Physicists have made a groundbreaking discovery by examining the distribution of magnetism within a molecule’s nucleus, marking the first time this phenomenon has been observed. In a study published on October 23, 2023, in the journal Science, a team from CERN and MIT investigated a rare radioactive molecule known as radium monofluoride (RaF), revealing new insights into the complexities of nuclear magnetism.
The research aims to uncover fundamental asymmetries in nature. Physicists often rely on the concept of symmetry to understand the universe’s behavior. For instance, the same laws of gravity apply whether one drops a ball in Seattle or Tokyo. Yet, certain aspects of the universe do not conform to this ideal. A significant question remains: why does our universe predominantly consist of matter rather than equal parts matter and antimatter?
The study of radioactive nuclei presents a promising avenue for probing these asymmetries. According to Silviu-Marian Udrescu, a physicist at MIT and co-author of the study, the uneven arrangement of protons and neutrons in these nuclei can amplify subtle symmetry breaks, potentially leading to discoveries beyond the well-established Standard Model of particle physics.
Exploring RaF’s Unique Properties
The RaF molecule consists of two atoms: radium and fluoride. The radium nucleus exhibits a distinctive characteristic known as “octupole deformation,” which gives it an asymmetric shape, likened to that of a pear or an avocado. Shane Wilkins, the study’s first author, explained the significance of this shape, noting that such deformations occur in only a handful of atomic nuclei and are typically associated with radioactivity. This radioactivity complicates research, as these isotopes are unstable, decaying within approximately 15 days, and are challenging to produce in large quantities.
The team successfully created radium monofluoride at CERN’s ISOLDE facility, where they bombarded a uranium target with high-energy protons to generate the rare isotope radium-225. This isotope was then combined with fluorine gas, resulting in molecules that existed for mere fractions of a second. The researchers managed to detect only about fifty viable molecules per second for measurement.
To explore the magnetic properties of the RaF molecule, the researchers directed multiple laser beams of slightly varying frequencies at the molecules. By measuring the light absorbed or emitted during these interactions, they produced a spectrum that typically reveals information about electron behavior around the nucleus. In this case, however, the results indicated that the electrons were influenced by properties within the radium nucleus itself.
Significance of the Bohr-Weisskopf Effect
This internal influence is known as the Bohr-Weisskopf effect, which had not been observed in a molecular context until this study. Wilkins emphasized the importance of this finding, stating, “To the best of our knowledge, it’s never been seen in a molecule before.” The team successfully observed this effect experimentally and provided a theoretical explanation, showcasing the potential of these molecules for precision measurements.
With the internal structure of RaF mapped, the researchers can now aim to detect even smaller effects that may challenge established notions of symmetry in nature. The next phase of their research involves slowing and trapping these molecules using lasers to conduct more precise measurements, paving the way for future investigations into new physics.
Udrescu remarked on the potential of RaF molecules, stating, “Now we know they can be powerful tools to look for new physics.” This research not only advances our understanding of nuclear magnetism but also opens new avenues for studying the fundamental forces that shape our universe.