What Do Unstable Atomic Nuclei Look Like?

S ince the pioneering measurements of Robert Hofstadter and co-workers in the 1950s, it has been known that atomic nuclei are not point-like particles but have a finite size on the femtometer scale—about 10,000 times smaller than the atomic radius [1]. That Nobel Prize winning research revealed the internal structures and distinct spatial electric charge distributions of nuclei by directing high-energy beams of electrons from an accelerator toward the target materials and examining the directions in which the electrons were deflected. At the RIKEN Nishina Center for Accelerator-Based Science in Japan researchers have, for the first time, observed such electron scattering from radioisotopes that do not occur