Risks and Realities

Radiation

Understanding Radiation in Your Life, Your World.

United States

Environmental Protection Agency

EPA-402-K-07-006 

May 2007

Office of Air and Radiation

Office of Radiation and Indoor Air

RESOURCES FOR

RADIATION INFORMATION

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Overview

 For additional radiation information, please visit our website: www.epa.gov/radiation

It’s natural and all around us. It comes up from the ground, 

down through the atmosphere, and even from within our own 

bodies. It can be man-made too. But it’s nothing new. It’s been 

present since the birth of the planet. It’s radiation, and radiation 

is, quite simply, part of our lives.

Naturally-occurring radioactive materials were discovered 

in 1896. Less than 40 years later, physicists discovered that 

radioactive elements can be artificially created. Within a 

decade of this discovery, scientists had split the atom.

These findings allow us to use radioactive materials for 

beneficial purposes, such as generating electricity and 

diagnosing and treating medical problems. For these many 

benefits, excessive radiation exposure can also threaten our 

health and the quality of our environment.

We cannot eliminate radiation from our environment. We can, 

however, reduce our risks by controlling, to some extent, our 

exposure to it. This booklet presents the major sources and 

uses of radiation, the risks from exposure, and how we can 

limit and reduce these risks.
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Matter is composed of atoms. Some atoms are unstable. As unstable atoms 

change and become more stable, they give off invisible energy waves or particles 

called radiation. 

There are different types of radiation, some more energetic than others. One type 

of radiation, non-ionizing radiation, has enough energy to move atoms but not 

enough to alter them chemically, like microwaves, radio waves and visible light. 

This booklet discusses the most energetic form, known as ionizing radiation. 

Ionizing radiation is capable of removing electrons from atoms and damaging 

living cells and the DNA of those cells. From here on ionizing radiation will be 

referred to simply as radiation. 

In the United States, we measure radiation doses in units called rem. Under the 

metric system, dose is measured in units called sieverts. One sievert is equal to 

100 rem. In this document millirems are used when talking about dose. A millirem 

is one thousandth (1/1000) of a rem. 

Scientists estimate that the average person in the United States receives a dose 

of about 360 millirem of radiation per year. Eighty percent of that exposure comes 

from natural sources – radon gas, the human body, outer space, and rocks and 

soil. The remaining 20 percent comes from man-made radiation sources, primarily 

medical x-rays.

Risks from Exposure to Radiation 

Radiation is known to cause cancer in humans. Radiation can also cause other 

adverse health effects, including genetic defects in the children of exposed 

parents or mental retardation in the children of mothers exposed during 

pregnancy. The risk of these other effects is much less than the risk of developing 

cancer due to radiation exposure. 

What is Ionizing Radiation?
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Gastrointestinal series

1,400 millirem 

(single procedure)

Radon in average home 

200 millirem

(annual)

Cosmic radiation living

in Denver

50 millirem

(annual)

Natural radioactivity

in the body

40 millirem

Mammogram (annual)

30 millirem

(single procedure)

Cosmic radioactivity

27 millirem

(annual)

Cosmic radiation living

at sea level

24 millirem (annual)

Chest x-ray

4 millirem

(single procedure)

Living near a nuclear 

power station

< 1 millirem on average 

(annual)

Diagnostic radiology 

50 millirem

(annual)

Terrestrial radioactivity

28 millirem 

(annual)

200

1,400

100

50

RELATIVE DOSES FROM RADIATION SOURCES

Millirem Doses
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Much of our knowledge about the risks from radiation is based on studies of more 

than 100,000 survivors of the atomic bombs at Hiroshima and Nagasaki and of 

people receiving large doses of medical radiation. In these studies, scientists 

observed health effects across a wide range of radiation doses, including single 

doses comparable to an average person’s lifetime dose from naturally-occurring 

background radiation (about 20,000 millirem). We learned many things from 

these studies. 

The most important are:

 The more radiation dose a person receives, the greater the chance of 

 developing cancer.

 It is the chance of cancer occurring, not the severity of cancer, that increases 

 as the radiation dose increases.

