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A monochromating crystal behaves in X-ray spectrometry as does a diffraction grating in optics. When rotated with respect to the incident beam it will diffract the spectral component in accordance with Bragg’s Law. The most important characteristic of a monochromating crystal is the double atomic spacing 2d, which is the largest wavelength which can be diffracted. The St Gobain Crystals & Detector’s range of synthetic & naturally occurring monochromating crystals offers the widest possible variety of 2d spacing.
Our monochromating crystals are supplied as flat (unmounted or mounted on holders) for XRF spectrometers etc, or curved onto a holder to allow focusing for instruments such as microprobes, scanning electron microscopes etc.
Basic Principle
The spectral analysis of X-Rays emitted by a sample after irradiation is both a powerful qualitative and quantitative analytical technique. It is based on the following phenomenon: an atom relaxes after excitation by emitting characteristic X-Ray radiations, which reveal the identity of the emitting species.
A spectrometer consists of :
- An excitation source generating either X-Rays (for X-Ray fluorescence spectrometers) or electrons ( for microprobes or scanning electron microscopes).
- A monochromating crystal, used to disperse the various spectral components of the incident beam.
The spectral component  1 is diffracted along the  1 direction to satisfy Bragg's law:
2d sin  1 = n  1
where n refers to the diffraction order.
- An X-Ray detector, in order to measure the intensity of the various spectral lines as singled out by the monochromator. St Gobain Crystals & Detectors can offer you the X-Ray detector suitable to your application.
Monochromating Crystals
| Name | Orientation | 2D Spacing
(Angstrom) | Useful Range
(Angstrom) |
| LiF |
200 |
4.027 |
0.351 - 3.840 |
| 220 |
2.848 |
0.248 - 2.720 |
| 420 |
1.801 |
0.157 - 1.720 |
| Quartz |
10 - 10 |
8.514 |
0.742 - 8.340 |
| 10 - 11 |
6.684 |
0.583 - 6.380 |
| InSb |
111 |
7.48 |
0.652 - 7.230 |
| Si |
111 |
6.271 |
0.547 - 5.980 |
| 220 |
3.840 |
0.335 - 3.660 |
| Ge |
111 |
6.532 |
0.570 - 6.230 |
| 220 |
4.000 |
0.349 - 3.820 |
| PET |
002 |
8.740 |
0.762 - 8.340 |
| EDDT |
200 |
8.808 |
0.768 - 8.400 |
| ADP |
101 |
10.648 |
0.654 - 7.160 |
| Beryl |
10 - 10 |
15.950 |
1.390 - 15.220 |
| TIAP |
001 |
25.900 |
2.260 - 24.700 |
| RbAP |
001 |
26.120 |
2.280 - 24.920 |
| KAP |
001 |
26.640 |
2.320 - 25.410 |
Standard products available
Monochromating crystals can be supplied in two shapes depending on the customer application :
Flat plates
- suitable for industrial X-Ray fluorescence spectrometers
- can be supplied unmounted or mounted into holders. The standard orientation accuracy provided is 10 minutes. One minute accuracy can be ensured on special request.
Curved plates
- used in such instruments as microprobes and scanning electron microscopes.
- can be supplied in tailor-made holders.
- two main types of focusing configurations may be considered :
- The Johann geometry
- The Johansson geometry
Other configurations
Other curvatures (logarithmic spiral, spherical, toroïdal..) may be studied on request.
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