Synchrotron Mössbauer source: trade-off between intensity and linewidth

A synchrotron Mössbauer source (SMS) enables conventional (energy-domain) Mössbauer spectroscopy at synchrotron radiation facilities. In comparison with radioactive sources, SMS provides a beam of several micrometres in size, permitting studies of extremely small samples. The SMS linewidth can be narrowed at the expense of its intensity by varying the angular position and temperature of the key element of the SMS - an iron borate ⁵⁷FeBO₃ crystal. Here, in order to optimize the SMS performance, the angular and temperature dependencies of the SMS parameters have been studied and the optimal angular position and temperature of the crystal have been determined for highest intensity at specified source width. The results show that, when accepting broadening of the source width up to ∼6 natural widths, the intensity of the SMS at the European Synchrotron reaches more than 10⁵ γ-quanta s^-1. In the opposite extreme, the width of the source approaches the natural width with intensity decreasing to about 10³ γ-quanta s^-1. These changes of intensity up to two orders of magnitude take place over a temperature range of about 0.5°C. For all temperature and angular conditions, the instrumental function of the source was derived; we also analyzed the modification of its shape when passing from the `low-width' to `high-intensity' extremes of SMS operation. Finally, we estimated the influence of the temperature instability and mosaicity of the iron borate crystal on the SMS performance.