 Radiation induced cancers do not appear until years after the radiation dose 

 is received.

 The risk from radiation exposure will vary among individuals.

Current evidence suggests that any exposure to radiation poses some risk, however, 

risks at very low exposure levels have not been definitively demonstrated. While 

experts disagree over the definition of “low dose,”radiation protection measures 

are based on an assumption that even small amounts of radiation exposure may 

pose some small risk. Factoring in the entire dose of natural background radiation 

accumulated over a lifetime, the risk of developing cancer as a result of this exposure 

is estimated to be roughly 1 in 100. The additional contribution from all man-made 

sources of radiation is much smaller. It should be noted that all of the long-term 

health effects associated with exposure to radiation can also occur in people due to 

other causes.
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Naturally-occurring radiation accounts for approximately 80 percent of our exposure. 

Most of our exposure is from indoor radon, followed by radiation from outer space 

and from the Earth’s crust.

Natural Radiation

Radon

Approximately 55 percent of our exposure to radiation comes from radon. Radon is 

a colorless, odorless, tasteless radioactive gas, which comes from the natural decay 

of radium that is found in nearly all rock and soils. Radon usually moves from the 

ground up and migrates into homes and other buildings through openings in any 

ground contact floor or wall. Buildings trap radon inside, where it accumulates and 

may become a health hazard. Any home or building may have a radon problem, 

including new and old homes, well-sealed and drafty homes, and homes with or 

without basements. 

Radon is the second leading cause of lung cancer in the United States. EPA’s risk 

model predicts 20,000 Americans die each year from radon-related lung cancer, 

though the actual number could be somewhat higher or lower. Only smoking causes 

more lung cancer deaths and smokers exposed to radon are at an even higher risk 

than nonsmokers. 

Radon in the air is measured in picocuries per liter (pCi/L). 1.25 pCi/L is the national 

average for radon levels in homes. Where radon levels are 4 pCi/L or higher, the U.S. 

Environmental Protection Agency and the U.S. Surgeon General recommend that 

homeowners take action to reduce the radon level. It is estimated that nearly one in 

15 American homes has a radon level that should be reduced. Testing your home is 

the only way to know.

Controlling the Risks from Radon Exposure

Testing for radon is easy and only takes a few minutes. There are many kinds of lowcost, “do-it-yourself ” radon test kits available by phone, online and in many retail
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outlets. You can also hire a professional to do the testing. If an elevated radon level 

is detected in your home, you can reduce it in a variety of ways. Short of building 

your house with radon protection in mind, the preferred radon reduction technique is 

an active soil depressurization (ASD) system. Installation also requires the sealing of 

unwanted entry points for the ASD system to function effectively. An ASD system is 

basically a vent pipe with an inline centrifugal fan that operates continuously to vent 

radon (and other soil gases) from beneath the house. 

EPA leads the national commitment to educate citizens about residential radon 

risks. To achieve this goal, the Agency coordinates regional and state-level efforts to 

reduce exposure to radon. ormation about 

Radiation from the Ground and from Space

Radon is not the only source of naturally-occurring radioactivity. We receive about 

eight percent of our total exposure to natural background radiation from other 

radioactive elements in Earth’s crust, such as thorium and potassium. Radiation 

levels from these sources vary in different areas of the country.

Another eight percent of our radiation exposure comes from cosmic radiation from 

the sun, our galaxy, and other galaxies. Exposure to cosmic radiation depends, in 

part, on the elevation of where we live. For example, people who live in Denver, 

Colorado, which is more than 5,000 feet above sea level, are exposed to more 

cosmic radiation than people living in Chicago, Illinois, which is approximately 700 

feet above sea level. Exposure to cosmic radiation increases as you rise above sea 

level. Chicago’s thicker atmosphere filters out more cosmic radiation than Denver’s 

thinner atmosphere.

