Radiation, electromagnetic reflections

Attenuation of radiation as it passes through the sample leads to a transmittance of less than 1. As described, equation 10.1 does not distinguish between the different ways in which the attenuation of radiation occurs. Besides absorption by the analyte, several additional phenomena contribute to the net attenuation of radiation, including reflection and absorption by the sample container, absorption by components of the sample matrix other than the analyte, and the scattering of radiation. To compensate for this loss of the electromagnetic radiation s power, we use a method blank (Figure 10.20b). The radiation s power exiting from the method blank is taken to be Pq. 

The science known as spectroscopy is a branch of physics that deals with the study of the radiation absorbed, reflected, emitted, or scattered by a substance. Although, strictly speaking, the term radiation only deals with photons (electromagnetic radiation), spectroscopy also involves the interactions of other types of particles, such as neutrons, electrons, and protons, which are used to investigate matter. 

Measurement of the quantity and quality of electromagnetic radiation emitted, reflected, transmitted, or diffracted by the sample. 

Fig. 12.2 Conversion of linearly polarized electromagnetic radiation into ellipti-cally polarized radiation by reflection. Consideration of the electric vector, (a) Decomposition of E in components perpendicular and parallel to the plane of incidence (b) Example after reflection the vector moves anticlockwise (c) Representation in three dimensions.

If it is no longer possible to differentiate between the phenomena of specular reflection, refraction and diffraction because the diameter d of the sample to be assayed is disproportionately greater than the wavelength X of the light (i.e. the electromagnetic radiation), the reflection must be considered to be diffuse. 

Microwave sensors are based on radiation and reception of electromagnetic radiation In the GHz range. Because of the Doppler effect, the frequency of the reflected wave will differ from that of the emitted wave In relation to the speed of the object reflecting the radiation. The reflected wave Is compared with the Initial emitted wave. 

In the second broad class of spectroscopy, the electromagnetic radiation undergoes a change in amplitude, phase angle, polarization, or direction of propagation as a result of its refraction, reflection, scattering, diffraction, or dispersion by the sample. Several representative spectroscopic techniques are listed in Table 10.2. 

Radiation. All materials radiate thermal energy in the form of electromagnetic waves. When this radiation falls on a second body it may be partially reflected, transmitted, or absorbed. It is only the fraction that is absorbed that appears as heat in the body. 

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