Unveiling the secrets of the atomic nucleus, a groundbreaking method has emerged, allowing scientists to peer into the heart of an atom. A team, led by MIT researchers, has developed an innovative approach, utilizing a simple molecule to unlock the mysteries within a radium atom's nucleus.
In a recent study, the team observed electrons in radium monofluoride, detecting subtle energy changes that provide insights into the nucleus's core. This achievement was accomplished at CERN in Switzerland, not within the vast colliders, showcasing a practical method to explore nuclear structure and unravel the universe's preference for matter over antimatter.
Radium monofluoride acts as a key to atomic secrets. Molecules enhance the internal electric fields perceived by electrons, making rare effects more observable. The experiment, guided by Ronald Fernando Garcia Ruiz from MIT, was conducted at CERN's Collinear Resonance Ionization Spectroscopy facility.
Within radium monofluoride, the team tracked shifts in the molecule's hyperfine structure, tiny energy variations resulting from nucleus-electron interactions. These shifts serve as a unique signature of the nucleus, revealing its inner workings when electrons briefly interact with it.
Previous research highlighted radium monofluoride's unusual sensitivity to the nucleus's size, suggesting that electrons within this molecule can unveil hidden details.
"We've proven that we can sample the nucleus's interior," said Ronald Fernando Garcia Ruiz, emphasizing the significance of this claim, which is supported by precise measurements and rigorous cross-checks.
The team paired radium with fluoride, cooling and trapping the molecules before probing their electron energies with lasers. Their findings revealed a small but distinct deviation from theoretical predictions, indicating that electrons spend a fraction of their time within the nucleus.
This new data provides insights into the nuclear magnetization distribution, detailing how magnetism is distributed within the nucleus. This property influences the hyperfine pattern, which advanced theory can calculate and experiments can test.
A 2020 analysis emphasized the importance of modeling this distribution for heavy systems like radium and its molecules. The present measurements validate this concept, transforming theoretical calculations into experimental benchmarks.
Radium 225 exhibits a rare symmetry, with an octupole deformed nucleus, giving it a pear-shaped nuclear structure. This asymmetry amplifies certain symmetry-breaking effects, which are almost imperceptible in ordinary nuclei.
Physicists are intrigued by these effects as they relate to time reversal and charge parity violations, which may explain matter's dominance over antimatter in the universe.
"The radium nucleus is predicted to amplify this symmetry breaking due to its asymmetric charge and mass distribution, which is quite unusual," explained Ruiz, justifying the team's choice of radium as the molecule's core.
A 2024 overview by the U.S. Department of Energy highlights the value of short-lived radioactive molecules for such investigations, combining nuclear mass with laser control in a unique way.
This new method offers an alternative to traditional nuclear scattering, which uses electron beams and detectors spread across large facilities. While those experiments provide valuable insights, they are costly and infrequent.
The molecule-based approach reads nuclear information from the light emitted or absorbed by trapped molecules, trading brute force for precision. It operates on a tabletop scale, utilizing lasers and vacuum chambers.
Despite the challenges, including the scarcity and radioactivity of radium and the rapid decay of radium monofluoride, the team successfully extracted a clear signal. They observed a pattern consistent with electrons briefly interacting with the nuclear interior, resulting in measurable energy shifts.
The next step is to map the magnetism distribution across the radium nucleus, requiring the alignment and cooling of molecules to reduce thermal motion. These maps will enhance the theory used to predict symmetry violation signals and help set tighter limits on quantities related to an electric dipole moment.
If future experiments detect hints of symmetry breaking, it could challenge parts of the Standard Model, the current theory of fundamental particles. Even a null result provides valuable information, narrowing the possibilities for new physics.
Radium monofluoride opens a new perspective, but skeptics may question if stray fields or modeling choices could mimic the observed shift. The team addressed this by comparing multiple transitions and using calculations that account for relativistic and electron correlation effects.
It's also reasonable to ask if this approach can be applied beyond radium monofluoride. Ongoing research explores other heavy molecules with similar features, and several groups are developing complementary techniques.
The impact extends beyond theory validation, offering a compact method to study nuclear structure that could expand access beyond a few giant labs.
While the method will evolve, the core message remains: molecules can carry information from within the nucleus to a detector, and precise measurements can decipher this information.
The study is published in Science, providing a significant contribution to the field of nuclear physics.
