Skip to main content
U.S. flag

An official website of the United States government

Here’s how you know

Dot gov

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

HTTPS

Secure .gov websites use HTTPS
A lock (LockA locked padlock) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

    • Environmental Topics
    • Air
    • Bed Bugs
    • Cancer
    • Chemicals, Toxics, and Pesticide
    • Emergency Response
    • Environmental Information by Location
    • Health
    • Land, Waste, and Cleanup
    • Lead
    • Mold
    • Radon
    • Research
    • Science Topics
    • Water Topics
    • A-Z Topic Index
    • Laws & Regulations
    • By Business Sector
    • By Topic
    • Compliance
    • Enforcement
    • Laws and Executive Orders
    • Regulations
    • Report a Violation
    • Environmental Violations
    • Fraud, Waste or Abuse
    • About EPA
    • Our Mission and What We Do
    • Headquarters Offices
    • Regional Offices
    • Labs and Research Centers
    • Planning, Budget, and Results
    • Organization Chart
    • EPA History

Breadcrumb

  1. Home
  2. RadTown
  3. Outdoors
  4. The Park

Background Radiation

Radiation Facts
  • Radionuclides can occur naturally or can be man-made.
  • Natural radiation sources contribute over half of the annual radiation exposure for an average person in the United States.

Radiation is a part of our day-to-day lives. It is a part of the air we breathe, the water we drink and the food we eat. 

On this page:
  • About Background Radiation
  • What you can do
  • Where to learn more


About Background Radiation

Background radiation is the radiation that is present in the natural environment. Natural background radiation is all around us, all of the time. It makes up over half of our yearly exposure to radiation. The amount of background radiation is different at every location. It depends on many factors, including:

diagram of background ecosystems
This image shows the different pieces of an ecosystem and the different things that could affect it, like solar radiation, disturbances, nutrients, minerals, and organisms.
Source: U.S. National Park Service (NPS)
  • Radionuclides present in Earth’s crust.
  • Radionuclides created by cosmic rays hitting atoms in Earth’s atmosphere. If we are closer to outer space, we are more likely to interact with these radionuclides.
  • Human activity and industry, including byproducts and wastes from processes like water filtration and treatment.
  • Weather, which can help radionuclides from nuclear weapons testing settle back to Earth from the atmosphere.

Scientists study ecosystems to learn how minerals and other chemicals, like radionuclides, move through Earth’s different natural systems. This research is called ecosystem science. Ecosystem science studies every part of the system, including the interactions between water, air, land, plants, animals, and humans. Scientists study radionuclides as they move through ecosystems.

Radionuclides in Earth’s Crust

Some radionuclides have been present in rocks since the formation of the Earth. All radionuclides go through radioactive decay until they reach a stable state. Radioactive decay is the process in which a radioactive element turns into another element, releasing radiation in the process. Natural radionuclides found in the Earth’s crust include uranium and thorium. As they decay, they become other radionuclides such as radium and radon. These radionuclides end up naturally in soil, water and air.

This is an image of background layers of the earth. Clicking on this image links to a larger version of the image.

Rocks containing natural radionuclides are broken down into soil by the weather, bacteria and fungi. When radionuclides are in soil particles, they can be blown around by wind. Some radionuclides dissolve in water and end up in surface or groundwater.

More than half of the average annual radiation exposure of people in the United States comes from natural sources. The natural radionuclide radon, which is produced from the decay of uranium and thorium, is the largest natural source of exposure. Radon is a natural radioactive gas that gets into homes and buildings. It is important to test your home for radon to reduce your exposure to radiation. Learn more about RadTown’s Radon in Homes, Schools and Buildings.

Radiation from Space

About 5% of the average annual radiation exposure for people in the United States comes from outer space. Our solar system’s sun, and other stars in the galaxy, emit a constant stream of cosmic radiation, which then regularly hits the Earth. When cosmic rays collide with atoms, they can make atoms radioactive. These radioactive atoms are called cosmogenic radionuclides. They are rare, but some of them do reach Earth’s surface and mix with soil and water. Learn more about Cosmic Radiation.

Cosmic radiation is the main source of carbon-14, which is used to date ancient artifacts. This technique is called carbon dating.

