Radiative decay of the Th 229 m nuclear clock isomer in different host materials

A comparative vacuum ultraviolet spectroscopy study conducted at ISOLDE-CERN of the radiative decay of the Th 229 m nuclear clock isomer embedded in different host materials is reported. The ratio of the number of radiative decay photons and the number of Th 229 m embedded are determined for single crystalline CaF 2 , MgF 2 , LiSrAlF 6 , AlN, and amorphous SiO 2 . For the latter two materials, no radiative decay signal was observed and an upper limit of the ratio is reported. The radiative decay wavelength was determined in LiSrAlF 6 and CaF 2 , reducing its uncertainty by a factor of 2.5 relative to our previous measurement. This value is in agreement with the recently reported improved values from laser excitation.