Nuclear Clock: Nature publication on first realization of conversion electron Moessbauer spectroscopy in 229mTh

In a collaborative experimental effort, led by the team of Prof. Eric Hudson at the Unversity of California at Los Angeles, for the first time the excitation of the uniquely low-lying nuclear clock isomer in ²²⁹Th was achieved via conversion electron (Moessbauer-like) spectroscopy from a thin ²²⁹ThO₂ film. Contrary to the so far only successful technique to excite the thorium isomer via VUV excitation in large-bandgap, VUV transparent crystals, here VUV laser light was sent to an opaque material to excite nuclei near the surface, and then, instead of emitting photons like they do in transparent material such as the crystals, they emit electrons which can be detected simply by monitoring an electrical current.

The international research team included physicists from the Ludwig-Maximilians-Universität München, University of Manchester, University of Nevada Reno, Los Alamos National Laboratory, Ziegler Analytics, Johannes Gutenberg-Universität at Mainz.

Further details can be found in the Nature publication: R. Elwell et al., Nature 648, 300 (2025)