In 2019, the isomer’s energy was measured via the detection of internal conversion electrons emitted in its direct ground-state decay to 8.28 ± 0.17 eV. Also a first successful excitation of the 29 keV nuclear excited state of Th via synchrotron radiation was reported, enabling a clock transition energy measurement of 8.30 ± 0.92 eV. In 2020, an energy of 8.10 ± 0.17 eV was obtained from precision gamma-ray spectroscopy.