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Basic Processes of Interaction of Radiation with Matter
Published in Mikhail G. Brik, Chong-Geng Ma, Theoretical Spectroscopy of Transition Metal and Rare Earth Ions, 2019
Mikhail G. Brik, Chong-Geng Ma
It is widely used in spectroscopy to describe different absorption abilities of atoms. The absorption cross section has the dimension of area and can be thought of as an effective disk with an absorbing atom at the center (Fig. 2.10). This disk is in some sense a target, which absorbs the incident photons. If the photons passing near an absorbing atom miss these “disks,” there is no absorption. The absorption cross section can be also thought of as an effective area around an absorbing atom that extracts power from the incident light beam. Transitions between different energy levels can have different values of the absorption cross sections.
Fundamental Light–Tissue Interactions: Light Scattering and Absorption
Published in Vadim Backman, Adam Wax, Hao F. Zhang, A Laboratory Manual in Biophotonics, 2018
Vadim Backman, Adam Wax, Hao F. Zhang
The absorption coefficient μa is defined through the absorption cross-section of individual absorbing particles σa for a particulate medium, or as the absorption cross-section per unit volume when absorbing molecules are distributed throughout the medium and it is not convenient to talk about isolated absorbing particles μa=σaρN=σa,δVδV.
Local structure development: Characterization of biominerals using x-ray absorption spectroscopy
Published in Elaine DiMasi, Laurie B. Gower, Biomineralization Sourcebook, 2014
e most direct method to measure the absorption cross section is by measuring the intensity of transmission of an x-ray beam through the sample (It) and normalizing it to the incident beam (I0). Other more indirect methods are used to calculate absorption through measurements of relaxation processes like the total electron yield (TEY) or fluorescence yield (FLY). The choice of the detection method depends on many factors, but mostly on the geometry of the sample and the concentration of the absorbing element in the sample. Transmission measurements are usually fast and have the highest signal to noise ratio when the sample thickness (x) ful lls exp(-x0) 1 with respect to the absorber element of interest. When the sample contains other strongly absorbing elements, the total absorption should be taken into account, as it reduces the intensity of the
Benchmark Solutions for Radiative Transfer with a Moving Mesh and Exact Uncollided Source Treatments
Published in Nuclear Science and Engineering, 2023
William Bennett, Ryan G. McClarren
The variables in these equations are , the angular flux or intensity; the scalar flux; , the temperature; and , the material energy density. and have units of energy per area per time (GJ cm–2‧ns–1), and has units of energy density (GJ‧cm–3). is a source term with units of energy density per time. is the cosine of the particle direction with respect to the -axis. is the particle velocity, which is the speed of light in a vacuum for our application, cm‧ns–1. The radiation constant is GJ cm–3‧keV–4, where is the Stefan-Boltzmann constant. The absorption cross section is in units of inverse length.
Analytical, Semi-Analytical, and Numerical Heavy-Gas Verification Benchmarks of the Effective Multiplication Factor and Temperature Coefficient
Published in Nuclear Science and Engineering, 2018
Matthew A. Gonzales, Brian C. Kiedrowski, Anil K. Prinja, Forrest B. Brown
and K. As with the previous case, , cm. The functional dependence of the absorption cross section on the temperature is such that the absorption increases with temperature within the range describing the wings of the resonance, decreases in the range around the peak, and exhibits increases at lower temperatures and decreases at higher temperatures in the middle range. This temperature behavior is meant to represent an analogous effect to Doppler broadening, even though the precise behavior and values are not obtained through the convolution integral involved in the physical Doppler broadening process. Note that, as with the previous case, the dimensionless-energy bin boundaries given in Table III are at temperature and change with per Eq. (10) such that the cross sections are defined on a fixed energy grid.