Ionizing radiation is high-energy radiation, such as X-rays, gamma rays and alpha, beta and neutron particles, that can remove electrons from atoms and damage living tissue and DNA.
Ionizing radiation is radiation with enough energy to remove tightly bound electrons from atoms, creating charged particles called ions. When this happens in the human body, it can damage cells and DNA directly or through chemical reactions that follow. High doses received over a short time can cause radiation burns and acute radiation sickness, while lower doses received over time increase the risk of cancer.
Ionizing radiation comes in several forms: alpha particles, beta particles, gamma rays, X-rays and neutrons. It is produced by radioactive materials as they decay and by machines such as X-ray units and particle accelerators. Everyone is exposed to some natural background radiation from the earth, cosmic rays and radon gas, but certain jobs can add significantly to that dose.
Ionizing radiation is distinct from non-ionizing radiation, such as radio waves, microwaves, visible light, infrared and most ultraviolet light, which does not carry enough energy to ionize atoms. Non-ionizing radiation can still cause harm, such as burns or eye damage, but it is controlled differently.
Alpha particles are heavy and travel only a few centimeters in air. A sheet of paper or the outer layer of skin stops them. They are mainly a hazard when alpha-emitting materials, such as radon decay products or certain uranium compounds, are inhaled or swallowed and come into direct contact with living tissue.
Beta particles are lighter and more penetrating. They can travel several meters in air and penetrate skin, causing burns at high exposures. Plastic, glass or a thin sheet of aluminum usually provides adequate shielding.
Gamma rays and X-rays are high-energy electromagnetic radiation. They can pass through the body and require dense shielding such as lead, steel or thick concrete. They are the main external radiation hazard in most workplaces.
Neutrons are produced in nuclear reactors, some industrial gauges and certain research facilities. They are highly penetrating and are best shielded by materials rich in hydrogen, such as water, concrete or polyethylene.
In the United States, the Nuclear Regulatory Commission (NRC) regulates radioactive materials from nuclear reactors and their byproducts, and many states, known as Agreement States, run equivalent programs under agreement with the NRC. States also typically regulate X-ray machines and naturally occurring radioactive materials. OSHA's ionizing radiation standards, 29 CFR 1910.1096 for general industry and 1926.53 for construction, cover exposures not regulated by the NRC or an Agreement State.
Under the NRC's 10 CFR Part 20, the annual occupational dose limits for adults include:
OSHA's older standard uses quarterly limits, such as 1.25 rem per calendar quarter to the whole body, with some flexibility based on a worker's dose history.
Dose limits are a ceiling, not a target. Radiation protection programs follow the ALARA principle, keeping exposures As Low As Reasonably Achievable. NRC licensees are required to use procedures and engineering controls to achieve ALARA doses.
The three basic protective measures are minimizing time near a source, maximizing distance, since dose rate drops sharply as distance increases, and placing appropriate shielding between people and the source.
These include shielded rooms and enclosures, interlocks on X-ray equipment, warning lights and signs, restricted and controlled areas, written procedures, source inventories and security, and leak testing of sealed sources. The hierarchy of controls applies here as it does to any hazard.
Workers likely to receive significant doses wear personal dosimeters, such as badges or electronic dosimeters, and area monitoring and survey meters are used to check dose rates. Records of individual doses must be kept. For internal hazards, bioassays or air sampling may be used, often as part of a broader industrial hygiene program.
Workers must be trained in the hazards, the protective measures and emergency procedures. Licensees designate a radiation safety officer who oversees the program.
A road construction contractor used nuclear moisture-density gauges, which contain small sealed sources of cesium-137 and americium-beryllium, to test soil compaction. A gauge left on the tailgate of a pickup was run over by a compactor, damaging the housing. The technician, unsure what to do, picked up the gauge and put it in the truck cab to bring it back to the yard.
The company's radiation safety officer was called and immediately had the area around the damaged gauge cordoned off, surveyed the gauge and the truck with a survey meter, and reported the incident to the state radiation control program as required. Fortunately, the sources remained intact and there was no contamination. The investigation led to refresher training on gauge emergency procedures, a rule that gauges are never set down on the ground or tailgates near heavy equipment, emergency instruction cards in every gauge case, and a survey meter assigned to each crew that uses gauges.
Ionizing radiation has enough energy to remove electrons from atoms and damage DNA directly. Non-ionizing radiation, such as radio waves, microwaves, visible light and most ultraviolet, has less energy. It can still cause harm, such as burns or eye injuries, but it does not ionize atoms.
Not always. Under NRC rules, monitoring is required for adults likely to receive more than 10% of the annual dose limits, among other criteria. Many employers issue dosimeters more widely to confirm exposures remain low.
Yes. Radon is a naturally occurring radioactive gas that can accumulate in underground mines, basements, tunnels and some buildings. It is a leading cause of lung cancer. Testing and ventilation are the main controls.
Keep people away from the area, do not handle the source, and contact your radiation safety officer immediately. Lost, stolen or damaged sources must be reported to the NRC or the state radiation control program within specified time frames.
Part of SafetyIQ's EHS glossary: plain-English definitions of workplace health and safety terms.
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