MAGIC-ANGLE THEOREM IN POWDER X-RAY-ABSORPTION SPECTROSCOPY

We demonstrate that texture effects can seriously distort the measurement of x-ray-absorption data from powdered specimens. We show that the isotropic average dipolar x-ray-absorption spectrum can always be measured irrespective of the degree of texture, provided axial symmetry in the particle distribution function exists normal to the specimen surface and a linearly polarized x-ray beam is employed. A simple modification to synchrotron-radiation experiments to achieve this consists of rotating the specimen by m about an axis perpendicular to the polarization vector and beam direction from normal incidence. m is given by sin2 m=1/3. © 1990 The American Physical Society.