Radionuclides from Human Uses of Radioactive Material

Most radioactive material in the environment comes from natural sources. Much smaller amounts of radionuclides come from sources developed by humans. For example, uranium mines, nuclear power plants, and research facilities that use radionuclides sometimes add small amounts of radionuclides to the ecosystem. For most people, the annual exposure from these sources is very low. There may be a serious health hazard only in certain areas where open uranium, hard rock metal mines, other mineral mines or mining wastes are present.

  • Nuclear weapons testing: Mostly in the 1950s and 1960s, nuclear weapons tests released large amounts of radionuclides that spread and remained in ecosystems until the radionuclides decayed away. The Comprehensive Nuclear-Test Ban Treaty Organization (CTBTO) has a network of radionuclide monitoring stations that detect radionuclide particles and noble gases, like xenon, which would indicate a nuclear test.
  • Nuclear facility releases: The small amounts of airborne radionuclides released from facilities that handle and process radioactive materials can get into the soil, water or air. The EPA regulates how much radioactive materials can be released from these facilities. Learn more about Nuclear Power Plants.
  • Radioactive waste: Improper disposal of radioactive waste is another way radionuclides can enter an ecosystem. For example, water seeping thorough mining wastes can dissolve some radionuclides and carry them into the water system. Public water systems are carefully monitored by your state, and must meet federal standards, to make sure the drinking water is safe.

What You Can Do

  • Get your water tested for radionuclides. If you use water from a private well, you should get your water tested for radionuclides. Learn more about Natural Radionuclides in Private Well.
  • Test your home for radon. Testing at home is easy. Many kinds of low-cost radon test kits are available by phone, online and in stores. If you prefer, you can also hire a professional to do the testing. Learn more about radon, its risk and what you can do to protect yourself, on the EPA’s Radon website.

Where to Learn More

The U.S. Environmental Protection Agency (EPA)

The EPA develops standards for disposal of nuclear waste and, in some cases, oversees the disposal of radioactive material. The EPA's National Emissions Standards for Hazardous Air Pollutants for Radionuclides, or Radiation NESHAPs, sets regulatory limits for radionuclide emissions from industrial sources. The EPA also creates guidance for radon in homes, schools and businesses.

Radon
This website provides information about radon and the EPA’s radon protection activities.

RadNet
On this website, you can learn about RadNet, the EPA’s national network of radiation monitoring stations. RadNet regularly collects air, precipitation, drinking water samples to test for radioactivity.

Radiation: Facts, Risks and Realities
This document provides facts about ionizing radiation. It also discusses risks and benefits of using ionizing radiation.

Radiation NESHAPs
On this webpage, you can read a description of the EPA’s National Emissions Standards for Hazardous Air Pollutants, Radiation (NESHAPs). The webpage also provides links to more detailed information about NESHAPs.

Private Wells
If you have a well, you can find useful information on this webpage about keeping your water safe to drink.

Basic Information about Your Drinking Water
This page discusses the Safe Drinking Water Act (SDWA).

Radionuclides in Drinking Water
On this webpage, you can read about Safe Drinking Water Act radionuclide regulations.

The U.S. Nuclear Regulatory Commission (NRC)

The NRC regulates nuclear material, and researches human use of radioactive material.

Sources of Radiation
On this webpage you can see a chart of the public's exposure to ionizing radiation. It shows both natural and man-made sources.

Comprehensive Nuclear-Test-Ban Treaty Organization

CTBTO bans nuclear explosions by everyone, everywhere: on the Earth's surface, in the atmosphere, underwater and underground.        

Radionuclide Monitoring
This webpage explains the CTBTO’s radionuclide monitoring system.

