Monochromator primary

A highly monochromated primary electron beam (energy 1—50 eV) impinges on a sample. Many electrons are elastically scattered directly from the surface whereas others undergo inelastic scattering by exciting a vibrational state of atoms in the surface layers. The scattered electrons reflected back from the surface are collected and their energies are analysed. 

Dyes with OjO -hydroxycarboxyazo and OjO -hydroxyaminoazo ligands are important for yeUow shades. Anthranilic acid [118-92-3] is used advantageously with various couplers. OjO -Hydroxyaminoazo dyes are also used to obtain green and brown shades. An example is Monochrome Brown EB [3564-15-6] (54) (Cl Mordant Brown 1 Cl 20110) an unsymmetrical primary disazo dye. 

HREELS experiments [66] were performed in a UHV chamber. The chamber was pre-evacuated by polyphenylether-oil diffusion pump the base pressure reached 2 x 10 Torr. The HREELS spectrometer consisted of a double-pass electrostatic cylindrical-deflector-type monochromator and the same type of analyzer. The energy resolution of the spectrometer is 4-6 meV (32-48 cm ). A sample was transferred from the ICP growth chamber to the HREELS chamber in the atmosphere. It was clipped by a small tantalum plate, which was suspended by tantalum wires. The sample was radia-tively heated in vacuum by a tungsten filament placed at the rear. The sample temperature was measured by an infrared (A = 2.0 yum) optical pyrometer. All HREELS measurements were taken at room temperature. The electron incident and detection angles were each 72° to the surface normal. The primary electron energy was 15 eV. 

As area detectors (other than multiwire systems) are not energy discriminating devices, apotential source of error lies in the contamination of the data with harmonics of the assumed wavelength of the primary beam. The importance of this effect has been estimated for molybdenum Ka radiation using a graphite monochromator [1],... 

There are four approaches to remove or account for this effect (i) primary radiation free of any )12 component can be produced (ii) a Si or Ge monochromator may be used (iii) the 12 component of the scattered radiation can be determined (iv) an independent determination of the amount of 12 scattering may be carried out. 

The amplitude of I m for Si or Ge is close to zero, therefore the contribution of 12 to the 111 reflection is zero. Hence, the 111 reflection from a Si or Ge monochromator is used to obtain 12 free radiation. However, these monochromators also drastically reduce the intensity of the primary beam compared to the graphite monochromators found in most commercial diffractometers. 

Optical devices are placed in the light path in order to shape the primary beam. Beam-position monitors, shutters, slits, monochromators, stabilizers, absorbers, and mirrors are utilized for this purpose. The effective beam shape and its flux are defined by these components. In particular, if mirrors are cooled, vibration must be avoided and thermal expansion should be compensated. 

Laboratory X-ray sources emit highly divergent radiation. With conventional optics the major part of this radiation is discarded by a slit system and a monochromator. Both components can be replaced by a Gobel mirror [73,74], Figure 4.5 shows its construction and application. As a result a parallel and highly monochromatic primary beam is received. Replacement of conventional incident beam optics (cf. Fig. 2.2) by a Gobel mirror increases the primary beam intensity by a factor of 10-50. 

This is most easily done at a laboratory source where the current of the X-ray tube is decreased to the lowest possible value. At a synchrotron beamline this is more complicated, because the measurement of the primary beam requires special adjustment. So, technically this should be done before the final optical adjustment of the device, as long as the slits can be narrowed for the purpose of intensity attenuation and as long as the primary beam stop is not yet mounted. It is not advised to use absorbers that are mounted behind the monochromator, because they change the spectral composition of the X-ray beam. 

The instrumentation required for atomic fluorescence measurements is simpler than that used for absorption. As the detector is placed so as to avoid receiving radiation directly from the lamp, it is not strictly necessary to use a sharp-line source or a monochromator. Furthermore, fluorescence intensities are directly related to the intensity of the primary radiation so that detection limits can be improved by employing a high-intensity discharge lamp. 

Fig. 1. Typical locations for CAM components, showing the photometer, 1 filter wheel, 2 monochromator, 3 shutter and aperture unit, 4 beam splitter, 5 accessories for polarized light such as a rotary analyzer and a compensator, 6 beam splitter for epi-excitation fluorescence, 7 objective lens, 8 stage, 9 substage condenser, 10 condenser aperture, 11 polarizer, 12 field aperture for photometry, 13 shutter, 14 primary illuminator, 15 arc lamp, 16 shutter, 17 monochromator, 18 filter wheel, 19 and ocular, 20.

Spectral interferences are due to substances in the flame that absorb the same wavelength as the analyte, causing the absorbance measurement to be high. The interfering substance is rarely an element, however, because it is rare for another element to have a spectral line at exactly the same wavelength, or near the same wavelength, as the primary line of the analyte. However, if such an interference is suspected, the analyst can tune the monochromator to a secondary line of the analyte to solve the problem. 

