Electronic level structure investigations in Th+ in the energy range of the 229Th isomer

Among all known isotopes, 229Th possesses a uniquely low-lying nuclear excitation state at (7.8 ± 0.5) with an unperturbed lifetime of several 1000s. Since this energy corresponds to a wavelength in the vacuum-UV region of around 160 nm, direct laser excitation of the isomer is challenging. In the context of the search for the isomer transition in 229Th+, the excitation of the nuclear isomer is attempted by NEET (Nuclear Excitation by Electron Transition) processes in a two-step laser excitation via the electron shell.