Attenuation and absorption

Fig. 4. The attenuation and absorption of the ETR spectral distribution by the atmosphere. Top curve is the ETR spectral distribution. In decreasing order, the global, direct, and diffuse spectral distributions at the bottom of the atmosphere (at sea level) for the sun at zenith angle...

Variations in DOC quality (DOC - specific attenuation and absorption) warrant further discussion. These variations can be divided into two related categories changes in specific attenuation correlated with DOC concentrations, and changes in specific attenuation correlated with lake and watershed characteristics. The immediate basis for the power relationships between K io [DOC] (Table 3) comes directly from the power relationship between ad32o and [DOC] (Table 2) for the data of Morris et al. [60]. But why should DOC quality change together with DOC concentration over the scale of lakes in this study What determines the exponent in the power model relating specific absorption and DOC concentration ... 

Each of these is characterized by a mass attenuation coefficient which are, respectively, r/p, o/p and zc/p. To each there is a corresponding total energy absorption coefficient. The mass attenuation and absorption coefficients for aluminium and water are given in Fig. 1. 

Gamma-Ray Attenuation and Absorption. The attenuation of gamma radiation follows an approximately exponential law,... 

This is the parameter plotted in Figure 2.2, comparing attenuation and absorption. The attenuation coefficient only expresses the probability that a gamma-ray of a particular energy will interact with the material in question. It takes no account of the fact that as a result of the interaction a photon at a different energy may emerge as a consequence of that interaction. The total absorption coefficient, niust, of course, take into account those incomplete interactions ... 

A good compilation of mass attenuation and absorption coefficients is ... 

An excellent Internet source of attenuation and absorption data is http //physics.nist.gov/PhysRefData/XrayMassCoef/cover. ihtml (Table 3 is particularly useful). 

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. 

Extinction the attenuation of light due to scattering and absorption as it passes through a medium. 

It has always been difficult to do quantitative work with the characteristic x-ray lines of elements below titanium in atomic number. These spectra are not easy to obtain at high intensity (8.4), and the long wavelength of the lines makes attenuation by absorption a serious problem (Table 2-1). The use of helium in the optical path has been very helpful. The design of special proportional counters, called gas-flow proportional counters,20 has made further progress possible, and it is now possible to use aluminum Ka (wavelength near 8 A) as an analytical line (8.10). 

Fig. 3-3. Attenuation and filtering of polychromatic x-rays by aluminum. Variation of effective wavelength with thickness. The effective wavelengths shown in tin figure correspond to the measured mass absorption coefficients. The change ir effective wavelength accounts for the deviations from the (dashed) straight lines The x-ray intensities used gave 210 /xamp through 0.0127-cm aluminum (curve A) 3200 /xamp through 0.381-cm aluminum (curve B). (Liebhafsky, Smith, Tanis, anc Winslow, Anal. Chem., 19, 861.)...

We are interested in the transmission of y-quanta through the absorber as a function of the Doppler velocity. The radiation is attenuated by resonant absorption, in as much as emission and absorption lines are overlapping, but also by mass absorption due to photo effect and Compton scattering. Therefore, the number Tt E2)AE of recoilless y-quanta with energies EXo E + AE traversing the absorber is given by... 

Fig. 2.3.4 Film formation of a photoinitiated the lower surface (left) after a 90 min induction cross-linking latex coating as measured by period due to oxygen absorption. The profiles CARField. (a) The coating is exposed to air shown were recorded 10, 90, 100 and 110 min (evaporation) and light from above, (b) A sam- and 2, 3, 4, 5, 6 and 17 h after casting the layer, pie comprising a combination of only polymer (d)The full formulation film forms in the central and water dries from the upper surface (right) layers first. In this final time series, the profiles as shown by a time series of profiles, recorded shown were recorded after 10 min (dotted at 10, 20, 30, 40, 50, 60, 70, 100 and 120 min trace, T) attenuated) and then, from the top after casting the layer, (c) A combination of down, 30, 60 and 90 min and 2, 3, 6 and 17 h polymer and photoinitiator only cures from after casting the layer.

The attenuation of an optical fibre results from physical phenomena either occurring within the fibre or coming from the environment. This is the sum of light lost by scattering in the fibre, absorption by the fibre materials, leakage of light out of the core due to environmental factors (e.g. microbends). Scattering and absorption losses dominate in every fibre. 

The matrix however may bring about considerable attenuation, and for a multi-element target the mass absorption coefficients are additive. 

In multicomponent systems A"0 can be written as a sum of the individual absorption coefficients A ot = 2TA , where each AT,(A ) depends in a different way on the wavelength. If one or more of the components are fluorescent, their excitation spectra are mutually attenuated by absorption filters of the other compounds. This effect is included in Eqs. (8.27) and (8.28) so that examples like that of Figure 8.4 can be quantified. The two fluorescent components are monomeric an aggregated pyrene, Mi and Mn. The fluorescence spectra of these species are clearly different from each other but the absorption spectra overlap strongly. Thus the excitation spectrum of the minority component M is totally distorted by the Mi filter (absorption maxima of Mi appear as a minima in the excitation spectrum ofM see Figure 8.4, top). In transparent samples this effect can be reduced by dilution. However, this method is not very efficient in scattering media as can be seen by solving Eqs. (8.27 and 8.28) for bSd — 0. Only the limit d 0 will produce the desired relation where fluorescence intensity and absorption coefficient of the fluorophore are linearly proportional to each other in a multicomponent system. 

The attenuation coefficient, t, represents a combination of light scattering and absorption by gases and... 

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