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In physics, absorption cross-section is a measure of the probability of an absorption process. More generally, the term cross-section is used in physics to quantify the probability of a certain particle-particle interaction, e.g., scattering , electromagnetic absorption , etc. (Note that light in this context is described as consisting of ...
In biochemistry, the molar absorption coefficient of a protein at 280 nm depends almost exclusively on the number of aromatic residues, particularly tryptophan, and can be predicted from the sequence of amino acids. [6] Similarly, the molar absorption coefficient of nucleic acids at 260 nm can be predicted given the nucleotide sequence.
In physics, the cross section is a measure of the probability that a specific process will take place in a collision of two particles. For example, the Rutherford cross-section is a measure of probability that an alpha particle will be deflected by a given angle during an interaction with an atomic nucleus.
Although absorption is rather low in this spectral range, it still contributes to the overall attenuation of tissue. Figure 3: The molar extinction coefficients of eumelanin and pheomelanin. [5] Other tissue components with less significant contributions to the total absorption spectrum of tissue are melanin and fat.
Nuclear cross sections are used in determining the nuclear reaction rate, and are governed by the reaction rate equation for a particular set of particles (usually viewed as a "beam and target" thought experiment where one particle or nucleus is the "target", which is typically at rest, and the other is treated as a "beam", which is a projectile with a given energy).
The absorption neutron cross section of an isotope of a chemical element is the effective cross-sectional area that an atom of that isotope presents to absorption and is a measure of the probability of neutron capture. It is usually measured in barns. Absorption cross section is often highly dependent on neutron energy. In general, the ...
The oscillator strength is defined by the following relation to the cross section for absorption: [19] = =, where e {\displaystyle e} is the electron charge, m e {\displaystyle m_{e}} is the electron mass, and ϕ ν {\displaystyle \phi _{\nu }} and ϕ ω {\displaystyle \phi _{\omega }} are normalized distribution functions in frequency and ...
σ λ is their absorption cross-section at wavelength λ (units: area) B λ (T) is the Planck function for temperature T and wavelength λ (units: power/area/solid angle/wavelength - e.g. watts/cm 2 /sr/cm) I λ is the spectral intensity of the radiation entering the increment ds with the same units as B λ (T)