DYNAMICAL DIFFRACTION AND X-RAY STANDING WAVES FROM 2-FOLD REFLECTIONS IN THE QUASICRYSTAL AlPdMn Terrence Jach, National Institute of Standards and Technology, S. M. Thurgate, Murdoch U., Australia, Yi Zhang, R. Colella, Purdue U., S. Kycia, Cornell U., A. I. Goldman, Iowa State U., M. de Boissieu, M. Boudard, LTPCM/ENSEEG, France.

We have observed x-ray diffraction from the (420024) and (640046) reflections of an AlPdMn quasicrystal in the back-reflection Bragg geometry [[theta]]_B=90deg.. The rocking curves observed by scanning the energy of the synchrotron radiation possess widths close to the Darwin width expected in a dynamical theory. As a result, observation of the K[[alpha]] fluorescence from the Al and the L[[alpha]] fluorescence from the Pd atoms exhibits strong x-ray standing wave behavior, similar to that observed in crystalline materials. The data suggest a long range order of ''quasiplanes'' of specific elements, as seen by a ''coherent position'' which differs for the x-ray fluorescence from the Al and Pd atoms.