Ionizing Radiation


Ionizing radiation is the high-energy form of electromagnetic radiation found in x rays and Gamma rays. Ionizing radiation causes changes in living material. Ionizing radiation is both naturally occurring and can be constructed through man-made means.


According to the United Nations Scientific Committee on the Effects of Atomic Radiation, roughly 82% of the radiation all humans are exposed to is naturally occurring background radiation. The remaining 18% of radiation exposure comes from man-made sources, including medical x rays, nuclear medicine, consumer products, occupational hazards, fallout, and the nuclear fuel cycle.


Molecules are bound to each other, usually with an even number of electrons. The penetration of ionizing radiation causes the division of molecules. The result is atoms with unpaired electrons, which are commonly known as “free radicals.” The free radicals are then said to be “ionized”: they are very reactive and when in contact with macromolecules (like the DNA) of living cells, these free radicals can cause cell damage and cell death. Ionizing radiation is recognized as a carcinogen and is able to act on its own or in accordance with other carcinogens to cause cell mutations, cell damage, or cell death.

There are multiple units for measuring ionizing radiation. The roentgen (R), is the oldest unit used to measure charge under standard conditions. The grey (Gy) and the rad are the units used to measure the amount of radiation absorbed by living tissue. Finally, the sievert (Sv) and the rem are the units used to normalize doses of radiation based on relative biologic effectiveness (RBE).

All humans are exposed to certain levels of radiation, called background radiation. These types of radiation are naturally occurring and include cosmic radiation, radiation from elements in the Earth's surface, and radiation from atoms normally present in food or the air.

Survivors of nuclear disaster—including nuclear bombs—are especially susceptible to cell mutation, cell death, and the carcinogenic properties of ionizing radiation. The greater the dose of radiation an individual is exposed to, the greater the likelihood of cancer and death. Scientists have conducted research and concluded that this type of radiation exposure produces tendencies to certain types of cancers—like stomach, lung, and liver—more than others—like pancreas, prostate, and rectum.

Those suffering from certain medical conditions (especially conditions that are genetically inherited), are more susceptible to the damaging risks of ionizing radiation than the general population. A medical condition called ataxia telangiectasia (AT) is the most well known medical condition contributing to such a susceptibility to ionizing radiation. AT patients are especially susceptible to ionizing radiation and between 10–20% of AT patients contract cancer in their teens or early 20s.

The radiation used to treat cancerous tumors can cause additional damage to the body through its ionizing effects. Both bone and cartilage tissues can be damaged by cancer-treating radiation, resulting in fractures of the bone, which cannot always be prevented. These types of fractures are most common during radiation treatments to address cancerous tumors on the uterus or bladder. Patients suffering from these radiation-induced fractures will often feel the pain of the fracture before it can be detected by x ray.


Exposure to background radiation is universal and cannot be avoided. There are steps that can be taken, however, to reduce other exposure to ionizing radiation, thereby reducing the potential for the generation of free radicals and the subsequent health risks like cell damage, cell death, cancer, and death.

Medical exposures to ionizing radiation are the greatest man-made sources of ionizing radiation. The exposure of ionizing radiation from a 10 second chest x ray is 20,000 microsieverts; the exposure of ionizing radiation from a 20 second CT scan is 800,000 microsieverts. This is compared with the total dose rate from background radiation which is between 0.3 and 1.5 microsievert or the exposure from an airplane flight which is around 3 microsieverts. Therefore, minimizing unnecessary exposure to ionizing radiation associated with diagnostic tests like x rays and CT scans is desirable. These tests are often used more frequently than is necessary given the risk of ionizing radiation exposure. Before receiving such a diagnostic test, individuals should compare the risk of identifying a potential illness or injury being detected with the risks associated with the level of ionizing radiation to which they will be exposed during such a test. Until the causes of various forms of cancer are fully understood, preventing unnecessary exposure to all carcinogens—including ionizing radiation—may help reduce the likelihood of developing cancer.

The Occupational Safety & Health Administration (OSHA)—a division of the U.S. Department of Labor—has regulations in place to help protect individuals whose jobs put them in contact with sources of ionizing radiation. Additionally, 25 states, Puerto Rico, and the Virgin Islands have their own standards and policies of enforcements to help protect workers within their borders. These regulations also dictate how potentially dangerous materials and machinery should be handled, which helps reduce exposure to ionizing radiation for employees and the general public by standardizing necessary safety standards.

Effects on public health

Medical x rays and CT scans are necessary and life-saving diagnostic tools used around the world and particularly in the United States. The diagnostic capabilities of these tests save lives, detect injuries, and help doctors locate causes of illness and discomfort. The availability of this technology has caused these diagnostic tools to be relied upon heavily, often used before or in place of other diagnostic tools.

It is important that these tests remain readily available to assist in detecting disease and injury; however, it is also important to recognize the potential for adverse health risks posed by these tests. Better education and awareness is needed to help doctors and patients when making informed decisions regarding the necessity and frequency of using diagnostic tools that emit ionizing radiation.

Efforts and solutions

See also Cancer ; Radiation ; Radiation exposure .

Electromagnetic radiation (EMR)—
A type of energy that is both absorbed and emitted by particles. Forms of EMR demonstrate wave-like movement as they travel through space and can be measured along the electromagnetic spectrum based on the frequency of wavelengths of emitted light or energy. Forms of EMR include radio radiation, infrared radiation, light on the visible spectrum, ultraviolet light, x rays and Gamma rays.
To transform a molecule or atom—a neutral particle—into an ion—a particle with a positive or negative charge.



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American Cancer Society, 250 Williams Street NW, Atlanta, GA, USA, 30303, (800) 227-2345, .

Andrea Nienstedt, MA

  This information is not a tool for self-diagnosis or a substitute for professional care.