Understanding Neutron Radiography Reading V-Kodak Part 2 of 3

Film Graininess, Screen Mottle
(See also "Film Graininess; Signal-to-Noise Ratio in Radiographs".)
The image on an x-ray film is formed by countless minute silver grains, the
individual particles being so small that they are visible only under a
microscope. However, these small particles are grouped together in relatively
large masses, which are visible to the naked eye or with a magnification of
only a few diameters. These masses result in the visual impression called
graininess. All films exhibit graininess to a greater or lesser degree.
In general, the slower films have lower graininess than the faster. Thus, Film
Y (Figure 47) would have a lower graininess than Film X.
The graininess of all films increases as the penetration of the radiation
increases, although the rate of increase may be different for different films.
The graininess of the images produced at high kilovoltages makes the slow,
inherently fine-grain films especially useful in the million- and multimillion-volt
range. When sufficient exposure can be given, they are also useful with
gamma rays.
Charlie Chong/ Fion Zhang
Radiography in Modern Industry. Rochester, NY: Eastman Kodak Co. 1980