Understanding NRT- Reading 1- 2 of 2- Radiogaphic Testing A

Man made sources are produced by introducing an extra neutron to atoms of
the source material. As the material rids itself of the neutron, energy is
released in the form of gamma rays.
Two of the more common industrial Gamma-ray sources are iridium-192 and
cobalt-60. These isotopes emit radiation in two or three discreet wavelengths.
■ Cobalt-60 will emit a 1.33 and a 1.17 MeV gamma ray, and
■ iridium-192 will emit 0.31, 0.47, and 0.60 MeV gamma rays.
Physical size of isotope materials will very from manufacturer, but generally
an isotope is a pellet 1.5 mm x 1.5 mm. Depending on the activity (curies)
desired a pellet or pellets are loaded into a stainless steel capsule and sealed
by welding. New sources of cobalt will have an activity of 20 curies, and new
sources of iridium will have an activity of 100 curies.
Charlie Chong/ Fion Zhang