Abstract:
The fundamental parameters approach to
line profile fitting uses physically based
models to generate the line profile shapes.
Fundamental parameters profile fitting
(FPPF) has been used to synthesize and fit
data from both parallel beam and divergent
beam diffractometers. The refined parameters
are determined by the diffractometer
configuration. In a divergent beam diffractometer
these incl ude the angular aperture
of the divergence slit, the width and axial
length of the receiving slit, the angular
apertures of the axial Soller slits, the
length and projected width of the x-ray
source, the absorption coefficient and axial
length of the sample. In a parallel beam
system the principal parameters are the
angular aperture of the equatorial
analyser/Soller slits and the angular apertures
of the axial Soller slits. The presence
of a monochromator in the beam path is
normally accommodated by modifying the
wavelength spectrum and/or by changing
one or more of the axial divergence
parameters. Flat analyzer crystals have
been incorporated into FPPF as a
Lorentzian shaped angular acceptance
function. One of the intrinsic benefits of
the fundamental parameters approach is its
adaptability any laboratory diffractometer.
Good fits can normally be obtained over
the whole 20 range without refinement
using the known properties of the diffractometer,
such as the slit sizes and diffractometer
radius, and emission profile.
