| attenuation | <radiobiology> Process by which a beam of radiation is reduced in intensity when passing through material - combination of absorption and scattering processes, leading to a decrease in flux density of beam when projected through matter. (16 Dec 1997) |
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| attenuation coefficient | 1. <radiobiology> Compton: The fractional number of photons removed from a beam of radiation per unit thickness of material through which it is passing as a result of Compton effect interactions. 2. Linear: The fractional number of photons removed from a beam of radiation per unit thickness of material through which it is passing due to all absorption and scattering processes. 3. Pair Production: That fractional decrease in the intensity of a beam of ionising radiation due to pair production in a medium through which it passes. 4. Photoelectric Effect: That fractional decrease in the intensity of a beam of ionising radiation due to photoelectric effect in a medium through which it passes. (16 Dec 1997) |
| attenuation compensation | In ultrasonography, an increase in receiver gain with time to compensate for loss in echo amplitude with depth, usually due to attenuation. Synonym: attenuation compensation, depth compensation, time compensation gain, time-compensated gain, time-varied gain control, time-varied gain. (05 Mar 2000) |
| attenuation factor | <radiobiology> A measure of the opacity of a layer of material for radiation transversing it, the ratio of the incident intensity to the transmitted intensity. It is equal to Io/I, where Io and I are the intensities of the incident and emergent radiation, respectively. In the usual sense of exponential absorption (I = Ioe- m x), the attenuation factor is e- m x, where x is the thickness of the material and m is the absorption coefficient. (16 Dec 1997) |
| mass attenuation coefficient | <physics> The mass attenuation coefficient, u/p, of a material for uncharged ionising particles is the quotient of DN/N by pdl, where DN/N is the fraction of particles that experience interactions in traversing a distance dl in a material of density p. (16 Dec 1997) |
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