The orientation of apatite crystals in bone

In neutron‐diffraction measurements of the orientation of apatite crystals, for studying the stress distribution in bone, it is necessary to remove substantially the collagen in order to reduce the incoherent scattering. Data from X‐ray and neutron diffraction indicate the effect of chemical treatment with hydrazine and ethylenediamine and of heat treatment up to 650°C. Crystal growth commences above 500°C, with a slight sharpening of the curve of preferred orientation but without change of the preferred direction. Typically the half‐width at half‐intensity is reduced from 28° to 24° at 650 °C. Fortuitously, because of the differences of scattering amplitudes for the constituent atoms in apatite, the neutron pattern is much more informative concerning crystallinity than is the X‐ray pattern.