Scattering with other radiation

Scattering with other radiation 7.2.2.1 Low angle X-ray scattering 

Low angle X-ray scattering is an experimentally demanding technique and it is certainly not one of standard tools of the biochemical, or even biophysical laboratory. 

Every particle has a wave-like character. Following the de Broglie equation, a particle of mass m moving at a velocity v is associated with a wavelength given by the equation 

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Nuclear excitation and nuclear resonant scattering with synchrotron radiation have opened new fields in Mossbauer spectroscopy and have quite different aspects with the spectroscopy using a radioactive source. For example, as shown in Fig. 1.10, when the high brilliant radiation pulse passed through the resonant material and excite collectively the assemblies of the resonance nuclei in time shorter than the lifetime of the nuclear excited state, the nuclear excitons are formed and their coherent radiation decay occurs within much shorter period compared with an usual spontaneous emission with natural lifetime. This is called as speed-up of the nuclear de-excitation. The other de-excitations of the nuclei through the incoherent channels like electron emission by internal conversion process are suppressed. Synchrotron radiation is linearly polarized and the excitation and the de-excitation of the nuclear levels obey to the selection rule of magnetic dipole (Ml) transition for the Fe resonance. As shown in Fig. 1.10, the coherent de-excitation of nuclear levels creates a quantum beat Q given by... 

Minimizing Spectral Interference A spectral interference occurs when an analyte s absorption line overlaps with an interferant s absorption line or band. As noted previously, the overlap of two atomic absorption lines is seldom a problem. On the other hand, a molecule s broad absorption band or the scattering of source radiation is a potentially serious spectral interference. 

Silver halide fibres (AgClxBri x) have the widest spectral range in the mid-IR, well into the fingerprint range. Due to their crystalline nature, they have a superior flexibility. Problematic is their tendency to decompose upon contact with UV radiation or base metals. Also sulphides will chemically destroy the fibre material. Other points against are the high intrinsic attenuation due to absorption by impurities or scattering at inclusions or micro-crystals and the non-availability of (applicable) core-clad fibres. 

In this chapter we consider the physics of the positronium atom and what is known, both theoretically and experimentally, of its interactions with other atomic and molecular species. The basic properties of positronium have been briefly mentioned in subsection 1.2.2 and will not be repeated here. Similarly, positronium production in the collisions of positrons with gases, and within and at the surface of solids, has been reviewed in section 1.5 and in Chapter 4. Some of the experimental methods, e.g. lifetime spectroscopy and angular correlation studies of the annihilation radiation, which are used to derive information on positronium interactions, have also been described previously. These will be of most relevance to the discussion in sections 7.3-7.5 on annihilation, slowing down and bound states. Techniques for the production of beams of positronium atoms were introduced in section 1.5. We describe here in more detail the method which has allowed measurements of positronium scattering cross sections to be made over a range of kinetic energies, typically from a few eV up to 100-200 eV, and the first such studies are summarized in section 7.6. 

Scattering and other forms of spectroscopy Rely on the fact that electromagnetic radiation has other interactions with matter beyond that of simple absorption and emission. These interactions generate other measurable quantities such as scattering of polarized light (e.g. circular dichroism), and changes of spectral features of chemical bonds (e.g. Raman spectroscopy). 

As in conventional Mossbauer spectroscopy, Fe is the most widely used isotope in nuclear resonant scattering of synchrotron radiation. Experiments with other... 

Absorption or scattering of radioactive radiation is applied in industry for measurement of thickness or for material testing. For example, the production of paper, plastic or metal foils or sheets can be controlled continuously by passing these materials between an encapsulated radionuclide as the radiation source and a detector combined with a ratemeter, as shown in Fig. 20.2. After appropriate calibration, the ratemeter directly indicates the thickness. The radionuclide is chosen in such a way that the radiation emitted is eflFectively absorbed in the materials to be checked. Thus, the thickness of plastic foils is measured by use of f emitters, whereas Cs or other y emitters are used for measuring the thickness of metal sheets. 

These effects, however, are all very weak and are masked by the other forms of diffuse scattering which are always present. As a result, the details shown in Fig. 13-9 are never observed in an ordinary powder pattern made with filtered radiation. To disclose these details and so learn something about the structure of the solid solution, it is necessary to use strictly monochromatic radiation and, preferably, single-crystal specimens, and to make allowances for the other forms of diffuse scattering, chiefly temperature-diffuse and Compton modified, that are always present. 

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