The observation of the VUV signal from the isomeric state of 229 thorium nuclei toward realizing the atomic clock

Toward the nuclear clock’s realization, the problem of ambiguity of isomeric energy and its lifetime must be overcome by experimental measurement of de-excitation from the isomeric state of thorium-229 nuclei with emitting photons.

In our experiment, the thorium-229 nuclei are excited to an isomeric state via the 2nd excited level(29 keV) by irradiation of X-ray as synchrotron radiation from SPring-8. A dedicated measurement system captures the decay events in which the isomeric thorium nucleus emits photons within the VUV region. Finally, we have demonstrated the measurement of the VUV signal and determined both isomeric energy and lifetime. In our presentation, the current status and recent results would be reported.