T.O. 33B-1-1Glossary 36FLUORESCENT SCREEN (Salt Screen) (RT): Intensifying screens composed of fluorescent all, such as calciumtungstate, which emit a visible blue-violet electromagnetic radiation when activated by the absorption of the primaryrays, thereby reducing the exposure time.FLUORESCENT SCREENS (RT): Intensifying screens composed of fluorescent salts which emit a visible blue-violetelectromagnetic radiation when activated by the absorption of the primary rays, thereby reducing the exposure time.FLUOROGRAPHY (RT): The use of photography to record fluoroscopic images on film.FLUOROMETALLIC SCREEN (RT): A screen consisting of a metal foil (usually lead) coated with a material thatfluoresces when exposed to ionizing radiation. It combines the properties of the fluorescent and metal screen.FLUOROSCOPY (RT): The visual observation on a fluorescent screen of the image of an object that has been exposedto penetrating, ionizing radiation.FLUX: A fusible salt mixture or gas used to purify molten metal by removing suspended oxides or dissolved gas.FLUX (NEUTRON): The intensity of neutron radiation. It is expressed as the number of neutrons passing through Isquare centimeter in 1 second.FLUX DENSITY (MT): The number of magnetic flux lines per unit of area taken at right angles to the direction ofmagnetic field flow. This is a measure of field strength.FLUX LINES (MT): Also called lines of force, magnetism or induction. Imaginary lines used as means of explainingthe distribution and potential of magnetic fields.FLUX, MAGNETIC LEAKAGE: See FIELD, LEAKAGE.FLUX PENETRATION (MT): The depth to which magnetic flux is effective in a part.FOCAL-FILM DISTANCE (FFD) (RT): The distance in inches between the focal spot of the X-ray tube, or gammasource, and the film.FOCAL SPOT (RT): The area on the target that receives the bombardment of electrons and emits the primary radiationnecessary to produce an image of the object on a radiographic film. The spot at which the sound beam from a focusedsearch unit converges to maximum intensity.FOCUSED BEAM (UT): Sound beam that converges to a focal spot.FOCUSED TRANSDUCER (UT): A transducer with a concave face which converges the acoustic beam to a focal pointor line at a definite distance from the face. Also known as a focused search unit.FOCUSING: Concentration or convergence of energy into a small beam.FOCUSING (RT): Concentration or convergence of energy into a narrow beam. FOD (RT): Film object distance;distance from film to object being radiographed.FOG (RT): A general term used to denote any increase in the optical density of a processed film caused by anythingother than the direct action of image-forming radiation.FOG DENSITY (RT): See FOG.FOG THRESHOLD (RT): The minimum uniform density inherent in a processed emulsion without prior exposure.
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