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

A comparative vacuum ultraviolet spectroscopy study conducted at ISOLDE-CERN of the radiative decay of the Th229m nuclear clock isomer embedded in different host materials is reported. The ratio of the number of radiative decay photons and the number of Th229m embedded are determined for single crystalline CaF2, MgF2, LiSrAlF6, AlN, and amorphous SiO2. 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 LiSrAlF6 and CaF2, 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.