Beam attenuation coefficient

Figure 15.11 Decadic beam attenuation coefficients calculated per milligram of DOC as a function of wavelength for a series of water samples from various Swiss lakes and rivers (data from Haag and Hoigne, 1986).

Consider a well-mixed, nonturbid water body with a dissolved organic carbon concentration (DOC) of 4 mg C L-1. The decadic beam attenuation coefficients, a(A), determined for a water sample at five wavelengths are the following (see other examples given in Fig. 15.11) ... 

Decadal beam attenuation coefficients a.(k) of the water at various wavelengths (X) ... 

Figure 14.12 Typical profiles of (A) beam attenuation coefficient (BAG, from Naqvi et al., 1993) and (B) bacterial abundance (10 cells from Ducklow, 1993) within the denitrifying zone. The sampling sites, located close to each other (around 15°N,67°E) had similar N02 distributions (pM) (C, open circles corresponding to microbial data). Subsequent measurements have confirmed the co-occurrence of these features (Naqvi etal., in preparation).

In contrast to AOP s, inherent optical properties (lOP s) depend solely on the water and its optically active constituents. The lOP s include the beam absorption coefficient a , beam scattering coefficient fi , and beam attenuation coefficient c , which are related as follows ... 

Attenuation Coefficient—The fractional reduction in the intensity of a beam of radiation as it passes through an absorbing medium. It may be expressed as reduction per unit distance, per unit mass thickness, or per atom, and is called the linear, mass, or atomic attenuation coefficient, respectively. 

The photoablation behaviour of a number of polymers has been described with the aid of the moving interface model. The kinetics of ablation is characterized by the rate constant k and a laser beam attenuation by the desorbing products is quantified by the screening coefficient 6. The polymer structure strongly influences the ablation parameters and some general trends are inferred. The deposition rates and yields of the ablation products can also be precisely measured with the quartz crystal microbalance. The yields usually depend on fluence, wavelength, polymer structure and background pressure. 

Figure 19 The Z dependence of the ratio of attenuation coefficients of a monoenergetic HI beam to a LO beam of exactly half its energy. The curves strongly depend on the energy of the HI beam, here shown at various values from 40 keV to 10 MeV. With HI energies below 1 MeV, the ratio falls with increasing Z, but above 1 MeV the ratio rises. In either case, the ratio is heuristically seen as a means for determining Z.

From (3.39) and the optical theorem (3.24) it follows that the irradiance is attenuated according to /, = / exp( —aext/j) as the incident beam traverses the slab of particles, where the attenuation coefficient aext is... 

You would like to analyze the atomic structure of Pd by grazing incidence X-ray diffraction. After penetrating a distance x, the intensity of the beam is decreased by I = J0 e x. Your diffractometer uses photons of 10 keV energy. Is the wavelength sufficiently small to analyze atomic structures At this energy a handbook tells you that the photon attenuation coefficient, nip, is 691 cm2/g. The density is 12.0 g/cm3. Assume you want 20% of the incident X-rays to be scattered within the topmost layer of 1 nm thickness. Which angle do you have to choose ... 

Figure 5. The measured attenuation coefficient for die NIST MCP detector at die BT2 thermal neutron beam and the NG1 cold neutron beam.

According to Evans (1995), differentiation of features within the materials is possible because p at each point directly depends on the electron density of the material in that point (pe), the atomic number (Z) of the chemical components of the materials in that point, and the energy of the incoming X-ray beam (/0). In particular, the linear attenuation coefficient can be approximately considered as the sum of the Compton scatter and photoelectric contributions ... 

The attenuation of a light beam is given in terms of the extinction coefficient, sometimes called the attenuation coefficient or turbidity, and it is a key measure of the optical behavior of particulate systems. In terms of the separate contributions for particle scattering and absorption,... 

The attenuation coefficient for a beam of gamma rays is related to the number of gamma rays removed from the beam, either by absorption or scattering. For the Compton effect, the absorption cross section is determined by the energy absorbed by the electron, which is the total collision energy minus the average scattered photon... 

The attenuation coefficients themselves are defined in terms of thickness of material or surface weight of material. This is just using a thickness x (cm) or a surface weight iglcm) where p is the density (in g/cm ). The number of primary photons n removed from a beam of n photons is... 

X-Ray Absorption [1.1,1.8]. The attenuation of X-radiation, which passes through a material of thickness t (cm), is given hy I = Iq exp(—ptX with /q being the intensity of the incident beam, / the intensity of the transmitted beam, and p the linear absorption (attenuation) coefficient. Most tabulations refer to the mass absorption coefficient (p/p), with p being the density of the absorber and having units cm g-... 

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