Okayama University team moves closer to creating ultraprecise 'nuclear clock'


A team including Okayama University scientists has said it took a major step toward creating a “nuclear clock” accurate to within one second in 300 billion years.

The team succeeded in producing a special state of atomic nuclei necessary to create a nuclear clock, according to a study published recently in the online edition of the British journal Nature.

Nuclear clocks, which would be far more precise than existing atomic clocks, are expected to be used not just for accurate timekeeping but also for uncovering the secrets of the universe’s accelerated expansion.

A cesium-based atomic clock, currently used to define a second, is accurate to within one second in tens of millions of years.

In the study, researchers including professor Koji Yoshimura of the university’s Research Institute for Interdisciplinary Science in Okayama, succeeded in putting thorium-229 nuclei in an excited state in which the nuclei have absorbed energy from outside.

The special state, called an isomeric state, was difficult to achieve, even though the nucleus of thorium-229, which is an isotope of thorium, a radioactive metal, is most easily excitable in the natural world.

The team irradiated thorium-229 nuclei with X-rays to make them transition to a state higher in energy than the desired isomeric state. The team then adjusted the X-ray energy to make about 60 percent of the nuclei decay to the desired state.

The irradiation experiment was conducted at the SPring-8 synchrotron radiation facility in Sayo, Hyogo Prefecture.

“We’ve taken a big step toward realizing a nuclear clock,” Yoshimura said.

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