FILM SPEED (RT): A measure of the rate at which a film responds to a given amount of radiation. Slower films
require a longer period of time to reach the same film density than a fast film under the same exposure conditions.
FILM UNSHARPNESS (RT): See UNSHARPNESS.
FILM VIEWER (RT): See FILM ILLUMINATOR.
FILTER (RT): A layer of absorptive material which is placed in the beam of radiation for the purpose of absorbing rays
of long wavelengths to control the quality of the radiograph.
FILTERS (UT, ET): Filters are electrical circuits designed to eliminate various frequencies from a circuit output or
input. Filter may be low pass (high frequencies suppressed), high pass (low frequencies suppressed) or band pass
(frequencies outside a specified range suppressed).
FILTRATION: See INHERENT FILTRATION.
FILTRATION (RT): The use of a filter to alter the characteristics of a radiation beam.
FINE CRACK: A discontinuity in a solid material with a very fine opening to the surface, but possessing length and
depth greater than the width of this opening; usually depth is many times the width.
Surface condition, quality or appearance of a metal.
Stock on a forging to be removed when finish machined.
FIRE SCALE: Oxide subscale formed just under the surface of certain alloys when they are annealed in air.
FISH EYES: Areas on a fractured steel surface having a characteristic white crystalline appearance.
FISSION: The splitting of a heavy nucleus into two roughly equal parts (which are nuclei of lighter elements)
accompanied by the release of a relatively large amount of energy and frequently one or more neutrons. Fission can
occur spontaneously, but usually it is caused by the absorption of gamma rays, neutrons, or other particles.
FISSION PRODUCTS: Nuclei formed by the fission of heavy elements. They are of medium atomic weight, and
almost all are radioactive. Examples: strontium-90, cesium-137.
FISSIONABLE MATERIAL: Any material readily fissioned by slow neutrons, for example, uranium-235 and
FIT: The amount of clearance or interference between mating parts.
FIXER (RT): A chemical solution that removes unexposed silver halide crystals from film emulsion.
FIXING (RT): The procedure used in film processing that removes all of the undeveloped silver salts of the emulsion
from the surface of the film, thus leaving only the developed latent image.
FLAME HARDENING: A method of hardening where the surface layer is heated by a high temperature torch and then
FLAKES: Short discontinuous internal fissures in ferrous metals attributed to stresses produced by localized
transformation and decreased solubility of hydrogen during cooling after hot working. In a fractured surface, flakes