Th-229 isomer detection via radiative decay of U-233 in the CaF2 environment

Abstract

Precisely measuring the wavelength of the 229Th isomer gamma photon is acrucial step in the development of a thorium nuclear clock [1]. In this researchproject, the radiative α decay of 233U was used to detect the 229Th isomer in the CaF2 crystal environment. For this purpose a 233U doped CaF2 crystal was grown and installed into a VUV spectrometer operating in the wavelength rangeof 120nm to 220 nm. The spectrometer was calibrated using the N2 lines at149.35nm and 174.40 nm, as well as the Xe line at 146.96 nm. The isomer was successfully detected and the wavelength was measured to be 150.37±1.31 nm.To reduce the error, more precise measurements and improved calibration efforts are still ongoing.