Radiation is a form of energy. There are two basic types of radiation. One kind is particulate radiation, which involves tiny fast-moving particles that have both energy and mass. Particulate radiation is primarily produced by disintegration of an unstable atom and includes Alpha and Beta particles.
Alpha particles are high energy, large subatomic structures of protons and neutrons. They can travel only a short distance and are stopped by a piece of paper or skin. Beta particles are fast moving electrons. They are a fraction of the size of alpha particles, but can travel farther and are more penetrating.
Particulate radiation is of secondary concern to industrial radiographers. Since these particles have weight and are relatively large, they are easily absorbed by a small amount of shielding. However, it should be noted that shielding materials, such as the depleted uranium used in many gamma radiography cameras, will be a source of Beta particles if the container should ever develop a leak. If a leak were to occur, the material could be transferred to the hands and other parts of a radiographer’s body, causing what is known as particulate contamination. This is the reason periodic “leak” and “wipe tests” are performed on equipment.
The second basic type of radiation is electromagnetic radiation. This kind of radiation is pure energy with no mass and is like vibrating or pulsating waves of electrical and magnetic energy. Electromagnetic waves are produced by a vibrating electric charge and as such, they consist of both an electric and a magnetic component. In addition to acting like waves, electromagnetic radiation acts like a stream of small "packets" of energy called photons. Another way that electromagnetic radiation has been described is in terms of a stream of photons. The massless photon particles each travel in a wave-like pattern. Each photon contains a certain amount (or bundle) of energy, and all electromagnetic radiation consists of these photons. The only difference between the various types of electromagnetic radiation is the amount of energy found in the photons. Electromagnetic radiation travels in a straight line at the speed of light (3 x 108 m/s).
Light waves, radio waves, microwaves, X-rays and Gamma rays are some examples of electromagnetic radiation. These waves differ in their wavelength as shown in the electromagnetic spectrum image above. Although all portions of the electromagnetic spectrum are governed by the same laws, their different wavelengths and different energies allow them to have different effects on matter. Radio waves, for example, have such a long wavelength and low energy that our eyes cannot detect them and they pass through our bodies. It takes a special antenna and electronics to capture and amplify radio waves.
The wavelength of visible light is on the order of 6,000 angstroms, while the wavelength of X-rays is in the range of one angstrom and that of Gamma rays is 0.0001 angstrom. This very short wavelength is what gives X-rays and Gamma rays their power to penetrate materials that light cannot. Unlike light, X- and gamma rays cannot be seen, felt, or heard. The fact that they cannot be detected with our normal human senses and can damage our cells is why they must be treated carefully.
Partial support for this work was provided by the NSF-ATE (Advanced Technological Eduaction) program through grant #DUE 0101709.
Opinions expressed are those of the authors and not necessarily those of the National Science Foundation.