Establishing 181Ta synchrotron Mössbauer spectroscopy

The goal of this proposal is to extend synchrotron Mössbauer spectroscopy (SMS) to other isotopes than 57Fe, here to the 6.2 keV resonance of 181Ta. SMS has been successfully established at the ESRF for the 14.4 keV nuclear resonance of 57Fe using the pure nuclear reflection from a perfect single crystal of 57FeBO3 to provide an energy-tunable single line to record 57Fe Mössbauer spectra. However, the unique mechanism of energy selection in the 57FeBO3 crystal is not applicable to other Mössbauer isotopes. We introduce here a novel concept to generate a tunable, single Mössbauer resonance line at 6.2 keV that is based on high-purity polarization filtering via two linear x-ray polarizers in a crossed setting. This concept can be applied to any Mössbauer resonance in the energy range between 5 and 30 keV. This technique will be highly promising, e.g., for research on materials for superconducting qubits, wherein the use of Ta increases their coherence time by 2 -3 orders of magnitude.