International
Tables for Crystallography Volume H Powder diffraction Edited by C. J. Gilmore, J. A. Kaduk and H. Schenk © International Union of Crystallography 2018 |
International Tables for Crystallography (2018). Vol. H, ch. 3.6, p. 291
Section 3.6.2.6.2. Source emission profile^{a}Department of Civil, Environmental and Mechanical Engineering, University of Trento, via Mesiano 77, 38123 Trento, Italy |
For X-rays, the source emission profile at an energy E_{l} can be well described by a Lorentzian of energy width Γ_{l} (Hölzer et al., 1997; Deutsch et al., 2004),As dE/E = dλ/λ = ds/s, the function can also be represented as a function of s:For a laboratory tube emitting simultaneously a set of N_{λ} wavelengths, we havewhere w_{l} is the relative intensity of the lth wavelength component (referred, for example, to w_{1} = 1). The corresponding Fourier transform entering (3.6.13) can be written asThe complex term in (3.6.17) accounts for the shift of each emission component with respect to the reference one. For more flexibility (for example to consider the non-ideal behaviour of the instrument), we can use a pseudo-Voigt (pV) in place of the Lorentzian in equation (3.6.14).
References
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