Diffraction of radiation

In order to explain the diffraction of radiation on the quantum theory, the writer proposed1 an hypothesis according to which the momenta of the radiation quanta are transferred to the diffracting material in multiples of Ifija where h is Planck s action constant and a is a grating space." The momenta of a quantum transferred in the directions of three axes may be written... 

The particular sensitivity of diffuse-reflection spectroscopy to surface structures, is due to the usually multiple reflection and diffraction of radiation at the surfaces of the scattering particles. Therefore catalytic processes and chemically modified surfaces are frequently studied this way. 

Adsorption of radiation Scattering of radiation Refraction of radiation Diffraction of radiation Rotation of radiation Electrical potential Electrical current Electrical resistance Mass to charge ratio Rate of reaction Thermal properties Mass Volume... 

The physics of diffraction by crystals has been worked out in detail. It is found that the incident radiation is scattered in a characteristic way, called a diffraction pattern. The positions and intensities of the diffracted beams are a function of the arrangements of the atoms in space and some other atomic properties, such as the atomic number of the atoms. Thus, if the positions and the intensities of the diffracted beams are recorded, it is possible to deduce the arrangement of the atoms in the crystal and their chemical nature. The determination of crystal structures by use of the diffraction of radiation is outlined in Chapter 6. 

Figure 8.38 Diffraction of radiation of different wavelengths. Overlap can occur when different orders are diffracted at the same angle.

Figure 2.9 Diffraction of Radiation from a 3-D and 2-D Lattice Arrangement...

Diffraction of radiation takes place when the distance between the scattering centers is comparable to the wavelength of the radiation. 

We need to point out that, if the wavelengths of laser radiation are less than the size of typical structures on the optical element, the Fresnel model gives a satisfactory approximation for the diffraction of the wave on a flat optical element If we have to work with super-high resolution e-beam generators when the size of a typical structure on the element is less than the wavelengths, in principle, we need to use the Maxwell equations. Now, the calculation of direct problems of diffraction, using the Maxwell equations, are used only in cases when the element has special symmetry (for example circular symmetry). As a rule, the purpose of this calculation in this case is to define the boundary of the Fresnel model approximation. In common cases, the calculation of the diffraction using the Maxwell equation is an extremely complicated problem, even if we use a super computer. 

Diffraction is the deflection of beams of radiation due to interference of waves that interact with objects whose size is of the same order of magnitude as the wavelengths. Molecules and solids typically have... 

Flendrickson W A 1991 Determination of macromolecular structures from anomalous diffraction of synchrotron radiation Soienoe 254 51-8... 

The construction of a typical monochromator is shown in Figure 10.12. Radiation from the source enters the monochromator through an entrance slit. The radiation is collected by a collimating mirror, which reflects a parallel beam of radiation to a diffraction grating. The diffraction grating is an optically reflecting surface with... 

As in all Fourier transform methods in spectroscopy, the FTIR spectrometer benefits greatly from the multiplex, or Fellgett, advantage of detecting a broad band of radiation (a wide wavenumber range) all the time. By comparison, a spectrometer that disperses the radiation with a prism or diffraction grating detects, at any instant, only that narrow band of radiation that the orientation of the prism or grating allows to fall on the detector, as in the type of infrared spectrometer described in Section 3.6. 

Diffraction of electromagnetic radiation by atoms and molecules occurs when the wavelength of the electromagnetic radiation is similar to the size of the particle that causes the diffraction—in this case, atoms or molecules, (a) Using 2.0 X 102 pm as the diameter of an atom, decide what type(s) of... 

In an x-ray diffraction experiment on a single crystal of sodium chloride, with the use of radiation from a copper source (X = 154 pm), constructive interference was observed at 0 = 11.2°. What is the spacing of the layers responsible for the diffraction ... 

The basic instrumentation used for spectrometric measurements has already been described in the previous chapter (p. 277). Methods of excitation, monochromators and detectors used in atomic emission and absorption techniques are included in Table 8.1. Sources of radiation physically separated from the sample are required for atomic absorption, atomic fluorescence and X-ray fluorescence spectrometry (cf. molecular absorption spectrometry), whereas in flame photometry, arc/spark and plasma emission techniques, the sample is excited directly by thermal means. Diffraction gratings or prism monochromators are used for dispersion in all the techniques including X-ray fluorescence where a single crystal of appropriate lattice dimensions acts as a grating. Atomic fluorescence spectra are sufficiently simple to allow the use of an interference filter in many instances. Photomultiplier detectors are used in every technique except X-ray fluorescence where proportional counting or scintillation devices are employed. Photographic recording of a complete spectrum facilitates qualitative analysis by optical emission spectrometry, but is now rarely used. 

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