Michael Gennari

An ordinary atomic nucleus is like a tight ball: protons and neutrons are packed closely together. But some light nuclei, such as helium-6, are different. Two neutrons seem to step aside and form a dilute cloud around the nucleus — called a halo.

Imagine an hourglass where the sand grains transform into other grains as they fall: that's what unstable atomic nuclei are like. They live for an instant and then decay, ejecting an electron (this is beta decay). In September 2025, theorists and experimentalists gathered under the FRIB Theory Alliance to discuss how to use such decays to probe the structure of matter.