We all encounter many forms of radiation every day. Some of these are naturally occurring, and some are manmade. Some are harmful, while others are not.
Select the links below to find out about sources of radiation in the environment.
Many forms of radiation are not harmful to life. Visible light is a good example. Infrared radiation, which we feel as heat, and radio waves, which we can't sense at all, are two others. These are all forms of electromagnetic radiation. Forms of electromagnetic radiation that can be harmful to life include ultraviolet, x-rays, and gamma radiation.
Microwaves, though less energetic than light waves, can heat tissue by causing water molecules within the tissue to vibrate rapidly (this is how microwaves are used to heat food), but microwaves do not have enough energy to affect chemical bonds unless they heat the material enough to cause thermal damage. Ultraviolet light, x-rays, and gamma rays can also damage tissue, but they do so by breaking the chemical bonds within cells, including those that hold DNA together.
The sun, powered by nuclear fusion, emits radiation that is both necessary and harmful to life on Earth. Light and infrared radiation (heat) are needed by almost all of Earth's life forms. The atmosphere filters out much of the harmful radiation emitted by the sun, though some radiation, such as ultraviolet light, does pass through. UV radiation can damage living tissues and cause cancer.
Gamma radiation in high doses is potentially lethal to life on Earth, but the sun releases relatively little gamma radiation. The gamma radiation created deep within the sun is absorbed and re-emitted by other atoms as it works its way toward the surface. By the time it leaves the sun's surface, most of it is no longer high-energy gamma rays but other forms of electromagnetic radiation.
Nuclear fission is a useful energy source because of its ability to create heat and sustain a chain reaction. Unfortunately, fission produces waste products that are radioactive, including cesium-137 and strontium-90. Strontium-90 emits powerful beta radiation, which is a spray of negatively charged electrons.
Most of the radioactivity in spent nuclear fuel is in the form of strontium-90 and cesium-137. These atoms are unstable and decay to other atoms through the emission of high-energy gamma rays. Strontium-90 and cesium-137 are chemically separated from the spent fuel and sold to various companies.
Although most of the radioactive substance tritium (an isotope of hydrogen) is created naturally by cosmic ray interactions, slightly higher concentrations of the element have been found in the waters surrounding nuclear reactors that use uranium-238 as a fuel and "heavy water" as a coolant. Tritium emits beta radiation, which sprays negatively charged electrons.
When tritium decays, one of its neutrons turns into a proton. The change from neutral state to positive causes the neutron to emit an electron. With two protons rather than one, the atom becomes a helium atom. This type of decay is known as beta-minus decay because it emits a negative electron. Beta-plus decay occurs when a proton turns into a neutron, which causes the emission of a positively charged electron (a positron).
The Earth contains various forms of naturally occurring radioactive sources, including uranium, potassium, and carbon. One of the products of uranium decay is the gas radon, which sometimes collects inside enclosed spaces, such as homes. Radon decays quickly by alpha decay and can easily find its way into the body through inhalation. Prolonged exposure to high levels of radon may cause lung cancer.
When the atom decays, a particle consisting of two protons and two neutrons—a helium nucleus—shoots out of the nucleus of the radioactive atom. Once it leaves the atom, it often picks up two free electrons and becomes a helium atom. An alpha particle doesn't travel very far: a single sheet of paper or the dead outer layer of your skin cells will stop it.
In addition to alpha radiation, naturally radioactive elements in the Earth also emit gamma and beta radiation.
There are several potential sources of radiation inside the house. One is radon-222, which can seep from soil and concrete and into the house. (For more about radon, see Radioactivity in the Earth.) Others include smoke detectors (americium), watches (tritium), and even you (carbon-14 and potassium-40).
Radioactivity within the House
There's radioactive material within your body—carbon-14 and potassium-40—but no one knows for sure if these elements pose a great threat to health. If natural radiation does hurt health, the effects are so small that they have been impossible to measure. Moreover, there's little understanding of how the human body repairs radiation damage or what stimulates or degrades the repair process.
Earth's atmosphere protects us from cosmic radiation—fast-moving particles such as protons—that come from the sun and from outside the solar system. Like other forms of harmful radiation, cosmic radiation can damage cells by breaking the chemical bonds within cells.
Some of these particles, which can travel at speeds close to that of light, make their way to Earth's surface, but most collide with the atoms and molecules in the atmosphere long before they reach the surface. These collisions produce a shower of fragments that then rain down toward the surface.
Although it's not commonly done and is, in fact, against the law, the disposal of radioactive materials at landfills not licensed for radioactive waste does occur. Sometimes material is thrown out inadvertently. For example, a lost or stolen medical or industrial instrument containing cesium-137 may be found by someone unaware of its radioactivity and brought to a landfill.
Unlike beta and alpha particles, gamma rays have great penetrating ability.
electron: a particle with a negative charge, often found near an atom's nucleus; carrier of beta-minus radiation
positron: an electron with a positive charge; carrier of beta-plus radiation
photon: a massless particle that travels at the speed of light; carrier of electromagnetic radiation
proton: a particle with a positive charge, often found inside the nucleus of an atom
neutron: a particle with no electrical charge, often found within the nucleus of an atom
nucleus: the central region of an atom, made up of protons and neutrons (nuclei are more than one nucleus)
Radiation is the emission of particles or electromagnetic waves.
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