Instrumental resolution as a function of scattering angle and wavelength as exemplified for the POWGEN instrumentстатья
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Дата последнего поиска статьи во внешних источниках: 26 декабря 2017 г.
Аннотация:The method of angular- and wavelength-dispersive (e.g. two-dimensional)
Rietveld refinement is a new and emerging tool for the analysis of neutron
diffraction data measured at time-of-flight instruments with large area detectors.
Following the approach for one-dimensional refinements (using either scattering
angle or time of flight), the first step at each beam time cycle is the calibration of
the instrument including the determination of instrumental contributions to the
peak shape variation to be expected for diffraction patterns measured by the
users. The aim of this work is to provide the users with calibration files and – for
the later Rietveld refinement of the measured data – with an instrumental
resolution file (IRF). This article will elaborate on the necessary steps to
generate such an IRF for the angular- and wavelength-dispersive case,
exemplified for the POWGEN instrument. A dataset measured on a standard
diamond sample is used to extract the profile function in the two-dimensional
case. It is found that the variation of reflection width with 2 and can be
expressed by the standard equation used for evaluating the instrumental
resolution, which yields a substantially more fundamental approach to the
parameterization of the instrumental contribution to the peak shape.
Geometrical considerations of the POWGEN instrument and sample effects
lead to values for , t and L that yield a very good match to the extracted
FWHM values. In a final step the refinement results are compared with the onedimensional,
i.e. diffraction-focused, case.