RadTown

  • Neighborhood
    • School
      • Radioactive Material in Science Classrooms
      • Tritium in Exit Signs
    • House
      • Americium in Ionization Smoke Detectors
      • Microwave Ovens
      • Natural Radionuclides in Private Wells
      • Natural Radionuclides in Public Drinking Water
      • Radon in Homes, Schools and Buildings
    • Radiation in Medicine
      • Medical X-rays
      • Nuclear Medicine
      • Radiation Therapy
    • Electric and Magnetic Radiation
      • Electric and Magnetic Fields from Power Lines
      • Non-Ionizing Radiation From Wireless Technology
  • Outdoors
    • The Park
      • Background Radiation
      • Cosmic Radiation
      • Radiation from Solar Activity
      • Ultraviolet (UV) Radiation and Sun Exposure
    • Mines
      • Radioactive Material from Fertilizer Production
      • Uranium Mining and Milling
    • Construction Sites
      • Industrial Radiography
      • Natural Radioactivity in Building Materials
      • Nuclear Gauges
    • Waste Sites
      • Radioactive Material in Scrap Metal
      • Radioactive Waste
  • Waterfront
    • Power Generation
      • Nuclear Power Plants
      • Radiation Wastes From Coal-fired Power Plants
      • Radioactive Waste Material From Oil and Gas Drilling
    • Military Activities
      • Depleted Uranium
      • Nuclear Submarines and Aircraft Carriers
      • Radioactive Fallout From Nuclear Weapons Testing
    • Transporting Radioactive Material
      • Radiation and Shipping Port Security
      • Transportation of Radioactive Material
    • Cleanup Sites
      • Radioactively Contaminated Sites
  • Downtown
    • Radiation Science
      • Particle Accelerators
      • Radioactive Material Used in Research
    • Consumer Products
      • Mail Irradiation
      • Natural Radioactivity in Food
      • Radioactivity in Antiques
      • Radioactivity in Tobacco
      • Ultraviolet (UV) Tanning Equipment
    • Air Travel
      • Radiation and Airport Security Scanning
    • Emergency Response
      • Careers in Radiation Protection
      • Radiation Emergencies
  • Classroom Materials for Teachers
    • Radiation Protection
      • Teacher Information
      • Vocabulary Activities
      • Activity 1: History of Radiation Protection
      • Activity 2: Time, Distance and Shielding
      • Activity 3: Radiation Warning and Protection Equipment
      • Activity 4: Buildings as Shielding
      • Activity 5: A Career in Radiation Protection
      • Activity 6: Impact of Radiological Emergencies
      • Activity 7: Benefits of Radiation
    • The Radioactive Atom
      • Teacher Information
      • Vocabulary Activities
      • Activity 1: Atomic Discoveries
      • Activity 2: Atomic Math and Shorthand
      • Activity 3: Strong Nuclear Forces
      • Activity 4: Atomic Stability
      • Activity 5: Half-Life
      • Activity 6: Radioactive Decay Chain
    • Radiation Exposure
      • Teacher Information
      • Vocabulary Activities
      • Activity 1: Types of Radiation
      • Activity 2: Sources of Annual Radiation Exposure
      • Activity 3: Penetrating Powers of Ionizing Radiation
      • Activity 4: Exposure Pathways
      • Activity 5: Radiation Health Effects
      • Activity 6: Acute versus Chronic Exposure
    • Radon
      • Teacher Information
      • Vocabulary Activities
      • Activity 1: Ground Up
      • Activity 2: Radon Vacuum
      • Activity 3: Indoor Radon Levels
      • Activity 4: The Half-Life of Radon
    • Uranium
      • Teacher Information
      • Vocabulary Activities
      • Activity 1: Uranium, Radium and Radon
      • Activity 2: Radiation and Uranium Myths and Facts
      • Activity 3: Uranium Ore Sources in the U.S.
      • Activity 4: Uranium Mining Methods
      • Activity 5: Radiation Contamination and Exposure
      • Activity 6: Radiation Cleanup and Advocacy Objectives
  • A to Z Subject Index
  • Women in Radiation History
    • Lise Meitner
    • Chien-Shiung Wu
    • Rosalind Franklin
  • Glossary
Contact Us about RadTown
Contact Us to ask a question, provide feedback, or report a problem.
Last updated on March 28, 2025
  • Assistance
  • Spanish
  • Arabic
  • Chinese (simplified)
  • Chinese (traditional)
  • French
  • Haitian Creole
  • Korean
  • Portuguese
  • Russian
  • Tagalog
  • Vietnamese
United States Environmental Protection Agency

Discover.

  • Accessibility Statement
  • Budget & Performance
  • Contracting
  • EPA www Web Snapshot
  • Grants
  • No FEAR Act Data
  • Plain Writing
  • Privacy
  • Privacy and Security Notice

Connect.

  • Data
  • Inspector General
  • Jobs
  • Newsroom
  • Regulations.gov
  • Subscribe
  • USA.gov
  • White House

Ask.

  • Contact EPA
  • EPA Disclaimers
  • Hotlines
  • FOIA Requests
  • Frequent Questions
  • Site Feedback

Follow.