A laser worthy of a nuclear clock
The nucleus of the thorium-229 isotope has a special property: it has an excited state that's incredibly close in energy to its ground state. The existence of such an isomer is remarkable because…
thorium-229
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Clocks on the cusp of a nuclear age
You need three things to build a clock: an energy source, a resonator, and a counter. In an analog wrist watch, for example, a small battery is the energy source that sends a small electric signal to…