The two data sets may be compared directly by plotting in 1/d or d space. Angle-dispersive and energy-dispersive data are usually plotted as a function of 1/d for comparative purposes, but as will be shown later, neutron diffraction data from a pulsed source is usually plotted as a function of d. There are several caveats when converting angle-disperive data to a 1/d scale: it is important to know the wavelength and any angle aberations (e.g. 2θ zero error) precisely; otherwise additional errors can be introduced into the data when converting 2θ values to 1/d (or d) values.
The first data set below shows the laboratory X-ray data set:
The figures below show the same data (X-ray followed by neutron), but now plotted over a smaller range of 1/d so that individual peaks can be seen more clearly. The calculated positions of the peaks is shown in the narrow figure with the magenta vertical tick marks.
As an aside, the X-ray data shown here is better suited for the purpose
of unit-cell indexing than the neutron data, but the latter provides better
structural information on lead sulphate despite the poorer peak resolution
of the diffractometer! Why is this? (You should learn some answers to this
question in this section of the course and in subsequent course material.)
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| © Copyright 1997-2006. Birkbeck College, University of London. | Author(s): Jeremy Karl Cockcroft |