All gamma-ray sources for radiography are supplied in hermetically sealed, corrosion resistant source holders (capsules), made out of monel, vanadium or titanium. The Atomic Energy Authority in the country of origin encapsulates the radioactive materi- al. The supplier will supply the source with a certificate which indicates the type of source, its serial number, the activity at a certain date, and a disintegration graph.
The radiation material proper, also called the source or pellet, ranges in size from 1 to 4 mm. The size is dictated by the specific radiation activity of the source material. The outside dimensions of the cylindrical capsule are approximately 5.5 x 15 mm, as shown in figure 9-5.