Unique Properties of Gamma Rays
General. Gamma-ray radiography is basically the same as X-ray radiography. Differences in material properties and effects between X-rays and gamma rays are largely a matter of degree. The major advantage of using gamma rays is the fact that gamma ray sources are small and provide access to small spaces, thereby simplifying exposure technique. Exposure periods are, however, generally longer with gamma ray sources.
Sources Of Radiation. Many atoms exhibit a property called radioactivity, which is a phenomenon of spontaneous disintegration or decay. This characteristic is believed to be caused by the instability of the complex structure of the atom under the action of the electric, magnetic and gravitational forces existing within. Radium is one of the elements with a natural unbalance that releases energy in the form of gamma rays to achieve a more stable condition. In addition to the gamma rays, some alpha particles (helium nuclei) and beta particles (electrons) are allowed to escape. The alpha and beta particles are readily absorbed, but the gamma rays are more penetrating since their energy extends above 1,000,000 electron volts (eV). This energy release is uncontrolled and is a result of forces in the atom. Many of the atomic structures can be artificially made to release energy by subjecting them to strong fields of neutrons generated in nuclear reactors. These neutron fields add energy to the atom, which upsets the balance within the nucleus and causes the atom to emit one or more types of energy. Cobalt is one element commonly made artificially radioactive and used in NDI since the energy it releases is a very penetrating form of gamma rays.
