In spite of recent progress, the isomer’s radiative decay, a key ingredient for the development of a nuclear clock, remained unobserved. The isomer’s excitation energy, nuclear spin and electromagnetic moments, the electron conversion lifetime and a refined energy of the isomer have been measured 12, 13, 14, 15, 16. Whereas indirect experimental evidence for the existence of such an extraordinary nuclear state is substantially older 10, the proof of existence has been delivered only recently by observing the isomer’s electron conversion decay 11.

This nuclear clock will be a unique tool for precise tests of fundamental physics 4, 5, 6, 7, 8, 9. It constitutes one of the leading candidates for use in next-generation optical clocks 1, 2, 3. The radionuclide thorium-229 features an isomer with an exceptionally low excitation energy that enables direct laser manipulation of nuclear states. Nature volume 617, pages 706–710 ( 2023) Cite this article Observation of the radiative decay of the 229Th nuclear clock isomer

Half life blue shift guide