Attenuation coefficients

In this report results of CCF calculations for two mentioned forms of pulses are presented. In these calculations the attenuating coefficient S is replaced by (I-factor of 0)... 

A common contrast agent is barium sulfate [7727-43-7] although iodinated compounds have been used. Owing to the much higher linear attenuation coefficient of the contrast agent, a higher (120 keV) energy x-ray typically is used. 

The transducers on most ultrasound imaging systems operate at a frequency between 1 and 20 MH2. The attenuation, of ultrasound by tissues is both frequency and tissue dependent. The attenuation coefficient, a, of a tissue is defined by equation 5 ... 

G. W. Grodstein, N-Rjoy Attenuation Coefficients from 10 keV to lOOMeV, Cite. 583, U.S. National Bureau of Standards, Washington, D.C., 1957. 

The evaluation of the various XRF measurements will be discussed for different effects in EDXRS the spectra evaluation is perfonned by different programs with varying assumptions, partially different mass attenuation coefficients are used, the calibration procedures are principally different (e.g., thin foils with given thickness, or, infinitely thick samples), measurement under atmospheric pressure or in vacuum, secondary excitation (enhancement) mainly of Al by Si radiation. 

In X-ray spectrometry, attenuation, deflection and interference must be considered. Attenuation is described by the well-known Lambert-Beer law and the mass attenuation coefficient as given for conventional XRF. 

Etherington, 1958 gives the total attenuation coefficient in air p, = 0.0804 cmVgm, and the energy absorption coefficient = 0.0311 cmVgm for tissue. 

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. 

In Temkin s analysis, mass transfer is assumed to be absent in the two-component system. He found that an attenuation coefficient, A, is function of the relaxation times td and t, and the mass fration of suspension, x . 

The rate of photolytic transformations in aquatic systems also depends on the intensity and spectral distribution of light in the medium (24). Light intensity decreases exponentially with depth. This fact, known as the Beer-Lambert law, can be stated mathematically as d(Eo)/dZ = -K(Eo), where Eo = photon scalar irradiance (photons/cm2/sec), Z = depth (m), and K = diffuse attenuation coefficient for irradiance (/m). The product of light intensity, chemical absorptivity, and reaction quantum yield, when integrated across the solar spectrum, yields a pseudo-first-order photochemical transformation rate constant. 

Yasui et al. [29] have used solution of wave equation based on finite element method for characterization of the acoustic field distribution. A unique feature of the work is that it also considers contribution of the vibrations occurring due to the reactor wall and have evaluated the effect of different types of the reactor walls or in other words the effect of material of construction of the sonochemical reactor. The work has also contributed to the understanding of the dependence of the attenuation coefficient due to the liquid medium on the contribution of the vibrations from the wall. It has been shown that as the attenuation coefficient increases, the influence of the acoustic emission from the vibrating wall becomes smaller and for very low values of the attenuation coefficient, the acoustic field in the reactor is very complex due to the strong acoustic emission from the wall. 

The value of p, the linear attenuation coefficient, depends on the substance, its density, and on the wavelength of the x-rays [2]. The mass attenuation coefficient, p., is obtained by dividing p, by the density of the substance. Although a powder mixture may be composed of several components, it can be regarded as being composed of just two components component J (which is the unknown), and the sum of the other components (which is designated as the matrix). The intensity of line i of component J in a powder mixture is given as... 

It is possible to calculate the mass attenuation coefficient value of a compound from its elemental composition. If wh w2,. . wn are the weight fractions of elements 1, 2,. . ., n in the compound and x 1, p.2, .. ., x are their respective mass attenuation coefficients (for radiation of a particular wavelength), then the mass attenuation coefficient of the compound, x, is [2]... 

The mass attenuation coefficient values of the elements are available in the literature [46]. Therefore, the mass attenuation coefficient of a compound can be calculated. Thus and (in Eq. 15) can be calculated provided the molecular formulas of components 1 and 2 are known. It is then possible to calculate the intensity ratio, /u/(/ii)o> as a function of xx. This ratio can also be experimentally obtained. The intensity of peak i of a sample consisting of only 1 is determined [(/ii )o] This is followed by the determination of the intensity of the same peak in mixtures containing different weight fractions of 1 and 2. This enables the experimental intensity ratio, /n/(/n)o, to be obtained as a function of xx. The principles discussed above formed the basis for the successful analyses of quartz-beryllium oxide and quartz-potassium chloride binary mixtures [45]. 

In this series, fi and /x are respectively the mass attenuation coefficients of anhydrous carbamazepine and carbamazepine dihydrate. The calculated values were fi = 5.21 cm2 g-1 and /x = 5.87 cm2 gThe theoretical line in Fig. 5 is based on these values. 

Ablation products attenuation coefficient (10 cm ) Ablation rate constant (ng.ns. MW. cm )... 

Relatively few data exist on the attenuation of various bodily tissues due to scattering and absorbance the data in Figure 6.18 are a compilation.(73) Attenuation is expressed as an effective attenuation coefficient expressed in crrT1, which is the sum of contributions of attenuation due to scattering and absorbance ... 

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