THE MOSSBAUER EFFECT OF FE57 ON THE SURFACE OF TUNGSTEN.
Technical note no. 2,
ILLINOIS UNIV URBANA
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The Mossbauer effect of Fe57 on the surface of polycrystalline tungsten was measured over a temperature range of 80 - 500K, and at angles of 0 degrees and 60 degrees with respect to the normal. The Mossbauer spectra consist of three unresolved lines, the middle one agreeing with measured spectra of Fe57 in the bulk of tungsten, and the outer two being attributed to surface effects. The assymmetry of the surface spectra, the angular dependence of the shape, and the magnitude of the splitting of the two surface lines indicate an electric field gradient at the surface of 2.4 x 10 to the 16th power Vsq cm directed along the normal. An effective Debye temperature of 406 12K is found for the bulk, from a study of the temperature dependence of the intensity of the Mossbauer absorption. The effective Debye temperature for the surface is 354 30K along the normal, and 255 30K parallel to the surface. The angular dependence of the total intensity of the two surface lines agrees with a simple theory for an atom bound above the top layer of the host lattice. The isomer shift with respect to iron at 300K is .0151 .0002 cmsec in the bulk, and .018 .002 cmsec on the surface. Author