For more information about radon, its risks, and what you can do to protect yourself, 

or to request a free copy of EPA’s “A Citizen’s Guide to Radon,” call the National 

Radon Hotline at 1-800-SOS-RADON or contact your state’s radon office.
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Man-Made Radiation

Radiation in Medicine

Radiation used in medicine is the largest source of man-made radiation to which 

people in the United States are exposed. The majority of our man-made radiation 

exposure is from diagnostic x-rays. Physicians use x-rays in more than half of all 

medical diagnoses to determine the extent of disease or physical injury. In the field 

of nuclear medicine, radioactively labeled compounds (radiopharmaceuticals) are 

also used to support diagnoses.

Another source of radiation exposure is radiation therapy. One-third of all successful 

cancer treatments involve radiation. Precisely targeted radiation destroys 

cancerous cells while limiting damage to nearby healthy cells. In nuclear medicine, 

radiopharmaceuticals can also be used to treat tumors. For example, radioactive 

iodine will concentrate in the thyroid gland and can be used to treat thyroid tumors.

Controlling the Risks of Medical Radiation

The Nuclear Regulatory Commission (NRC), the Food and Drug Administration 

(FDA) and other federal and state agencies regulate medical procedures that use 

radiation. These agencies also issue guidance designed to reduce unnecessary 

use of radiation in diagnosis and treatment and ensure that technicians, equipment, 

and techniques meet standards for minimizing radiation exposure. Since any 

radiation exposure may carry some risk, it is necessary to decide whether the 

benefits of radiation justify its use. Health care providers must make the decision to 

use radiation on a case-by-case basis. Before receiving x-rays or any other type of 

medical treatment involving radiation exposure, you may want to discuss the need 

for and benefits of the procedure and its alternatives with your physician.

Since the discovery of radiation, people have benefited from the use of radiation in 

medicine and industry. Man-made sources of radiation account for about 20 percent 

of our total exposure to radiation.

MEDICINE
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Nuclear Power

Nuclear power reactors, which use uranium, supply the United States with about 20 

percent of its electricity. Nuclear power plant operations account for less than onehundredth (1/100) of a percent of the average American’s total radiation exposure. 

Controlling the Risks from Nuclear Materials

Existing radiation standards have been developed by a number of regulatory 

authorities, can come with a variety of units and are set at different levels for different 

issues. What they all have in common is the objective to reduce radiation exposure as 

much as practical. For example, radiation exposures to workers are allowed at levels 

significantly higher than for exposure to the public from releases to the environment. 

Although the radiation exposures differ, in both cases exposures are controlled to 

levels that are as low as reasonably achievable under the circumstances.

In 1979, EPA issued environmental standards designed to protect the public from 

radiation from nuclear energy. Additionally, in 1987, EPA issued guidance for 

federal agencies to use in the development of radiation exposure standards for 

workers. These standards limit the amount of radiation that workers in medicine, 

nuclear power, industry, mining, and waste management may receive. The Nuclear 

Regulatory Commission (NRC) is the federal agency responsible for implementing 

some of EPA’s radiation exposure standards and regulating nuclear power reactors 

and other uses of nuclear materials. The Department of Energy (DOE) also 

implements these standards at their facilities.

All domestic nuclear power plants must have emergency plans for protecting the 

public from radiation exposure from the potential release of radioactive material 

into the environment. EPA developed guidance for exposure levels at which actions 

are recommended to protect the public. State and local governments retain primary 

responsibility for protecting the public and the environment during radiological 

NUCLEAR POWER
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emergencies. Several federal agencies also respond to radiological emergencies, 

including EPA, the NRC, and the Departments of Homeland Security, Energy, 

Agriculture, and Health and Human Services. 

Radioactive Waste

Any activity that produces or uses radioactive material generates radioactive waste 

that must be disposed of properly. Radioactive waste can be in liquid or solid form, 

and its level of radioactivity can vary. Mining, nuclear power generation, and various 

industrial processes, defense weapons production, nuclear medicine, and scientific 

research all can produce radioactive waste. Items and equipment used during 

these types of industrial processes and research activities, such as rags, glassware, 

plastic bags, protective clothing, tools, and machinery, can become contaminated 

with radioactive material and must be disposed of as radioactive waste. Radioactive 

waste can remain radioactive for anywhere from days to hundreds or even thousands 

of years. Waste not properly isolated from the public and the generally accessible 

environment may contaminate air, soil, and water supplies.

