Scattering characteristic composite particle

Since the molecular composition of materials is not apparent to the naked eye, more sophisticated, indirect techniques are required to determine the structure of a material at a microscopic level. Spectroscopy, in a manner analogous to human vision, uses a beam of particles to illuminate a sample of the material. A machine eye then sees the scattered or transmitted particles and uses the characteristics of these particles to determine the chemical structure and composition of the sample. The particular type of spectroscopy that a chemist might use depends, in part, on the atomic or molecular characteristics that are assumed to be relevant to the sample. 

Megaelectron volt (MeV) ion beam techniques offer a number of non-destructive analysis methods that allow to measure depth profiles of elemental concentrations in material surfaces. Elements are identified by elastic scattering, by specific nuclear reaction products or by emission of characteristic X-rays. With nuclear microprobes raster images of the material composition at the surface can be obtained. Particle-induced gamma-ray emission (PIGE) is especially suited for fluorine detection down to the ppm concentration level. 

This is the most widely used method for the determination of the phase composition of powders. The x-ray diffractometer contains a source of monochromatic x-rays that irradiate the sample and are diffracted from atomic planes and detected. The angle of diffraction of x-rays by the crystalline planes is characteristic of the crystal structure, and the intensity of scattered radiation is characteristic of the atomic composition. In recent years, automated data processing has enabled higher accuracy and speed. A number of problems are encountered in the quantitative determination of phases in fine powders. Some of these are overlap of phase peaks (e.g., in silicon nitride), orientation of grains, and presence of coarse particles. The last produces distortion of the diffraction data. A number of standard reference materials for XRPD have been developed for use in improving the quality of data [37]. 

The spectral dependence of polarization is also an important observational characteristic of comets that is an indicator of the composition and size of the scattering particles [70]. Prior to comet-Halley observations, two trends were discussed polarization of comets increases with wavelength [4] and polarization of comets is wavelength independent [71,72]. Observations of comets West [4,73], Halley [34,47,74,75], and Hale-Bopp [27,30,76] confirmed that within a = 30° - 80° the polarization of dust-rich comets usually increases with increasing wavelength in the wide spectral range (0.36 - 2.2 pm) (Fig. 6). 

A small-angle X-ray scattering(SAXS) study of a model copolymer latex, based on styrene and pentabromobenzyl acrylate(PBBA, 40 wt %), was conducted. The contrast variation method used was shown to be a sensitive probe for inhomogeneity in the particles. The separation of the homogeneous function allowed direct calculation of the size distribution of the spherical particles. The SAXS analysis revealed a particle s inner structure which was a continuous copolymer phase, the composition of which was slightly richer in PBBA, within which domains of PS were randomly distributed. The volume fraction of the PS domains was estimated as 11 vol % and their characteristic length as 5.1 nm. 24 refs. 

The optical characteristics of diffuse reflectance have been recognized to be dependent on the composition of the system. Several models for diffuse reflectance have been proposed based on the radiative transfer theory, and all these models consider that the incident light is scattered by particles within the medium. The most widely used is the Kubelka-Munk theory, in which it is assumed that the scattering layer is infinitely thick. The reflectance R is related to the absorption coefficient K and the scattering coefficient S by the equation... 

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