(a) Fit of EXAFS data and (b) its respective Fourier transform for radium sulphate (red line: model, black line: experimental data, green line: Ra–O contribution, dashed black line: Ra⋯S contribution, and blue line: residual). The EXAFS data are offset by 1.5 (cumulative) for each contribution. The residual should optimally be a straight line. In this case it is not, which means that there are interactions that are not accounted for in the model.