Nuclear clock

A nuclear clock or nuclear optical clock is an atomic clock being developed that will use the energy of a nuclear isomeric transition as its reference frequency, instead of the atomic electron transition energy used by conventional atomic clocks. Such a clock is expected to be more accurate than the best current atomic clocks by a factor of about 10, with an achievable accuracy approaching the 10⁻¹⁹ level.

The only nuclear state suitable for the development of a nuclear clock using existing technology is thorium-229m, an isomer of thorium-229 and the lowest-energy nuclear isomer known. With an energy of 8.355733554021(8) eV, this corresponds to a frequency of 2020407384335±2 kHz, or wavelength of 148.382182883 nm, in the vacuum ultraviolet region, making it accessible to laser excitation.