Towards a measurement of the nuclear clock transition in Th-229

We investigate a potential candidate for a future optical clock: the nucleus of the isotope ²²⁹Th. Over the past 40 years of research, various experiments have found evidence for the existence of an isomeric state at an energy of a few eV. So far, neither the energy nor the lifetime of the isomer have been determined directly. As the scene is not yet prepared for direct laser excitation, other means of populating the isomer need to be explored. We investigate three different approaches, all of which rely on CaF₂ crystals doped with ²²⁹Th or ²³³U. Various kinds of crystal luminescence are discussed in detail.