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Several
factors influence the choice of anode and focus.
The
primary considerations include the use of the tube,
whether for powder diffractometry or single work,
together with the minimisation of the background
radiation.
The
selection then depends on factor such as the sample
penetration required, the d-value range under study and
possible problems with fluorescence of the sample.
For
most diffractometry applications, both high resolution
and high intensity are desirable. Here, a long fine focus tube offers great advantages, combining the
resolution of a fine focus tube with much of the
intensity of a broad focus tube.
The
degree of collimation normally employed in camera work
demands a high intensity source, such as is provided by
a fine focus
tube.
Normal
focus
tubes offer a compromise between intensity and line
resolution, for example they can be employed to
advantage when both a point-focus camera and a
diffractometer are to be mounted on a single tube shield.
In
quantitative X-ray diffractometry the degree of
collimation is comparatively minor, while the sample is
usually large. If intensity is the only major
requirement then a broad focus tube is preferred. |
