Two Key Components for Spectral Analysis
Monochromating Crystal is used to disperse the various spectral components of the beam emitted by the sample.
Supplying a range of crystals:
LiF, Quartz or SiO2, InSb, Si, Ge, PET, ADP, Beryl, TlAP, RbAP, KAP, and CsAP
Radiation Scintillation Detector used to measure the intensity of spectral lines singled out by the monochromator.
A radiation detector in order to measure the intensity of the various spectral lines as singled out by the monochromator. The detector combining Nal(TI) or LaBr3, coupled to a light-sensing device with a low energy entrance window.
X-Ray Monochromator crystals can be supplied in the two following shapes:
- Flat plates – supplied unmounted or mounted onto holders suitable for industrial X-ray fluorescence spectrometers. The standard orientation accuracy provided is 10 minutes. On special request, a one-minute accuracy can be ensured.
- Curved plates – supplied on tailor-made holders for use in instruments such as microprobes, scanning electron microscopes, Synchrotrons, XFEL, Plasma Physics. Two main types of focusing configurations may be considered: The Johann geometry and The Johansson geometry.
3D curved crystal optics can be provided according to your special finishing requirements: spherical, toroidal, ellipsoidal, conical, others (please inquire)
A thin plate is produced by one of the two following methods:
- Cleavage for LiF (200), PET, TIAP, RbAP, KAP
- Machining for other materials is further cylindrically curved and glued upon a holder of curvature radius 2R.
It is possible to show that a beam emitted by a source at S is approximately focused at F. The source and focus are both located on the so-called Rowland circle whose radius is R
The thin plate is then curved cylindrically and glued to a curved holder with approximate focusing.
Two different types of Johansson configurations, theoretically leading to perfect focusing, are considered:
Single machining Johansson
Double machining Johansson
The illustrations represent the fabrication steps of Johansson plates in both techniques.
The thin plate is either curved cylindrically, glued to a curved holder and one face is machined (single machining Johansson) or both faces are machined and then glued to a curved holder (double machining Johansson).
We will offer the best technique according to the type of crystal, its dimensions and the radius of Rowland circle to be achieved.
Other types of curvature may be investigated on request. For example, curvatures on holders shaped as spiral, elliptic, parabolic, even spheric designs, interesting in plasma or synchrotron radiation study and astrophysics.
Manufacturing capabilities strongly depend upon the crystal nature, dimensions as well as curvature radii.
A monochromating crystal behaves in X-ray spectrometry as does a diffraction grating in optics. When rotated with respect to the incident polychromatic beam (see figure), it will diffract the spectral component along with direction to satisfy Bragg’s law, namely: 2d sin θ = n λ where integer n refers to the diffraction order.
Hence, the most important characteristic of a monochromating crystal is the double atomic spacing 2d, which gives the largest wavelength to be diffracted.
The range of monochromators supplied can be found in Monochromator Crystal Properties along with the usual surface finish, within our control means, to the best intensity-resolution compromise. The optimum depends on each specific case and strongly reflects the nature of the setup.
An X-ray spectrometer basically consists of:
An excitation source may be either a primary X radiation, in which case one refers to X-ray fluorescence spectrometry. Or an electron beam, inducing a so-called direct emission, used in microprobes and scanning electron microscopes.
A monochromating crystal is used to disperse the various spectral components of the incident beam.
A detector in order to measure the intensity of the various spectral lines as singled out by the monochromator.
The detector offered by Saint-Gobain Crystals combines a Nal(TI) or Lanthanum Bromide scintillator directly coupled to a photomultiplier with a low absorbing MIB or beryllium entrance window.
Scroll right for additional crystals →
|Crystal||Lithium fluoride||Quartz||Indium Antimonide||Silicon||Germanium||Pentaerythritol PET||Ammonium Dihydrogen Phosphate ADP||Beryl||Acid Phthalates|
|Thallium TIAP||Rubidium RbAP||Potassium KAP||Cesium CsAP|
|Reflecting planes orientations||(200)||(220)||(420)||(1011)||(1010)||(111)||(111)||(220)||(111)||(220)||(002)||(101)||(1010)||(001)||(001)||(001)||(001)|
|2d in Å||4.027||2.848||1.801||6.684||8.514||7.480||6.271||3.840||6.532||4.000||8.740||10.648||15.950||25.900||26.120||26.640||26.650|
|Usual surface finish||Cleaved or Treated||Treated||Treated||Polished||Polished||Polished||Polished||Cleaved or Treated||Polished or Treated||Polished||Cleaved|
Mo, Fe, Ti
|Mo, Fe||Mo||Cu||Cu||Si||Cu||Cu||Cu||Cu||Al, Si||Mg||Mg||Na, Mg||Na||Na||Na|
|Common Applications||From K to heavy elements||Heavy elements
|As PET||Quantitative analysis of silicon||Extinction of even order spectral lines||Mg||Na and following elements||F to Al||Na to Al, up to F in emission probes||Na to Al, up to F in emission probes||Na to Al, up to F in emission probes|