FLUORESCENT SCREEN (Salt Screen) (RT): Intensifying screens composed of fluorescent all, such as calcium
tungstate, which emit a visible blue-violet electromagnetic radiation when activated by the absorption of the primary
rays, thereby reducing the exposure time.
FLUORESCENT SCREENS (RT): Intensifying screens composed of fluorescent salts which emit a visible blue-violet
electromagnetic 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 that
fluoresces 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 exposed
to 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 I
square centimeter in 1 second.
FLUX DENSITY (MT): The number of magnetic flux lines per unit of area taken at right angles to the direction of
magnetic 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 explaining
the 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 gamma
source, and the film.
FOCAL SPOT (RT): The area on the target that receives the bombardment of electrons and emits the primary radiation
necessary to produce an image of the object on a radiographic film. The spot at which the sound beam from a focused
search 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 point
or 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 anything
other 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.