A radiological hazard is defined as an unintentional exposure to materials that emit ionizing radiation.
The primary radiological hazard is the health effects resulting from unintentional exposure to ionizing radiation. When radiation interacts with atoms, energy is deposited, resulting in ionization (electron excitation). This ionization may damage certain critical molecules or structures in a cell. Ionizing radiation is emitted from molecular elements generally referred to as radio nuclides, and this radiation has the ability to alter in varying amounts the function of living processes at the cellular level. Types of ionizing radiation include Alpha particles, Beta particles, Gamma rays, X-rays, and Neutron particles.
Radiation is measured in different ways. Measurements used in the United States include Roentgen, radiation absorbed dose (RAD), and roentgen equivalent man (REM). The term RAD is being replaced by the International System skin dose unit for radiation absorbed dose, the gray (Gy) which is a measurement of absorbed dose in any material. 1 Gy = 100 RAD.
Radiation effects fall into two broad categories:
- Direct effect on cells (direct impact with a particularly sensitive atom or molecule in a cell).
- Indirect effect on cells (interaction with water molecules in the body where the deposited energy in the water leads to the creation of unstable, toxic hyperoxide molecules which then damage sensitive molecules and afflict subcellular structures).
The nature and extent of damage caused by ionizing radiation depend on a number of factors including the amount of exposure (energy strength), the frequency and/or duration of exposure, and the penetrating power of the radiation to which an individual is exposed. Acute exposure to very high doses of ionizing radiation is rare but can cause death within a few days or months. The sensitivity of the exposed cells also influences the extent of damage. For example, rapidly growing tissues, such as developing embryos, are particularly vulnerable to harm from ionizing radiation.
Nuclear power plants are a significant potential source of ionizing radiation. The health and environment impacts from the Three-Mile Island and Chernobyl, Russia disasters illustrate the potential hazards from nuclear power plants. Other sources of ionizing radiation include medical and diagnostic X-ray machines, certain surveying instruments, some imaging systems used to check pipelines, radioactive sources used to calibrate radiation detection instruments, and even some household fire detectors.
On December 7, 1979, following the March 1979 Three Mile Island nuclear power plant accident in Pennsylvania, President Carter transferred the Federal lead role in off-site radiological emergency planning and preparedness activities from the Nuclear Regulatory Commission (NRC) to Federal Emergency Management Agency (FEMA). FEMA established the Radiological Emergency Preparedness (REP) Program to (1) ensure that the public health and safety of citizens living around commercial nuclear power plants would be adequately protected in the event of a nuclear power station accident and (2) inform and educate the public about radiological emergency preparedness. FEMA's REP Program responsibilities encompass only "off-site" activities, that is State and local government emergency preparedness activities that take place beyond the nuclear power plant boundaries. Onsite activities continue to be the responsibility of the NRC.
The U.S. Department of Energy (DOE) occasionally transports radioactive material through Minnesota via road and rail. In 1999 there were 21 such shipments (14 via rail and 7 via road). Information on these shipments can be located at the Office of Transportation.
University laboratories, medical treatment facilities and medical laboratories also contain a large number of radionuclides. These materials are used in research, diagnostics and treatment.