A method for determining the transition energies of $$^{\mathrm {83m}}$$ Kr at the KATRIN experiment

The neutrino mass experiment KATRIN uses conversion electrons from the 32.2-keV transition of the nuclear isomer $$^{\mathrm {83m}}$$ Kr for calibration. Comparing the measured energies to the appropriate literature values allows for an independent evaluation of the energy scale, but the uncertainties in some of the literature values obtained by gamma spectroscopy are a limiting factor. Building upon the already excellent linearity of KATRIN’s energy scale, this paper proposes a novel method for determining the $$^{\mathrm {83m}}$$ Kr transition energies via high-precision electron spectroscopy. Notably, the method makes use of conversion electrons from the 41.6-keV direct transition of $$^{\mathrm {83m}}$$ Kr to its ground state in addition to conversion electrons from the much more frequent cascade of a 32.2-keV and a 9.4-keV transition. By implementing this method, KATRIN may be able to deliver order-of-magnitude improvements in precision over current $$^{\mathrm {83m}}$$ Kr transition energy literature values. Although concretely described here in the context of the KATRIN experiment and with $$^{\mathrm {83m}}$$ Kr, the method’s underlying principles are general enough for it to likely be a useful tool in various other nuclear spectroscopy settings.