1. The compactness of a substance; the ratio of mass to unit volume, usually expressed as g/cm3 (kg/m3 in the SI system). 2. The quantity of electricity on a given surface or in a given time per unit of volume. 3. In radiological physics, the opacity to light of an exposed radiographic or photographic film; the darker the film, the greater the measured d. 4. In clinical radiology, a less-exposed area on a film, corresponding to a region of greater x-ray attenuation (radiopacity) in the subject; the more light transmitted by the film, the greater the d. of the subject; this is not actually the opposite of the prior definition, since one concerns film d. and the other subject d. [L. densitas, fr. densus, thick]
buoyant d. the d. that allows a substance to float in some standard fluid.
count d. photon d
flux d. 1. flux (4) 2. either particle flux d., the particle fluence rate, or energy flux d., the energy fluence rate of intensity. Cf. fluence.
incidence d. the person-time incidence rate.
optical d. (OD) absorbance
photon d. the number of counted events recorded in scintigraphy per square centimeter or per square inch of imaged area.count d;
spin d. the number of nuclear dipoles per unit volume.
vapor d. the mass per unit volume of a vapor; since the vapor d. changes with temperature and pressure, it is commonly expressed as a specific gravity, i.e., the weight of the vapor divided by the weight of an equal volume of a reference gas (e.g., oxygen or hydrogen) at the same temperature and pressure.
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