Thorium 3300 has the smallest excitation energy among more than 229 kinds of atomic nuclei existing in nature.The excited state of thorium 229 is called the isomer state, which is the only nuclear excited state that can be excited using a laser.However, the conventional means for generating an isomer state is a complicated process involving radiation, and the accurate energy information necessary for realizing laser excitation has not yet been obtained.

　Under these circumstances, the researchers have made it possible to freely generate a large amount of isomer states by using the nuclear resonance scattering technology using high-intensity X-rays at the large-scale radiation facility (SPring-8).The ground state thorium 229 was irradiated with X-rays to excite it in the second excited state, and the transition to the isomer was observed using nuclear resonance scattering and a high-precision X-ray absolute energy monitor.It has the advantage of being able to generate isomers in a clean environment with little radiation, and by successfully generating isomers in a controlled state, the energy and lifetime of the second excited state, and from the second excited state to the isomer. It was said that it was possible to accurately determine the transition probability, etc., and it was possible to significantly advance the understanding of the thorium 229 nucleus.

　Thorium 229 is expected to be useful as a stage (platform) for the construction of ultra-precise "nuclear clocks", the search for dark matter, and the search for changes in physical constants over time.It is expected that this result will advance the research of isomer states and make great progress toward the realization of these.

Paper information:[Nature] X-ray pumping of the 229Th nuclear clock isomer