Energy of the ²²⁹Th nuclear clock transition

Area of Science:

• Nuclear Physics
• Atomic Physics
• Metrology

Background:

• The first excited isomeric state of thorium-229 (229mTh) is a promising candidate for a nuclear optical clock due to its low excitation energy and long radiative lifetime.
• Development of a nuclear clock, with applications in geodesy and fundamental constant research, has been hindered by imprecise knowledge of the 229mTh energy.
• Current atomic clocks based on electronic shells have limitations that nuclear clocks aim to overcome.

Purpose of the Study:

• To directly measure the transition energy of the 229mTh isomeric state to its ground state with high precision.
• To determine the wavelength corresponding to this nuclear transition for laser spectroscopy applications.
• To advance precision metrology and enable the development of an accurate nuclear optical clock.

Main Methods:

• Spectroscopy of internal conversion electrons emitted during the decay of neutral 229mTh atoms.
• Direct measurement of the transition energy with an uncertainty of 0.17 electronvolts.
• Calculation of the transition wavelength using the measured energy.

Main Results:

• The transition energy of 229mTh to the ground state was measured with a standard deviation uncertainty of 0.17 eV.
• The energy corresponds to a transition wavelength of 149.7 ± 3.1 nanometers.
• This wavelength is accessible via laser spectroscopy using high-harmonic generation.

Conclusions:

• The precise measurement of the 229mTh transition energy facilitates high-resolution laser spectroscopy on nuclei.
• The findings are a critical step towards the development of a nuclear optical clock with unprecedented accuracy.
• This research combines nuclear and atomic physics to significantly advance precision metrology.