Figure 11-3.--Principle of X-ray generation.
(electrons) collide with a mass of matter. The
collision transforms the energy of motion (kinetic
energy) of the electron into radiant energy. The faster
the particles are moving, the shorter the wavelength
of the X rays. The greater the current (milliamperes),
the greater the intensity of the radiant energy
produced. Most of the kinetic energy is transformed
into heat. Only a small portion is transformed into
electromagnetic waves (X rays) with the ability to
travel in straight lines without displacing the matter
through which they pass.
Figure 11-2 shows how the several units of the
portable X-ray equipment are interconnected. You
Figure 11-4.--Shematic diagram for making a radiograph.
can find a complete description of this setup, as well
as the details for the operation and care of the
equipment, in the handbook furnished with the
increasing the effects of the X rays on the film. These
machine. This equipment should be operated only by
screens perform two functions. First, they absorb long
qualified personnel who have had the required special
rays from the X-ray tube and the scattered rays from the
training on this equipment.
object being radiographed and from the surrounding
area. Second, the primary X rays striking the screens
The diagram in figure 11-4 illustrates the
cause the screens to emit secondary rays that react on
fundamentals of radiographic exposure and the
the film in the same manner as do the primary rays. This
setup of the film, specimen, and radiation source.
intensifies the amount of radiation striking the film.
Note that the film assembly is placed as close as
The film and screens are packaged in a lightproof device
possible to the test specimen, while the X-ray
known as a cassette, which is positioned snugly against
source is some distance away. A definite space
the specimen that is to be radiographed.
ratio must be maintained between the specimen
and the X-ray source if a satisfactory radiograph is
to be obtained.
Many factors govern the results obtained in
Almost all industrial radiographs are made with
thickness of the test specimen, the type of film used,
lead intensifying screens. Normally, lead intensifying
the focal distance between the specimen and the
screens decrease the exposure time required by
radiation source, the voltage applied, the exposure