The crystal structure of barium oxalate hydrate, BaC 2 0 4 3.5H20. was solved using synchrotron X-ray powder diffraction data, neutron powder diffraction data of BaC20-+ 3 SD20, and synchrotron X-ray single crystal diffraction data, measured on a microcrystal. The compound is monoclinic, g = 13.489(1), Q = 7.663(1). f = 15.085(1) A, B.= 113.569(5) 0• from the neutron data, space group ~2/f, No. 15, Z = 4. The precision of the structure arrived at with the syncJu·otron X-ray single crystal data is higher than that obtained with the neutron powder diffraction data. The barium atoms are bonded to the oxalate ions and to the water molecules with ten bmium oxygen bonds in the range 2.704(3) to 2.974(3) A. The structure has hydrogen bonds in the range 2.732 (4) Applications of anomalous dispersion in mate1ials science crystallography is a rapidly developing field, which has benefitted tremendously from the increasing availability and quality of X-ray synchrotron sources in the past decade. At the European Synchrotron Radiation Facility (ESRF). we have at the Mate1ials Science Bemnline recorded powder diffractograms of the zeolitic ionic conductor, tin mordenite, at 47 incident photon energies in the range from 29.008 keY to 29.708 keY, bracketing the Sn K-absorption edge at 29.2 ke V. The purpose of this study is to dete1mine the Sn atomic positions and the Sn-Sn interatomic distances which cannot be revealed by traditional crystallographic techniques clue to a disorder over several sites of the tin ions. (Knudsen. N .. Krogh-Andersen, E., K.roghAndersen, I. G., Norby, P., Skou. E. Solid St. Ionics. 61, (1993), 1 53). The sample also contains grains of tinoxide, Sn02. which complicates the analysis, and eliminates a nom1al EXAFS analysis as a possibility to determine interatomic distances. In order to solve the problem we use the newly developed diffraction anomalous fine structure (DAFS) technique. (Pickeiing, I. J., Sansone, M .• Mm·sch, J .. George, G. N. J. Am. Chem. Soc. 115, (1993), 6302. Stragier. H., Cross, J. 0., Rehr, J. J., Sorensen, L. B., Bouldin, C. E., Woicik, J. C. Phys. Rev. Lett. 69, (1992), 3064). This method in principle allows extraction of site-specific absorption spectra, so that despite crystallographic disorder and multiple phases, interatomic distances and valence states of the probe atoms can be cleteimined reliably. We will present the first results of this work.PS01.05.12 APPLICATIONS OF E:N""ERGY DISPERSIVE DIFFRACTION WITH SYNCHROTRON RADIATION. P. Suortti, V. Honkimaki, European Synchrotron Radiation Facility, B. P. 220, F-38043 Grenoble Cedex. FranceThe spectral b1ightness of a high-field wiggler at the ESRF bas been determined by using energy dispersive diffraction (EDD) from well-characteiized powder specimens. The results m·e in a close agreement with the brightness calculated from the emittm1ce of the elect:ron beam and the measured magnetic field of the wiggler. The precisely known brightness of the synclu·ot.ron beam can be used in many different studies with EDD. In the case of...