Nature, Published online: 18 December 2024; doi:10.1038/d41586-024-04125-3

A rare isotope, thorium-229, exhibits a unique low-energy nuclear transition that could form the basis of a precise nuclear clock. Observation of this transition in vapour-deposited thin films, which require only minuscule amounts of 229Th, opens up a possible route to the widespread use of portable nuclear clocks.