Détermination du coefficient d'absorption des rayons X à partir des mesures de réflectométrie X

2004 ◽  
Vol 82 (1) ◽  
pp. 75-79 ◽  
Author(s):  
E Ech-chamikh ◽  
I Aboudihab ◽  
M Azizan ◽  
A Essafti ◽  
Y Ijdiyaou
Keyword(s):  
Absorption Coefficient ◽  
Amorphous Carbon ◽  
X Rays ◽  
Absorption Coefficients ◽  
Linear Absorption Coefficient ◽  
Linear Absorption ◽  
Simple Method ◽  
Material Layer ◽  
Reflectivity Spectra ◽  
Good Agreement

In this paper, we present a simple method that allows, among other things, to determine the absorption coefficient of X-rays from reflectivity measurements. This method is applicable if the analysed material is deposited on a substrate denser than the material layer, so that the X-rays reflectivity spectra exhibit two well-resolved descents. In such cases, the amplitude of the first descent (characteristic of the material layer) is directly related to the linear absorption coefficient of the material constituting the layer. We have been able to clarify this relationship and apply it successfully for several cases of materials, especially amorphous carbon and silicon. Values of thus obtained mass absorption coefficients are in very good agreement with those tabulated in the literature.[Journal translation]

scholarly journals The detection of reverse accumulation effect in the positron annihilation profile of stack of aluminum and silver foils

Nukleonika ◽  
2015 ◽  
Vol 60 (4) ◽  
pp. 713-716 ◽  
Author(s):  
Jerzy Dryzek ◽  
Krzysztof Siemek
Keyword(s):  
Absorption Coefficient ◽  
Positron Annihilation ◽  
Linear Absorption Coefficient ◽  
Linear Absorption ◽  
Theoretical Profile ◽  
Accumulation Effect ◽  
The Subject ◽  
Implantation Profile ◽  
Good Agreement

Abstract The implantation profile of positrons emitted from 22Na into a stack of aluminum and silver foils is the subject of the presented report. The characteristic dimple in the profile behind the Ag foil was detected. This effect arises from the differences in the linear absorption coefficient of aluminum and silver. The good agreement between the theoretical profile obtained within the multiscattering model and experimental one was achieved. The observed phenomenon can affect the positron annihilation characteristics measured for the inhomogeneous samples.

scholarly journals Use of radial symmetry for the calculation of cylindrical absorption coefficients and optimal capillary loadings

2015 ◽  
Vol 48 (1) ◽  
pp. 149-158
Author(s):  
Peter Khalifah
Keyword(s):  
Radial Symmetry ◽  
Correction Factors ◽  
Absorption Coefficients ◽  
Linear Absorption Coefficient ◽  
Linear Absorption ◽  
Absorption Correction ◽  
Sample Density ◽  
Diffraction Angle ◽  
Path Lengths ◽  
Cylindrical Samples

The problem of numerically evaluating absorption correction factors for cylindrical samples has been revisited using a treatment that fully takes advantage of the sample symmetry. It is shown that the path lengths for all points within the sample at all possible diffraction angles can be trivially determined once the angle-dependent distance distribution for a single line of points is calculated. This provides advantages both in computational efficiency and in gaining an intuitive understanding of the effects of absorption on the diffraction data. A matrix of absorption coefficients calculated for μRproducts between 0 and 20 for diffraction angles θDof 0–90° were used to examine the influence of (1) capillary diameter and (2) sample density on the overall scattered intensity as a function of diffraction angle, where μ is the linear absorption coefficient for the sample andRis the capillary radius. On the basis of this analysis, the optimal sample loading for a capillary experiment to maximize diffraction at angles of 0–50° is in general expected to be achieved when the maximum radius capillary compatible with the beam is used and when the sample density is adjusted to be 3/(4μR) of its original density.

Measurement of Mass Absorption Coefficients Using Compton-Scattered Cu Radiation in X-ray Diffraction Analysis

1990 ◽  
Vol 34 ◽  
pp. 325-335 ◽  
Author(s):  
Steve J. Chipera ◽  
David L. Bish
Keyword(s):  
Chemical Composition ◽  
Solid State ◽  
Absorption Coefficient ◽  
Mass Absorption Coefficient ◽  
X Rays ◽  
X Ray Diffraction ◽  
Absorption Coefficients ◽  
Solid State Detector ◽  
X Ray ◽  
Mass Absorption

AbstractThe mass absorption coefficient is a useful parameter for quantitative characterization of materials. If the chemical composition of a sample is known, the mass absorption coefficient can be calculated directly. However, the mass absorption coefficient must be determined empirically if the chemical composition is unknown. Traditional methods for determining the mass absorption coefficient involve measuring the transmission of monochromatic X-rays through a sample of known thickness and density. Reynolds (1963,1967), however, proposed a method for determining the mass absorption coefficient by measuring the Compton or inelastic X-ray scattering from a sample using Mo radiation on an X-ray fluorescence spectrometer (XRF). With the recent advances in solid-state detectors/electronics for use with conventional powder diffractometers, it is now possible to readily determine mass absorption coefficients during routine X-ray diffraction (XRD) analyses.Using Cu Kα radiation and Reynolds’ method on a Siemens D-500 diffractometer fitted with a Kevex Si(Li) solid-state detector, we have measured the mass absorption coefficients of a suite of minerals and pure chemical compounds ranging in μ/ρ from graphite to Fe-metal (μ/ρ = 4.6-308 using Cu Kα radiation) to ±4.0% (lσ). The relationship between the known mass absorption coefficient and the inverse count rate is linear with a correlation coefficient of 0.997. Using mass absorption coefficients, phase abundances can be determined during quantitative XRD analysis without requiring the use of an internal standard, even when an amorphous component is present.

