Transmission and scattering

We have now surveyed the iron-bearing pigments and, to a limited extent, terra cotta statuary using both transmission and scattering geometry. The results provide information of an extraordinary richness and... 

Positron transmission and scattering measurements using superposition of annihilation line shapes backscatter coefficients. Phys. Rev. A 7 135-145. 

The optical properties of the wall also contribute to the emitted spectra. The usual arc tube wall material, polycrystalline alumina (PCA), has rather low "in-line" transmission and scatters most of the incident radiation. That portion which is scattered back into the discharge medium and that is also in the spectral region inside or near the peaks of the self-reversed resonance lines, is likely to be absorbed. Thus we have found greater Na reversal for PCA arc tube lamps than for sapphire lamps with the same diameters, Na-Hg alloy composition and reservoir temperatures. Indeed, various authors have reported 3-8% higher efficacies for sapphire vs PCA lamps depending upon the quality of the PCA and its surface treatment 3). 

Complex Index of Refraction of Soot. Soot refractive index has been measured by several researchers. The experimental techniques used can be broadly categorized as in situ and ex situ techniques. In the former, the measurements are performed nonintrusively in a flame environment. The necessary information is retrieved either from spectral transmission data or both the transmission and scattering information, as in Refs. 215-224. The ex situ measurements involve the reflection/transmission of incident spectral radiation on planar pellets of soot, and the optical properties are determined using the Fresnel relations [225]. An alternative ex situ technique was used by Janzen [226], who dispersed the soot particles in a KBr matrix and used transmission measurements to extract the required optical properties. 

Corrosion of Metals. Corrosion phenomena of iron, cobalt, tin, and their alloys have been investigated by a variety of Mossbauer techniques by the transmission and scattering methods and by the emission technique in which the specimen under study is doped with a Mossbauer source isotope (e.g., Co) and measured against a single-line resonant... 

Neutron moisture gauges Neutron transmission and scatter methods can be used to measure total hydrogen content, and assumes a constant hydrocarbon hydrogen. 

The Mossbauer (transmission and scattering) spectroscopy has been used for in-situ characterization of the micro structural properties of materials. For thick samples, the MS is done in reflection geometry. As shown in Table 4.1, the range with X-rays is ss 20 pm, but with conversion electrons (GEMS)... 

Gerald Birth (1971) has added to the knowledge of reflectance measurements through extensive work. He reduced the Kubelka Munk theory to several simple equations relating the absorption and scattering coefficients of a sample system to its diffuse reflectance, transmission, and scatter/path-length terms. The reduction of the Kubelka Munk theory is as follows If S = 2s (the scattering coefficient), and K = 2fe (the absorption coefficient), and we express... 

For optical transmission, tire parameters of greatest importance are attenuation (i.e. loss) and material dispersion. In effect tliey define tire limits of tire optical communication system. Loss, due to absorjDtion and scattering, limits tire lengtlis between tire transmission nodes. In transmission quality fibre, tire loss is in units of decibels per kilometre. 

Attenuation. The exceptional transparency, or low attenuation, of siUca-based glass fibers has made them the predominant choice for optical transmission because of the low level of absorption and scattering of light as it traverses the material. Together these comprise optical attenuation, or loss, measured in dB where... 

The atmospheric transmissivity, t, greatly affects the radiation transmission by absorption and scattering by the separating atmosphere. Absorption may be as high as 20-40%. Pietersen and Huerta (1985) give a correlation that accounts for humidity (equation 9.1-31), where t = atmospheric transmissivity, = water partial pressure (Pascals), X = distance from flame surface to target (m). 

Transmissivity The fraction of radiant energy transmitted from a radiating object through the atmosphere to a target after reduction by atmospheric absorption and scattering. 

The most ubiquitous method of transmission spectroscopy, in which the amount of light passing through a sample is determined. Very often the influence of reflection and scattering is neglected and the ratio of incident and transmitted intensity ( / ) is linked to the absorption coefficient (a) and the sample thickness (d) by Lambert-Beer s law (see Eq. (9.11)). 

A further benefit of the low absorbtivity of most samples in the NIR is that measurements involving scattering effects (both diffuse transmission and diffuse reflectance) are possible. The penetration depth of the sampling beam in diffuse reflectance measurements of powders in the NIR can be on the scale of millimeters, despite the numerous refractive index interfaces and extended optical path involved. Thus relatively large volumes of material can be interrogated, avoiding problems of surface contamination and sample nonhomogeneity. 

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