How Are People Exposed to X-rays and Gamma Rays?

People may be exposed to this type of radiation from 3 main sources:

  • Natural background radiation comes from cosmic rays from our solar system and radioactive elements normally present in the soil. This is the major contributor to worldwide radiation exposure.
  • Medical radiation is used for x-rays, CT scans, and other tests, as well as for radiation therapy. Radiation therapy is used to treat some types of cancer and involves dosages many thousand times higher than those used in diagnostic x-rays.
  • Non-medical, man-made radiation is used in small amounts in food irradiation, airport security scanners, and some consumer products. Exposure to man-made radiation can happen in certain workplaces, or in communities as a result of above ground nuclear weapons testing and nuclear accidents.

Natural background Radiation

We are all exposed to some amount of radiation just from being on this planet. This is known as background radiation. In the United States this averages about 3 mSv per year. For most people, background radiation accounts for most of their exposure to ionizing radiation during the year. It comes from several different sources.

Cosmic rays

Cosmic rays are radioactive particles that hit the earth from outer space. They come from the sun and from other stars. The earth’s atmosphere blocks a portion of these rays, but some of them reach the ground.

Because the atmosphere blocks some cosmic rays, exposure is greater at higher altitudes. For example, people who live in Denver, Colorado, which is at a high elevation, are exposed to slightly more cosmic rays than people living at sea level. People are also exposed to higher levels of cosmic rays during airplane flights. Airline pilots and flight attendants, who spend many hours at high elevations, are exposed to more of these rays, but it is not clear if they have an increased risk of cancer because of it.

Radiation in the earth

People are also exposed to small amounts of radiation from radioactive elements that occur naturally in rocks and soil. Some of these may end up in building materials used in houses and other structures. Tiny amounts of radiation may even be found in drinking water and in some plant-based foods as a result of being in contact with the soil. For people who smoke, tobacco can account for a significant portion of the yearly radiation they receive.

Radon

The largest source of natural background radiation for most people is radon. This is an odorless, colorless gas that is formed from the breakdown of radioactive elements in the ground. Radon levels are usually higher inside buildings and homes, especially in levels closer to the ground such as basements. Radon levels can vary a great deal, depending on where you live or work. For example, exposure is higher for people who work in mines. For more detailed information on radon and its possible health effects, see Radon.

Medical radiation

X-rays, gamma rays, and other forms of ionizing radiation are used to diagnose and treat some medical conditions. This can be in the form of radiation that penetrates from outside the body, or radioactive particles that are swallowed or inserted into the body.

Imaging tests

Certain types of imaging tests, such as x-rays, CT scans, and nuclear medicine tests (such as PET scans and bone scans) expose people to low levels of radiation in order to create internal pictures of the body. (Some imaging tests, such as MRI and ultrasound do not expose people to ionizing radiation.)

In adults: The amount of radiation varies depending on the test. For example, the exposure from a 2-view chest x-ray is about 0.1 mSv, while exposure from a regular chest CT is about 7 or 8 mSv. The exposure from a PET/CT scan (which combines a PET scan of the body with a CT scan) can be as high as 30 mSv. Fluoroscopy, which uses x-rays to make real-time moving images, is like getting many x-rays in a row. It exposes people to different amounts of radiation depending on how long it is used. The amount of radiation used in many imaging tests has gone down over time as technology has improved.

In children: Radiation exposure also varies based on the test. Unless the settings on the scanner are adjusted for body size, exposure levels can be higher than they would be for an adult. For example, one study found that an abdominal CT may expose an adult’s stomach to about 10 mSv, while a newborn baby’s stomach would be exposed to 20mSv by getting the same test without the settings adjusted.

For children, exposure to radiation from imaging tests is of particular concern, because:

  • Children are much more sensitive to radiation than adults
  • Children are expected to live longer than adults, so they have a longer time to develop problems from radiation exposure
  • With tests like CT scans, children might receive a higher radiation dose than necessary if the CT settings are not adjusted for their smaller body size

These factors mean that for a young child, the risk of developing a radiation-related cancer could be several times higher than for an adult exposed to the same imaging test. The risks from these tests are not known for sure, but to be safe, most doctors recommend that children only get these tests when they are absolutely needed. When such tests are done, it is important to use the minimum amount of radiation needed to get the image.

Radiation therapy

X-rays, gamma rays, and other forms of ionizing radiation offer an effective way to treat certain kinds of cancer. During radiation therapy, high doses of ionizing radiation (much higher than those used for imaging tests) are directed at the cancer, resulting in the death of the cancer cells. However, this can lead to DNA mutations in other cells that survive the radiation, which may eventually lead to the development of a second cancer. Radiation therapy is also sometimes used to treat serious medical conditions besides cancer.