Controlling the Risks of Radioactive Waste

Federal agencies and some states control the risks associated with radioactive waste 

by establishing standards and regulations that disposal facilities must meet so the 

waste is effectively isolated. For example, EPA is responsible for setting generally 

applicable environmental standards for disposal of radioactive waste. The federal 

government is continually investigating new technologies and disposal methods to 

effectively manage, treat, and dispose of radioactive waste.

 
10.

Conclusion

Natural sources of radioactivity are all around, and man-made radioactive materials 

are a vital part of medicine and industry. Exposure to some radiation, natural or manmade, is inevitable. We live with radiation everyday, therefore we must understand 

both its risks and benefits. 
11.

Many federal agencies and the states maintain important roles 

in protecting the public and the environment from radiation. 

States

The states have agencies responsible for regulating the use of radiation and for 

addressing radiation questions and problems. Your respective state agency is the best 

first-source of information about radiation issues affecting you. The states regulate 

the use of x-ray machines. Some are also responsible for regulating other sources of 

radiation within their state on behalf of federal agencies, such as NRC.

U.S. Environmental Protection Agency (EPA)

EPA issues standards and guidance to limit human exposure to radiation. EPA works 

with the public, industry, the states, and other government agencies to inform people 

about radiation’s risks and promote actions that reduce human exposure. EPA 

measures environmental levels of radiation and assesses radiation’s effects on people 

and the environment.

U.S. Nuclear Regulatory Commission (NRC)

NRC implements standards for protecting the public from radiation. NRC regulates 

the civilian uses of nuclear materials in the United States by: licensing facilities that 

possess, use, or dispose of nuclear materials; establishing standards governing the activities of 

licensees; and inspecting licensed facilities to ensure compliance with its requirements. These 

regulatory functions relate to both nuclear power plants and to other users of nuclear 

materials for purposes including nuclear medicine at hospitals, academic activities at 

educational institutions, research work, and industrial applications such as gauges and 

testing equipment.

U.S. Department of Homeland Security (DHS)

In the event of a terrorist attack, natural disaster or other large-scale emergency, 

the Department of Homeland Security has primary responsibility for ensuring that 

emergency response professionals are prepared. DHS coordinates the comprehensive 

federal response to any large-scale crisis and mounts a swift recovery effort. 

Additionally, DHS educates citizens to prepare themselves, their families and homes 

for major emergencies.
12.

U.S. Department of Health and Human Services (HHS)

HHS’s Food and Drug Administration’s Center for Devices and Radiological 

Health establishes standards for x-ray machines and other electronic products to 

ensure that human health is protected through the safe operation of these radiation 

producing devices.

U.S. Department of Energy (DOE)

DOE is responsible for the development of the disposal system for spent nuclear 

fuel from the nation’s civilian nuclear power plants. This activity is totally funded 

by a tax paid by the users of nuclear-generated electricity. DOE is also responsible 

for the management and disposal of nuclear waste and other radioactive materials 

associated with nuclear weapons production at federally-owned facilities. The 

Department of Energy is working to clean up its present and former nuclear sites. 

DOE is cooperating with state governments and private industry to clean up other 

locations around the United States that were contaminated with radiation as a result 

of government programs. DOE provides technical advice and assistance to states and 

the private sector in the management and disposal of low-level radioactive waste.

U.S. Department of Defense (DOD)

While DOE is responsible for the safe handling of radioactive material at defense 

production facilities, DOD is responsible for the safe handling and storage of nuclear 

weapons in its custody and for other military uses of nuclear energy.

U.S. Department of Transportation (DOT)

DOT, in cooperation with NRC and the states, governs the packaging and 

transport of radioactive materials. The Department also regulates carriers of 

radioactive materials.

Occupational Safety and Health Administration (OSHA)

OSHA, a division of the U.S. Department of Labor, develops and enforces regulations 

to protect workers not covered by other agencies from radiation exposure.

SHA

For additional radiation information, please 

visit our website: www.epa.gov/radiation