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Absorbance is defined as "the logarithm of the ratio of incident to transmitted radiant power through a sample (excluding the effects on cell walls)". [1] Alternatively, for samples which scatter light, absorbance may be defined as "the negative logarithm of one minus absorptance, as measured on a uniform sample". [2]
The SI unit of molar absorption coefficient is the square metre per mole (m 2 /mol), but in practice, quantities are usually expressed in terms of M −1 ⋅cm −1 or L⋅mol −1 ⋅cm −1 (the latter two units are both equal to 0.1 m 2 /mol). In older literature, the cm 2 /mol is sometimes used; 1 M −1 ⋅cm −1 equals 1000 cm 2 /mol.
In physics, the D-region of Earth's ionosphere is known to significantly absorb radio signals that fall within the high-frequency electromagnetic spectrum. In nuclear physics, absorption of nuclear radiations can be used for measuring the fluid levels, densitometry or thickness measurements. [2]
Absorption spectroscopy is performed across the electromagnetic spectrum. Absorption spectroscopy is employed as an analytical chemistry tool to determine the presence of a particular substance in a sample and, in many cases, to quantify the amount of the substance present.
The process is described by the Einstein coefficient (m 3 J −1 s −2), which gives the probability per unit time per unit energy density of the radiation field per unit frequency that an electron in state 1 with energy will absorb a photon with an energy E 2 − E 1 = hν and jump to state 2 with energy .
Absorption is a condition in which something takes in another substance. [1] In many processes important in technology, the chemical absorption is used in place of the physical process, e.g., absorption of carbon dioxide by sodium hydroxide – such acid-base processes do not follow the Nernst partition law (see: solubility).
However, there is also a specific, quantitative definition of "opacity", used in astronomy, plasma physics, and other fields, given here. In this use, "opacity" is another term for the mass attenuation coefficient (or, depending on context, mass absorption coefficient , the difference is described here ) κ ν {\displaystyle \kappa _{\nu }} at ...
Absorbed dose is a dose quantity which is the measure of the energy deposited in matter by ionizing radiation per unit mass.Absorbed dose is used in the calculation of dose uptake in living tissue in both radiation protection (reduction of harmful effects), and radiology (potential beneficial effects, for example in cancer treatment).