For more information about cancer risks from radiation therapy for cancer, see Second Cancers in Adults.

Non-medical sources of man-made radiation

People may also be exposed to ionizing radiation from non-medical man-made sources.

Nuclear weapons

The atomic bombs dropped on Nagasaki and Hiroshima, Japan exposed many people to radiation from x-rays, gamma rays, and neutrons. Some people died fairly quickly as a result of burns and radiation sickness, but many survived. The survivors were exposed to different amounts of radiation, depending largely on how far they were from the explosions. Only about 2% of the survivors were exposed to high amounts of radiation (1000 mSv or more), while almost one-third were exposed to doses that are relatively low (less than 5 mSv). Much of the information that we have about radiation and cancer risks comes from studies of more than 105,000 of the survivors.

The United States government conducted above-ground nuclear tests in the South Pacific and in the state of Nevada between 1945 and 1962. Other countries also conducted above-ground tests. Many people in the military at the time were part of training exercises in the area and were exposed to ionizing radiation from these tests. Others were exposed to radiation while working at facilities making the bombs or at other nuclear sites.

Non-military people living near or downwind of nuclear test sites may have also been exposed to radioactive byproducts. Levels of radiation are likely to be higher near these sites, but some radioactive particles from the tests entered the atmosphere and traveled great distances, landing thousands of miles away from the original site. While exposure levels were likely to be higher at the time of testing, some radiation in the soil today is the result of these tests.

Programs have been set up to give financial support to people who were exposed to nuclear weapons testing and developed cancer. 

Nuclear power plants

Emissions of radiation from nuclear power plants are carefully monitored and controlled. According to the Environmental Protection Agency (EPA), nuclear power plant operations account for less than one-hundredth (1/100) of a percent of the average American’s total radiation exposure.

Nuclear power plant accidents: Accidents at nuclear power plants are rare, but they have the potential to expose people to high levels of radiation.

In 1986, an accident at the nuclear power plant at Chernobyl (in Ukraine) exposed millions of people living in the area to radiation, either directly or from radioactive elements released into the air that ended up deposited on the ground. The emergency clean-up workers were exposed to the highest levels of radiation. Although the average dose to clean-up workers was about 100 mSv, some were exposed to very high doses – more than 1000 mSv. The average doses to people living in the area (some of whom were evacuated) ranged from 10 to 50 mSv.

In 2011, an earthquake and tsunami struck the coast of Japan that resulted in damage to the Fukushima Dai-ichi Nuclear Power Plant in Fukushima Prefecture, Japan. Radiation was released into the air, contaminating soil, food, and water (both fresh and seawater). Within the plant, radiation levels reached as high as 10,000 mSv per hour early on. An area of more than 300 square miles around the plant was also found to be contaminated with radiation, although at lower levels than within the plant. Because of high radiation levels, many areas were evacuated. The health effects of this disaster are still being studied.

Workplace exposures

Some people can be exposed to radiation at work. For example:

  • People who work in nuclear power plants may be exposed to higher levels of radiation than the general public, although their exposure levels are monitored carefully.
  • People who work in uranium mines are monitored because of their exposure to radiation in the form of radon.
  • People who work in health or dental care, particularly those who work with x-ray (or other imaging test) equipment or who work with radioactive isotopes, may also be exposed to radiation at work. Radiation exposure may also occur at some research labs.

In the United States, people who are likely to be exposed to radiation in the workplace are monitored carefully. Exposure is limited to an effective dose of 100 mSv over 5 years, with a maximum of 50 mSv in any single year.

Consumer products

Some consumer products contain small amounts of ionizing radiation.

For example, tobacco products contain low levels of radiation, which may come from the soil it’s grown in or the fertilizer used to help it grow. Tobacco may account for a significant portion of the yearly radiation that people who smoke are exposed to.

Some building materials used in the home or other structures may contain low levels of naturally occurring radiation. The amount of radiation can vary depending on what they’re made of, but the levels are unlikely to contribute much to a person’s overall exposure to radiation, according to the EPA.

Many smoke detectors contain a small amount of a very low-level radioactive material that helps detect the smoke. This material is sealed in a container and does not pose a significant risk of radiation exposure.

Food irradiation

Ionizing radiation can be used to kill bacteria and other germs on certain foods, which may make them safer to eat and help them last longer. Some people may be concerned that irradiated food may itself contain radiation.

