Diffracted Beam Part consists of Diffracted Beam Optics and Detectors.

To see detailed overview, please click on items listed on the left.

 

Diffracted Beam Slits

Slits used on the diffracted beam path can be divided into:

Receiving slits

They are placed in the diffraction beam path on the diffractometer circle. For parafocusing applications this position forms the focusing point of the diffracted x-ray beam.

Receiving slits for high resolution x-ray diffraction

In HR rocking curve measurements the resolution is determined by the incident beam monochromator and the sample. In these applications the receiving slit is used to reduce the background radiation or to reduce the acceptance of the detector in the 2q direction.

Note:
Receiving Slits listed above can also be used for HR diffraction.

Triple Axis & Rocking Curve Attachment

This PreFIX module combines a triple axis and rocking curve attachments designed for rocking curve (RC) measurements and reciprocal space mapping (RSM). It provides two different diffracted beam path options.

One path is Rocking Curve Attachment. There is a slit holder for mounting slits in front of the detector to reduce the beam acceptance angle. The slit holder has a 6 mm aperture.

Second path carries an analyzer crystal to convert the diffractometer to Triple Axis mode. The analyzer crystal is a channel cut Ge crystal. The diffracted beam undergoes two (220) reflections within the groove before entering the detector. The acceptance angle of the analyzer crystal is 12 arc sec.

The TA/RC attachment uses two detectors: one (Detector 1) is situated at TA path, another (Detector 2) is shared between RC path and Parallel Beam Collimator attachment.

Parallel Plate Collimator Attachment

This attachment combines parallel plate collimator and flat graphite monochromator in one PreFIX module.

Diffracted beam collimator is an optical module used in the quasi-parallel beam geometry to define acceptance angle of the diffracted beam seen by the detector. The parallel plate collimator (PPC) consists of a set of parallel plates perpendicular to the diffraction plane. The distance between the plates defines the acceptance angle of the collimator. The collimator in the X-ray Lab has equatorial acceptance of 0.27o.

A collimator slit with an equatorial aperture of 0.1 mm can be mounted together with the PPC. This slit is mainly used for reflectivity measurements to enhance the resolution at very low 2q angles (< 4o).

Another part of the PPC Attachment is diffracted beam flat crystal monochromator. It is used to reduce the background radiation, eliminate Kb line and reduce the effect of sample fluorescence. The crystal used in the monochromator is a flat pyrolytic graphite crystal. The reflectivity for Cu Ka radiation is between 25% and 40%. The rocking width of the crystal is 0.4o.

A detector slit with a chemical symbol "Cu" can be used with a flat crystal monochromator. It is used to prevent the x-ray beam coming off the parallel plate collimator being accepted by the detector without having been diffracted by the monochromator.

 

 

 

Detectors

X-ray detector is used to count the number of photons (intensity) of the diffracted beam at certain 2q position of the goniometer. X'Pert diffractometer uses sealed proportional detectors - sealed chambers filled with xenon/methane gas mixture.

 

General properties of the Proportional Detector

Window size	20 X 24 mm2
Efficiency Cu Ka	84%
Efficiency Mo Ka	36%
99% Linearity range	0 - 500,000 cps
Energy resolution around Cu Ka	19%
Maximum count rate	750,000 cps
Maximum background	2 cps

- The linearity range is defined as the range within which the deviation from the linear relationship between the incoming and counted x-ray photons is less than 1%.
- The energy resolution is determined by the ratio of the Full Width at Half Maximum and the peak position of the pulse height distribution.
- The maximum count rate defines the maximum intensity of the x-ray beam to which the detector may be exposed.

Diffracted Beam Slits

Triple Axis & Rocking Curve Attachment

Parallel Plate Collimator Attachment

Detectors