An atomic nucleus that gains extra energy usually emits it as light. But there's another path, discovered by Lise Meitner: the nucleus kicks out one of its own electrons — a process called internal conversion. In a solid, the runaway electron becomes the main way to shed energy.

The thorium-229 nucleus is special: its excited state lies almost at the very bottom, like a whisper on the edge of silence. This energy is only enough for a faint ultraviolet flash, so the nucleus's fate depends entirely on its electronic surroundings. Calculations from a computer model of a ThO₂ crystal showed that a narrow "energy ditch" between bands speeds up conversion to microseconds, while a wide one stretches it out hundreds of times. By changing the material, we can control this process, adjusting the ditch's depth.

This controlled delay turns the crystal into a nuclear clock. It will serve as a quantum measurer for hunting dark matter and testing the Standard Model. Unlike ordinary clocks, these could sense gravitational time dilation when going up a couple of floors, just embed them into a quantum sensor.