It’s important to understand that the radiation does not stay in the food. According to the United States Department of Agriculture (USDA), irradiating food does not cause it to become radioactive and does not change nutritional value of the food any more than cooking or freezing it might.

Airport security scanners

In recent years, some airports have begun to use whole body scanners as a way to detect objects hidden by clothing. These scanners are different from the metal detectors most people are familiar with.

The type of body scanner currently in use is based on millimeter wave technology. Neither millimeter wave scanners nor metal detectors expose people to x-rays or gamma rays.

Another type of body scanner, based on backscatter technology, used very weak x-rays aimed at the surface of the body to capture a whole body image. These scanners are no longer in use.

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

American College of Radiology. 2010. ACR Statement on Airport Full-body Scanners and Radiation. Accessed at www.acr.org/About-Us/Media-Center/Position-Statements/Position-Statements-Folder/ACR-Statement-on-Airport-Full-body-Scanners-and-Radiation on February 10, 2015.

Brenner DJ, Hall EJ. Computed tomography--an increasing source of radiation exposure. N Engl J Med. 2007;357:2277-2284.

Cardis E, Howe G, Ron E, et al. Cancer consequences of the Chernobyl accident: 20 years on. J Radiol Prot. 2006;26:127-140.

National Toxicology Program. Ionizing radiation: x-radiation and gamma radiation. Rep Carcinog. 2011;12:237-240.

National Cancer Institute. Radiation Risks and Pediatric Computed Tomography (CT): A Guide for Health Care Providers. 6/7/2012. Accessed at www.cancer.gov/cancertopics/causes/radiation/radiation-risks-pediatric-CT on March 22, 2013.

Ozasa K, Shimizu Y, Sakata R, et al. Risk of cancer and non-cancer diseases in the atomic bomb survivors. Radiat Prot Dosimetry. 2011;146:272-275.

Transportation Security Administration. AIT: Frequently Asked Questions. 4/26/2014. Accessed at www.tsa.gov/ait-frequently-asked-questions on February 10, 2015.

United States Department of Agriculture. Irradiation and Food Safety Answers to Frequently Asked Questions. 8/9/2013. Accessed at http://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-safety-fact-sheets/production-and-inspection/irradiation-and-food-safety/irradiation-food-safety-faq on February 9, 2015.

Zablotska LB, Bazyka D, Lubin JH, et al. Radiation and the risk of chronic lymphocytic and other leukemias among Chernobyl cleanup workers. Environ Health Perspect. 2013 Jan;121(1):59-65. Epub 2012 Oct 24.

References

American College of Radiology. 2010. ACR Statement on Airport Full-body Scanners and Radiation. Accessed at www.acr.org/About-Us/Media-Center/Position-Statements/Position-Statements-Folder/ACR-Statement-on-Airport-Full-body-Scanners-and-Radiation on February 10, 2015.

Brenner DJ, Hall EJ. Computed tomography--an increasing source of radiation exposure. N Engl J Med. 2007;357:2277-2284.

Cardis E, Howe G, Ron E, et al. Cancer consequences of the Chernobyl accident: 20 years on. J Radiol Prot. 2006;26:127-140.

National Toxicology Program. Ionizing radiation: x-radiation and gamma radiation. Rep Carcinog. 2011;12:237-240.

National Cancer Institute. Radiation Risks and Pediatric Computed Tomography (CT): A Guide for Health Care Providers. 6/7/2012. Accessed at www.cancer.gov/cancertopics/causes/radiation/radiation-risks-pediatric-CT on March 22, 2013.

Ozasa K, Shimizu Y, Sakata R, et al. Risk of cancer and non-cancer diseases in the atomic bomb survivors. Radiat Prot Dosimetry. 2011;146:272-275.

Transportation Security Administration. AIT: Frequently Asked Questions. 4/26/2014. Accessed at www.tsa.gov/ait-frequently-asked-questions on February 10, 2015.

United States Department of Agriculture. Irradiation and Food Safety Answers to Frequently Asked Questions. 8/9/2013. Accessed at http://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-safety-fact-sheets/production-and-inspection/irradiation-and-food-safety/irradiation-food-safety-faq on February 9, 2015.

Zablotska LB, Bazyka D, Lubin JH, et al. Radiation and the risk of chronic lymphocytic and other leukemias among Chernobyl cleanup workers. Environ Health Perspect. 2013 Jan;121(1):59-65. Epub 2012 Oct 24.

Last Revised: February 24, 2015

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