Despite the measurement of the emitted radiation by these means it is still possible for scattered or reflected incident radiation to reach the detector. To prevent this, fluorimeters require a second monochromating system between the sample and the detector. Many simple fluorimeters use filters as both primary and secondary monochromators but those instruments that use true optical monochromators for both components are known as spectrofluo-rimeters. Other instruments incorporate a simple cut-off filter system for the emitted radiation while retaining the optical monochromator for the excitation radiation. Because the wavelengths of both excitation and emission are characteristic of the molecule, it is debatable which monochromator is the most important in the design of a fluorimeter. 

Figure 5.25 — Flow-through ion-selective optrode based on a multilayer lipidic membrane prepared by the Langmuir-Blodgett method. (A) Cross-sectional view of the composite six-layer membrane (four layers of arachidic acid/ valinomycin covered by an arachidic acid and rhodamine dye bilayer). (B) Optical arrangement integrated with the sensor, which is connected to a flow system. LS light source Ml and M2 excitation and emission monochromator, respectively FI and F2 primary filters M mirror LB lipid-sensitive membrane in a glass platelet FC flow-cell A amplifier D display P peristaltic pump. (Reproduced from [107] with permission of the Royal Society of Chemistry).

An EXAFS experimental set-up has three primary components (i) a source of X-rays, (ii) a monochromator (and collimator) and (iii) a detector. Synchrotron radiation is being widely used for EXAFS, but where this facility is not available, a rotating anode source would be suitable. Progress in EXAFS instrumentation has been comprehensively reviewed in the AIP proceedings (1980). 

Double immunofluorescence labeling in conjunction with microwave heating can be used to visualize two markers at the same cellular location in routine formalin-fixed and paraffin-embedded tissue sections (Mason et al 2000). The primary antibodies are either monoclonal antibodies of differing isotype/subclass or antibodies from different species. Labeling is visualized on a conventional fluorescence microscope equipped with a cooled analog monochrome CCD camera (Model C 5985, Hamamatsu Photonics, Billerica, MA) and recorded using off the shelf personal computer hardware and software. Contrary to general belief, paraffin-embedded tissue sections do not show excessive nonspecific fluorescence. 

Comparison of Fig. 1, which depicts a conventional CD system, and Fig. 4 shows the primary difference in the two approaches to be in the type and location of the wavelength dispersion device. For multichannel detection, the monochromator has been replaced by a polychromator which does not possess an exit slit to define a wavelength interval. For multichannel detection, the location (pixel) on the multichannel device defines the wavelength of interest. In conventional approaches, the monochromator is placed after the source in order to limit the UV exposure of the sample. However, in the multichannel arrangement, the polychromator is located after the sample to allow the sample to be... 

Again, in HR-CS AAS these problems are essentially nonexistent for the same reasons as given above. Firstly, because of the relatively constant, very intense emission of the primary radiation source, there are no more weak lines that is, the same high SNR will be obtained on all analytical lines, regardless of their spectral origin. The only factors that will have an influence will be the absorption coefficient and the population of the low excitation level in case nonresonance lines are used. Secondly, because of the high resolution of the monochromator, and the visibility of the entire spectral environment of the analytical line in HR-CS AAS, potential spectral interferences can easily be detected, and in addition cannot influence the actual measurement, except in the rare case of direct line overlap. However, even in this case, HR-CS AAS provides an appropriate solution, as discussed in the previous section. 

The primary advantages of vector CRTs are the ability to produce sharp clean images. The drawbacks are the limited colors available (monochrome usually, expensive beam penetration units can produce several) and the fact that the user has to choose between a static display for a large number of lines or contend with flicker on a display which can be updated. 

Briefly, the total linear absorption coefficient n (cm-1) varies as a function of the wavelength and the nature of the absorber as the photon energy is varied across and beyond the absorption edge. The logical setup for an absorption experiment in transmission mode therefore consists of three primary components (Fig. 2a) (i) an X-ray source, (ii) a monochromator (and collimator), and (iii) a detector. In this case Beer s law,... 

The primary use of lithium fluoride is in the ceramic industry. It reduces the firing temperature and improves the resistance to abrasion, acid attack and thermal shocks. It is essential component of the fluorine cell electrolyte. An addition of small amount (1-1.5%) to KHF2 HF electrolyte improves the wettability of the carbon anodes and lowers the tendency of the cell to polarize. Another important use of LiF is in flux compositions containing chlorides, borates and other fluorides. Lithium fluoride windows made from high purity crystals are used for X-ray monochromators, UV, visible or IR regions [18]. 

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