scholarly journals Continuous absorption

1930 ◽  
Vol 229 (670-680) ◽  
pp. 163-204 ◽  
Keyword(s):  
Absorption Coefficient ◽  
Bound State ◽  
Free State ◽  
X Rays ◽  
Classical Electromagnetism ◽  
Considerable Difficulty ◽  
Positive Nucleus ◽  
Continuous Absorption ◽  
The Matrix ◽  
Good Agreement

For some years astrophysicists have been looking for an adequate theory of continuous—as opposed to line—absorption. The natural and generally accepted mechanism is the transition of an electron from a bound state to a free state, or from one free state in the neighbourhood of an ion to another free state of greater energy. The theory hitherto used is KRAMERS’ theory of the converse process of emission by a free electron passing a positive nucleus. Since emission and absorption are intimately connected by thermodynamics, the absorption coefficient can be calculated from KRAMERS’ formulae. Unfortunately, although KRAMERS’ work is in good agreement with laboratory observations of X-rays, it gives an absorption coefficient many times smaller than that found from astronomical observations. KRAMERS used classical electromagnetism, and got over the difficulty of the quantisation of negative energies by distributing the classical emission that involved captures somewhat arbitrarily among the various stationary states. It was evidently desirable to do the same work by means of quantum theory, both for the sake of greater rigour, and in the hope of finding a larger absorption. The foundations of such a theory were laid by OPPENHEIMER,|| upon the bed-rock of SCHRODINGER’s equation, in a paper to which this one is much indebted. The matrix-elements involving positive energies present considerable difficulty, and the approximations used by OPPENHEIMER in his paper of 1927 are unsuitable for stellar applications.

THEORY OF THE PRESSURE-INDUCED ROTATIONAL SPECTRUM OF HYDROGEN

1959 ◽  
Vol 37 (10) ◽  
pp. 1187-1198 ◽  
Author(s):  
J. Van Kranendonk ◽  
Z. J. Kiss
Keyword(s):  
Experimental Data ◽  
Distribution Function ◽  
Absorption Coefficient ◽  
Pair Distribution Function ◽  
Wave Functions ◽  
Rotational Line ◽  
Induction Effect ◽  
Rotational Spectrum ◽  
Absorption Coefficients ◽  
Good Agreement

The theory of induced infrared absorption developed previously is applied to the pressure-induced rotational spectrum of hydrogen. The intensity of the rotational band is due mainly to the quadrupolar induction effect, and to a small interference effect between the quadrupolar and overlap moments. From the experimental data on the binary absorption coefficients, values of the angle-dependent overlap moments are obtained for H2–He, H2–H2, H2–Ne, H2–N2, and H2–A. A calculation of the overlap moment for pure H2 is presented. Rosen-type wave functions appear to be inadequate for a calculation of the small angle-dependent rotational as well as vibrational overlap moments. The temperature dependence of the binary absorption coefficient is calculated, taking into account the quantum effects in the pair distribution function, and found to be in good agreement with the experimental data. The dependence on the ortho–para ratio is also discussed. The double rotational line S(1) + S(1) has been observed and its intensity measured.

Optical Absorption In Hg1−xCdxTe

1997 ◽  
Vol 484 ◽  
Author(s):  
Vaidya Nathan
Keyword(s):  
Experimental Data ◽  
Optical Absorption ◽  
Band Structure ◽  
Absorption Coefficient ◽  
Numerical Results ◽  
Recent Experimental Data ◽  
Narrow Gap ◽  
Interband Transitions ◽  
Linear Absorption Coefficient ◽  
Linear Absorption

AbstractThe theory of optical absorption due to interband transitions in direct-gap semiconductors is revisited. A new analytical expression for linear absorption coefficient in narrow-gap semiconductors is obtained by including the nonparabolic band structure due to Keldysh and Burstein-Moss shift. Numerical results are obtained for Hg1−xCdxTe for several values of x and temperature, and compared with recent experimental data. The agreement is found to be good.

scholarly journals Determination of the quasi-TE mode (in-plane) graphene linear absorption coefficient via integration with silicon-on-insulator racetrack cavity resonators

2014 ◽  
Vol 22 (15) ◽  
pp. 18625 ◽  
Author(s):  
Iain F Crowe ◽  
Nicholas Clark ◽  
Siham Hussein ◽  
Brian Towlson ◽  
Eric Whittaker ◽  
...  
Keyword(s):  
Absorption Coefficient ◽  
Silicon On Insulator ◽  
Linear Absorption Coefficient ◽  
Linear Absorption ◽  
Cavity Resonators ◽  
Te Mode
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