Radiation protection: introduction
Ionizing radiation is radiation that has enough energy to cause ionization in matter, and when it passes through the tissues of the body it has sufficient energy to damage DNA (Hall, 1994). Examples are α-particles (helium nuclei), β-particles (electrons or positrons), γ-rays, X-rays and neutrons. While there are many benefits to the use of X-rays, radioisotopes, and other radioactive materials in industry, research, and power generation, their use entails exposure of personnel from normal use as well as accidents. Though some small amounts of radioisotopes are used in manned space missions for instrument calibration and research, the vast majority of crew exposures are due to the environment in which they work.
Whether an activity is controlled by the Nuclear Regulatory Commission (NRC), the Department of Energy (DOE), or the Occupational Safety and Health Administration (OSHA), an operational radiation protection program is required so that doses to personnel and members of the public are monitored and documented in order that exposures may be kept at a minimum. NASA's program includes active and passive personnel dosimetry, vehicle shielding design requirements, as well as real-time active monitoring of the heliosphere to watch for changes in the environment that would be indicative of an impending solar particle event (SPE).
When considering the amount of radiation absorbed by living tissue, the standard unit known as the gray (Gy) is employed, in which 1 Gy equals 1 J of radiation energy absorbed per kilogram of tissue (the older unit of 1 rad = 0.01 Gy).