Uncertainty budget for determinations of mean isomer shift from Mössbauer spectra

The magnetite/maghemite content within iron oxide nanoparticles can be determined using the mean isomer shift (δ¯$\overline {\delta }$). However, accurate characterisation of the composition is limited by the uncertainty associated with δ¯$\overline {\delta }$. We have identified four independent sources of uncertainty and developed a quantitative expression for the uncertainty budget. Sources of uncertainty are categorised as follows: that from the fitting of the Mössbauer spectrum (σfit), that of the calibration of the α-Fe reference spectrum (σcal), thermal corrections to the spectrum due to second order Doppler shift (SODS) (σΔδ) and other experimental errors (σerr). Each contribution is discussed in detail using 57Fe Mössbauer spectra obtained from an iron oxide nanoparticle system at temperatures between 16 K and 295 K on different spectrometers in two different laboratories.