Intensities of Mössbauer diffractions from polycrystalline bcc57Fe

Abstract

Diffraction patterns were measured on a polycrystalline bcc 57 Fe foil using a Mössbauer powder diffractometer with high sensitivity. Measurements with and without a magnetic field normal to the scattering plane showed large differences in the diffracted intensities of the different nuclear resonances. These magnetic effects on diffraction intensities were interpreted successfully with a single scattering theory developed to handle isotropic and anisotropic orientation distributions of hyperfine magnetic fields. When there is coherent interference between nuclear scattering and x-ray Rayleigh scattering, an asymmetry in the coherent intensity of the three pairs of diffractions for the 57 Fe magnetic sextet ͑1,6͒, ͑2,5͒, ͑3,4͒ is predicted. This is largest in the presence of a uniaxial magnetic field, and the calculated and measured asymmetries were in good agreement. A reduced diffraction intensity for lines ͑2,5͒ and ͑3,4͒ caused by spin-flip incoherence was also measured. The effects of dynamical diffraction, if present, are shown to be small.

Site-specific long-range order in57Fe3Al measured by Mössbauer diffractometry

“…Figure 6 shows the measured energy spectra of the fundamental (211) Bragg diffractions. The experimental spectrum is shown at the top of figure 6 with calculated results obtained with kinematic theory, using scattering factors equivalent to equation (1), but without the multislice method (more details on these kinematic calculations have been given by Lin et al (2001) and Kriplani et al (2002) and in } 6.1). The energy spectrum calculated with the kinematic theory agrees well with the experimental data.…”

“…Stephens and Fultz (1997) first showed how 57 Fe atoms with specific chemical environments could be selected for diffraction by tuning the energy of the g-ray photons. Kriplani et al (2002) measured the angular dependence of diffraction intensity from polycrystalline bcc 57 Fe at various resonance energies. They found good agreement between experimental data and calculations by kinematic theory.…”

Spatial periodicities of defect environments in 57Fe3Al studied by Mössbauer powder diffractometry

“…The Mössbauer powder diffractometer consisted of a Bruker X-1000 Xe-filled area detector, a GE XRD-5 goniometer, a 57 Co (Rh) radioactive source, a Wissel Doppler drive system with laser interferometer velocity calibrator, and a control computer. This instrument was described recently [8,10,18]. All Mössbauer diffraction patterns were normalized to incident flux, with units of counts/sr/(mCi Á hour).…”

“…With this chemical selectivity, the spatial periodicities of 57 Fe atoms in different chemical environments can be determined from the energydependence of the nuclear Bragg diffractions. The measurements are enabled by developments in both the theory and practice of Mössbauer powder diffractometry, many of which occurred in the past decade [1][2][3][4][5][6][7][8][9][10].…”