In research published on October 23 in Science, the team precisely measured the energy of electrons orbiting a radium atom that was chemically bound to a fluoride atom, forming radium monofluoride. By using the molecular environment as a microscopic stand-in for a particle collider, they confined the radium atom's electrons and increased the likelihood that some would briefly pass through the nucleus.

Traditional experiments that investigate nuclear interiors depend on kilometer-scale accelerators that speed up electron beams to smash into and fragment nuclei. The new molecule-centered approach provides a compact, table-top way to directly probe the inside of a nucleus.

Table-Top Method Detects Nuclear "Messages"
Working with radium monofluoride, the researchers tracked the energies of the radium atom's electrons as they moved within the molecule. They observed a small shift in energy and concluded that some electrons must have briefly entered the nucleus and interacted with what lies inside. As those electrons left, they retained the energy change, effectively carrying a nuclear "message" that reveals features of the nucleus's interior.

The method opens a path to measuring the nuclear "magnetic distribution." Inside a nucleus, each proton and neutron behaves like a tiny magnet, and their orientations depend on how these particles are arranged. The team plans to use the technique to map this property in radium for the first time, a step that could inform one of cosmology's central puzzles: why the universe contains far more matter than antimatter.

"Our results lay the groundwork for subsequent studies aiming to measure violations of fundamental symmetries at the nuclear level," says study co-author Ronald Fernando Garcia Ruiz, who is the Thomas A. Franck Associate Professor of Physics at MIT. "This could provide answers to some of the most pressing questions in modern physics."