J. A. Sheikh

A bell doesn't ring with a single note — after being struck, it sounds with several harmonics at once. An atomic nucleus vibrates in much the same way: after a collision, it can oscillate, and these oscillations show up in the emitted gamma rays.

The atomic nucleus isn't a frozen ball but a seething collective of protons and neutrons. They whirl, collide, and arrange themselves into patterns that physicists see as "bands"—ladders of energy levels. In niobium and technetium nuclei, four such ladders have been found, but the last one stubbornly refused to fit the calculations.