Size effect of powdered sample on EXAFS amplitude

Powdered samples samples are commonly used to measure the extended X-ray absorption fine structure (EXAFS) and near-edge structure. It is shown that sizes of particles typically employed produce significant reduction in the EXAFS amplitude for concentrated samples. The distortion is calculated and found to be in good agreement with measurements on FeSi2 samples. To obtain accurate EXAFS amplitudes on powdered samples it is necessary to use particles significantly smaller than 400 mesh when the atom of interest is concentrated.