Physicists at the Massachusetts Institute of Technology (MIT) have pioneered an innovative method to probe the intricate inner structure of atomic nuclei by harnessing the intrinsic properties of electrons within molecules. This groundbreaking research leverages the unique behavior of electrons in molecules containing radium atoms, revealing minute energy shifts that serve as direct evidence of electrons momentarily penetrating the nucleus. The study, featured in the journal Science, marks a significant leap forward in our capacity to explore nuclear properties without relying on large-scale particle accelerators, instead employing table-top experimental setups that exploit molecular environments.
At the heart of this novel technique is the molecule radium monofluoride (RaF), which pairs a radium atom with a fluoride atom. This molecular system acts as a microscopic laboratory where the electrons surrounding the radium nucleus experience extreme electric fields, intensifying their interaction with the nucleus itself. Electrons typically orbit nuclei at a distance where interactions occur outside the nuclear boundary, but in this molecule, some electrons gain a probability to briefly penetrate the nucleus, interacting directly with its protons and neutrons. This brief intrusion leaves a quantifiable imprint on the electron’s energy—a subtle shift revealing the ‘message’ from the nuclear interior.
Traditionally, the exploration of nuclear structure has necessitated vast accelerator facilities that propel electrons to near-light speeds, colliding them with nuclei to break them apart and study their constituents. Such experiments are not only resource-intensive but limited in the atomic species they can probe effectively. MIT’s molecular approach circumvents these challenges by using naturally occurring molecular electric fields as powerful confinement and amplification factors, enabling precise measurement of electron energy levels with extraordinary sensitivity. This refinement opens a pathway to studying rare and radioactive isotopes like radium, which pose production and handling challenges.
The significance of probing radium nuclei stems from their unusual shape and properties. Unlike most nuclei, which exhibit roughly spherical configurations, radium’s nucleus is pear-shaped—an asymmetry that profoundly influences its internal magnetic distribution and the alignment of its constituent nucleons. This deformation enhances the nucleus’s sensitivity to violations of fundamental symmetries in physics, such as parity and time-reversal invariance, which are critical to understanding the predominance of matter over antimatter in the universe. Understanding these violations has been a longstanding mystery and requires exquisitely sensitive experimental methodologies such as the one devised by the MIT team.
In the experimental setup, the researchers cooled and trapped RaF molecules within vacuum chambers, using carefully calibrated lasers to induce transitions and measure energy states of the electrons with atomic-scale precision. This laser spectroscopy enabled the detection of an energy deviation as slight as one part per million relative to the photon energy—indicative of electrons accessing and interacting with nuclear material. These results provide compelling evidence that electron-nucleus penetration occurs and that electrons carry back information about the nuclear interior, effectively turning them into messengers that communicate nuclear features via their energy shifts.
This capacity to sample inside the nucleus through electron behavior represents a breakthrough analogous to measuring the electric field inside a battery, rather than just outside it. It expands the realm of nuclear spectroscopy by adding a dimension of intranuclear sensitivity that was previously unattainable without massive experimental installations. The team’s findings therefore lay a solid foundation for future investigations aiming to precisely map nuclear magnetization distributions and explore fundamental symmetry violations at the nuclear scale, providing fertile ground for advances in both nuclear physics and cosmology.
One of the key goals arising from this research is to exploit the radium nucleus’s pear shape for enhanced detection of symmetry-violating phenomena. Because the shape amplifies electric dipole moments that violate time-reversal symmetry, it offers an exceptional natural laboratory to detect possible physics beyond the Standard Model. By further controlling molecular orientations and cooling techniques, researchers aim to isolate nuclear alignments and enhance measurement precision, potentially observing effects that have eluded detection for decades and shedding light on why the observable universe is dominated by matter.
Radium poses experimental challenges due to its radioactivity and the difficulty in producing sufficient quantities of radium-containing molecules. The team’s success in detecting electron penetration signals within tiny populations of RaF molecules underscores the extraordinary sensitivity of their molecular trap and measurement approach. It demonstrates that even sparsely available isotopes can be investigated effectively, opening possibilities for the study of other rare or unstable nuclei previously inaccessible to detailed spectroscopic scrutiny.
Moreover, these experiments engage with broader questions in fundamental physics, particularly the search for additional sources of symmetry violation required to explain the matter-antimatter asymmetry in the cosmos. Confirming these violations at the nuclear level could alter our understanding of particle physics and the laws governing the universe’s evolution. The molecular method’s fine-scale probing capability places it at the forefront of such investigations, bridging atomic, nuclear, and particle physics in a single platform.
The collaborative efforts that facilitated this breakthrough span several leading institutions, including CERN’s Collinear Resonance Ionization Spectroscopy Experiment (CRIS), where the radium isotopes were produced and preliminary measurements conducted. This international partnership underscores how modern nuclear physics research increasingly relies on inter-institutional expertise and resources, fostering advances that no single facility could achieve alone. The integration of molecular physics techniques with nuclear spectroscopy exemplifies the multidisciplinary innovation driving progress in fundamental science.
Looking forward, the MIT team envisions enhancing control over molecular systems by reducing thermal motion and orienting the pear-shaped nuclei within radium monofluoride, thereby enabling detailed spatial mapping of nuclear magnetization. Such advancements would allow researchers not only to gauge the distribution of nuclear forces but also to detect minute deviations from expected symmetrical properties, clues that may signal entirely new physics. The continuous refinement of these molecular probes promises to transform our capacity to interrogate the nucleus, turning molecules into unprecedented windows revealing the core of matter.
In sum, this pioneering study offers a paradigm shift in nuclear exploration, utilizing electrons as internal messengers within molecular environments to access and decode the properties of atomic nuclei. It combines high-precision laser spectroscopy, advanced molecular trapping, and the quantum mechanical peculiarities of heavy atoms like radium to reveal nuclear secrets that underpin both the fabric of matter and the fundamental asymmetries shaping our universe. As research progresses, this approach holds tremendous potential for breakthroughs that could ripple across physics, chemistry, and cosmology alike.
Subject of Research:
Probing nuclear structure and symmetry violations within radium nuclei using electron energy shifts in radium monofluoride molecules.
Article Title:
Observation of the distribution of nuclear magnetization in a molecule
News Publication Date:
23-Oct-2025
Web References:
DOI: 10.1126/science.adm7717
Image Credits:
Courtesy of Ronald Fernando Garcia Ruiz, Shane Wilkins, Silviu-Marian Udrescu, et al
Keywords
Atomic physics, Nuclear magnetization, Radium nucleus, Molecular spectroscopy, Symmetry violation, Matter-antimatter asymmetry, Pear-shaped nucleus, Radium monofluoride, Electron penetration, Fundamental symmetries, Particle physics, Laser spectroscopy
Tags: advancements in nuclear physics researchatomic nuclei researchelectron behavior in moleculesenergy shifts in atomic nucleiinnovative probing techniquesmicroscopic laboratory techniquesMIT physicists breakthroughmolecule-based nuclear explorationnuclear interactions with electronsnuclear properties without particle acceleratorsradium monofluoride applicationstable-top experimental setups
