This unit of temperature is still used customarily in the United States.
Definition: 0° is the coldest temperature achieved by using an ice and salt mixture, and 100° is set at the temperature of the human body. On this scale, the freezing point of water turned out to be about 32°F and the boiling point about 212°F.
1°F equals 5/9°C. To convert a temperature in °F to the Celsius scale, first subtract 32° and then multiply by 5/9. In the other direction, to convert a temperature in °C to the Fahrenheit scale, multiply by 9/5 and then add 32°. The unit was defined by the German physicist Daniel Gabriel Fahrenheit.

See also Kelvin, Celsius.

(FNAA) See Neutron Activation Analysis.

(FOV) The field of view is the maximum diameter of the area of the scanned object that is represented in the reconstructed image. It can also be the surface of the used detector.

The filament is the source of electrons (cathode) in x-ray tubes. A thin wire (0.1- 0.5 mm, usually tungsten) emits electrons due to thermionic emission, operating in a vacuum and energized with electric current.
A CT tube utilizes a larger filament with larger size of the effective focal spot than a conventional x-ray tube.

A film consists of a thin, transparent sheet of polyester or similar material. Films are coated on one or both sides with an emulsion sensitive to radiation, light or heat. Films are relatively radiolucent due to their relatively low atomic number (that of silver halide).

See also X-Ray Film, Direct Exposure Film and Intensifying Screen.