Towards a precise energy determination of the ²²⁹Th nuclear clock transition

The first isomeric excited nuclear state of ²²⁹Th (denoted with ^229mTh) exhibits the lowest excitation energy in nuclear physics which has been measured indirectly to be 7.8(5) eV. The uniquely low transition energy which corresponds to a wavelength of approximately 160 nm makes it possible to drive the transition with lasers. This in turn may pave the way for a long list of interesting applications (such as a nuclear optical clock) which has so far been hindered by the rather large uncertainty in the reported energy value. In this talk an experimental scheme is presented that uses internal conversion electrons which are emitted in the ground-state decay of ^229mTh and first results are shown. With these measurements a precise and direct determination of the excitation energy is in reach.