MiniFlex 600: Benchtop X-ray Diffractometer
99
Installing the Counter Monochromator (Optional)
By exploiting the property of a specific filter (Ni for a Cu tube) whereby more Kβ
rays are absorbed than Kα rays, Kβ rays can be attenuated to as low as 1% of Kα
rays. Such a filter is called a Kβ filter. The use of this filter provides Kα ray-only
diffraction patterns. The Kβ filter method, however, may suffer the following
problems:
・
Small peaks deriving from Kβ rays may be detected.
(If an intense diffracted ray is present, a Kβ ray is detected as a small peak at
an angle as low as 10% of that of the Kα ray.)
・
The background may become higher for fluorescent X-rays.
(E.g., when a Fe-containing sample is measured with a Cu tube)
To solve these problems, a counter monochromator (dedicated for Cu tube) is offered as
an option. It is an optical system which disperses a beam by means of a graphite crystal
and only counts the Cu Kα rays, making it possible to cut Kβ rays, continuous X-rays
(white X-rays), and fluorescent X-rays. This accessory provides low background data
free of small diffracted rays deriving from Kβ rays, which are detrimental to qualitative
and other analysis, and enhances the sensitivity to detect small peaks due to impurities
and others causes (see Fig. 11.1, 11.2).
Fig. 11.1 Small diffracted rays deriving from Kβ rays detected with the filter method
(Above: Filter method, Below: Monochromator method)
Fig. 11.2 Difference in the sensitivity to detect small peaks in data between the filter method (above)
and monochromator method (below)
Small peaks form due to K
β
rays only with the filter method.
