Th-229 Nuclear Clock Isomer: VUV Spectroscopy Studies

by Prof. Piet Van Duppen (KU Leuven)

Wednesday 22 May 2024, 11:15 → 12:45 Europe/Zurich

Ecole de physique

The thorium-229 nucleus contains an isomeric state with a low excitation energy, making it accessible to laser excitation. This makes it an ideal candidate for the development of a nuclear clock [1] which will enable testing fundamental principles in physics, such as e.g. potential variations of fundamental constants. Moreover, practical applications like relativistic geodesy might become possible [2]. 

The radiative decay of the thorium-229 isomer was observed for the first time at ISOLDE - CERN by populating it via the beta decay of actinium-229, implanting its shorterlived decay precursors in large bandgap crystals and observing the isomer’s VUV photons in a dedicated spectrometer. A reduced uncertainty of the isomer’s excitation energy (8.338 ± 0.024 eV) and a first determination of the isomer’s half-life (670 ± 102 s) in MgF2 was reported [3]. With the thorium-229 signal confirmed, a comparative study using different crystal materials, like SiO2, AlN, and LiSrAlF6, was performed in a recent campaign at ISOLDE, in addition to two new CaF2 thin-film crystals grown at different temperatures. With an improved calibration method, the wavelength of the isomer radiative decay was determined with better precision and the relative efficiency of vacuum-ultraviolet light from the different crystals was determined. Based on the results of these campaigns, population of the Th-229 isomer using laser excitation was very recently achieved, improving the precision on its energy value by several orders of magnitude [4].

In this seminar the new methodology, the results from the two campaigns and the prospects will be presented. 

References 

[1] E. Peik and C. Tamm, EPL 61, 181 (2003). 

[2] E. Peik et al., Quantum Sci. Technol. 6, 034002 (2021). 

[3] S. Kraemer et al., Nature 617, 706–710 (2023). 

[4] J. Tiedau et al., Physical Review Letters 132 (2024) 182501

Piet_Van_Duppen_2024_05_Geneva.pdf