Andrey Surzhykov

The thorium nucleus with a mass number A = 229 attracts currently much interest because of its extremely low-lying first excited state. The existence of this nuclear isomeric state with excitation energy of about 8 eV opens the possibility for the development of a nuclear clock. Both the exact energy of the isomeric state as well as its nuclear magnetic dipole and electric quadrupole momenta are subjects of intense research. The latter can be determined by investigating the hyperfine structure of thorium atoms or ions. In this contribution we will discuss recent combined experimental and theoretical investigation of the hyperfine structure of the doubly ionized Th ion. We will see how the detailed analysis of the hyperfine structure allows one to extract accurate values of the nuclear momenta of the thorium isomeric state.