The universe operates under a fundamental principle of symmetry—the laws of physics should apply equally across time and space. While this holds true for most phenomena, like gravity or electromagnetism, certain aspects of nature exhibit tiny imbalances that scientists are struggling to explain. One such mystery lies within radioactive nuclei. These atomic cores, with their uneven distribution of protons and neutrons, amplify even the faintest breaks in symmetry.
Scientists believe uncovering these asymmetries could lead to breakthroughs beyond our current understanding of physics, as described by the Standard Model. A team of researchers from CERN and MIT has taken a giant leap towards this goal. For the first time ever, they have observed how magnetism is distributed within the nucleus of a molecule—a feat previously impossible due to technical limitations.
A Unique Molecular Avocado
The key to this breakthrough lies in a specific radioactive molecule: radium monofluoride (RaF). This unusual compound consists of a radium atom bonded to a fluorine atom. The radium nucleus, known for its “octupole deformation,” possesses a distinct pear-like or avocado shape—a rare characteristic found in only a handful of atomic nuclei across the entire nuclear chart. This asymmetry makes RaF an ideal candidate for detecting subtle symmetry violations.
However, studying RaF presents significant challenges. Radium is notoriously radioactive, decaying rapidly within about 15 days. This instability means scientists can only produce minute quantities of the molecule and study it for fleeting moments. Each RaF molecule exists for mere fractions of a second before vanishing.
Unmasking Nuclear Magnetism
To overcome these hurdles, the researchers utilized CERN’s ISOLDE facility to generate radium-225 and combine it with fluorine gas. This process resulted in a continuous stream of barely detectable RaF molecules—only about fifty per second meeting the necessary conditions for measurement.
Employing highly precise laser beams tuned to specific frequencies, they bombarded these fleeting molecules. The absorption or emission of light by the molecule produced a spectrum—a unique fingerprint revealing information about the distribution of electrons surrounding the nucleus. In this case, however, unexpected shifts within the spectral patterns pointed towards something more profound: the influence of the radium nucleus’ internal magnetism on the orbiting electrons.
This phenomenon, known as the Bohr–Weisskopf effect, had previously been observed in individual atoms, where a single electron interacts with a single nucleus. Detecting it within a molecule was unprecedented due to the constant movement of electrons between the two nuclei in a molecule, which can obscure magnetic signals. But in RaF, the simpler fluorine atom allowed researchers to focus on the magnetic structure of the heavier radium nucleus.
A Window into New Physics?
This groundbreaking observation—a direct measurement of magnetism within a molecule’s nucleus—opens exciting new avenues for research. The team now plans to trap and slow down these molecules with lasers, enabling even more precise measurements that could reveal further tiny violations in symmetry. Such findings could point towards unknown particles or forces beyond the Standard Model, revolutionizing our understanding of the universe.
As Wilkins concludes, “Now we know they can be powerful tools to look for new physics.”
