The 2θ determination of diffraction peaks from `poor' powder samples. Application to biological apatite

A method is presented for improving the accuracy of the determination of peak positions from step-scanned X-ray powder diffraction data. This method is intended to be used in situations where the nature of the sample produces broad asymmetric peaks with a low peak-to-background ratio. A Fourier series is fitted to the experimental step-scan observations and the peak position is calculated from this functional representation. The method has been tried on the mineral apatite from biological sources, mainly bone, where ionic substitutions affect the cell parameters.