describe such extreme transitions with bare charges represents a significant milestone in nuclear structure theory. "
The complete study is accessible by DOI: 10.1007/s41365-025-01812-2
Nuclear Science and Techniques
Computational simulation/modeling
Not applicable
Ab initio calculations of the highest-multipole electromagnetic transition ever observed in nuclei
12-Sep-2025