Radiation is energy. It can come from unstable atoms that undergo radioactive decay, or it can be produced by machines. Radiation travels from its source in the form of energy waves or energized particles. There are different forms of radiation and they have different properties and effects.

Non-Ionizing and Ionizing Radiation

There are two kinds of radiation: non-ionizing radiation and ionizing radiation.

Non-ionizing radiation has enough energy to move atoms in a molecule around or cause them to vibrate, but not enough to remove electrons from atoms. Examples of this kind of radiation are radio waves, visible light and microwaves.

Ionizing radiation has so much energy it can knock electrons out of atoms, a process known as ionization. Ionizing radiation can affect the atoms in living things, so it poses a health risk by damaging tissue and DNA in genes. Ionizing radiation comes from x-ray machines, cosmic particles from outer space and radioactive elements. Radioactive elements emit ionizing radiation as their atoms undergo radioactive decay.

Radioactive decay is the emission of energy in the form of ionizing radiation. The ionizing radiation that is emitted can include alpha particles, beta particles and/or gamma rays. Radioactive decay occurs in unstable atoms called radionuclides.

Electromagnetic Spectrum

The energy of the radiation shown on the spectrum below increases from left to right as the frequency rises.

EPA’s mission in radiation protection is to protect human health and the environment from the ionizing radiation that comes from human use of radioactive elements. Other agencies regulate the non-ionizing radiation that is emitted by electrical devices such as radio transmitters or cell phones (See: Radiation Resources Outside of EPA).

Types of Ionizing Radiation

Alpha Particles

Alpha particles (α) are positively charged and made up of two protons and two neutrons from the atom’s nucleus. Alpha particles come from the decay of the heaviest radioactive elements, such as uranium, radium and polonium. Even though alpha particles are very energetic, they are so heavy that they use up their energy over short distances and are unable to travel very far from the atom.

The health effect from exposure to alpha particles depends greatly on how a person is exposed. Alpha particles lack the energy to penetrate even the outer layer of skin, so exposure to the outside of the body is not a major concern. Inside the body, however, they can be very harmful. If alpha-emitters are inhaled, swallowed, or get into the body through a cut, the alpha particles can damage sensitive living tissue. The way these large, heavy particles cause damage makes them more dangerous than other types of radiation. The ionizations they cause are very close together - they can release all their energy in a few cells. This results in more severe damage to cells and DNA.

Beta Particles

Beta particles (β) are small, fast-moving particles with a negative electrical charge that are emitted from an atom’s nucleus during radioactive decay. These particles are emitted by certain unstable atoms such as hydrogen-3 (tritium), carbon-14 and strontium-90.

Beta particles are more penetrating than alpha particles, but are less damaging to living tissue and DNA because the ionizations they produce are more widely spaced. They travel farther in air than alpha particles, but can be stopped by a layer of clothing or by a thin layer of a substance such as aluminum. Some beta particles are capable of penetrating the skin and causing damage such as skin burns. However, as with alpha-emitters, beta-emitters are most hazardous when they are inhaled or swallowed.

Gamma Rays

Gamma rays (γ) are weightless packets of energy called photons. Unlike alpha and beta particles, which have both energy and mass, gamma rays are pure energy. Gamma rays are similar to visible light, but have much higher energy. Gamma rays are often emitted along with alpha or beta particles during radioactive decay.

Gamma rays are a radiation hazard for the entire body. They can easily penetrate barriers that can stop alpha and beta particles, such as skin and clothing. Gamma rays have so much penetrating power that several inches of a dense material like lead, or even a few feet of concrete may be required to stop them. Gamma rays can pass completely through the human body; as they pass through, they can cause ionizations that damage tissue and DNA.

X-Rays

Because of their use in medicine, almost everyone has heard of x-rays. X-rays are similar to gamma rays in that they are photons of pure energy. X-rays and gamma rays have the same basic properties but come from different parts of the atom. X-rays are emitted from processes outside the nucleus, but gamma rays originate inside the nucleus. They also are generally lower in energy and, therefore less penetrating than gamma rays. X-rays can be produced naturally or by machines using electricity.

Literally thousands of x-ray machines are used daily in medicine. Computerized tomography, commonly known as a CT or CAT scan, uses special x-ray equipment to make detailed images of bones and soft tissue in the body. Medical x-rays are the single largest source of man-made radiation exposure. Learn more about radiation sources and doses.  X-rays are also used in industry for inspections and process controls.

Periodic Table

Elements in the periodic table can take on several forms. Some of these forms are stable; other forms are unstable. Typically, the most stable form of an element is the most common in nature. However, all elements have an unstable form. Unstable forms emit ionizing radiation and are radioactive. There are some elements with no stable form that are always radioactive, such as uranium. Elements that emit ionizing radiation are called radionuclides.

What are isotopes?

The isotopes of an element are all the atoms that have in their nucleus the number of protons (atomic number) corresponding to the chemical behavior of that element. However, the isotopes of a single element vary in the number of neutrons in their nuclei. Since they still have the same number of protons, all these isotopes of an element have identical chemical behavior. But since they have different numbers of neutrons, these isotopes of the same element may have different radioactivity. An isotope that is radioactive is called a radioisotope or radionuclide. Two examples may help clarify this.

The most stable isotope of uranium, U-238, has an atomic number of 92 (protons) and an atomic weight of 238 (92 protons plus 146 neutrons). The isotope of uranium of greatest importance in atomic bombs, U-235, though, has three fewer neutrons. Thus, it also has an atomic number of 92 (since the number of protons has not changed) but an atomic weight of 235 (92 protons plus only 143 neutrons). The chemical behavior of U-235 is identical to all other forms of uranium, but its nucleus is less stable, giving it higher radioactivity and greater susceptibility to the chain reactions that power both atomic bombs and nuclear fission reactors.

Another example is iodine, an element essential for health; insufficient iodine in one's diet can lead to a goiter. Iodine also is one of the earliest elements whose radioisotopes were used in what is now called nuclear medicine. The most common, stable form of iodine has an atomic number of 53 (protons) and an atomic weight of 127 (53 protons plus 74 neutrons). Because its nucleus has the "correct" number of neutrons, it is stable and is not radioactive. A less stable form of iodine also has 53 protons (this is what makes it behave chemically as iodine) but four extra neutrons, for a total atomic weight of 131 (53 protons and 78 neutrons). With "too many" neutrons in its nucleus, it is unstable and radioactive, with a half-life of eight days. Because it behaves chemically as iodine, it travels throughout the body and localizes in the thyroid gland just like the stable form of iodine. But, because it is radioactive, its presence can be detected. Iodine 131 thus became one of the earliest radioactive tracers.

How can different isotopes of an element be produced?

How can isotopes be produced--especially radioisotopes, which can serve many useful purposes? There are two basic methods: separation and synthesis.

Some isotopes occur in nature. If radioactive, these usually are radioisotopes with very long half-lives. Uranium 235, for example, makes up about 0.7 percent of the naturally occurring uranium on the earth. The challenge is to separate this very small amount from the much larger bulk of other forms of uranium. The difficulty is that all these forms of uranium, because they all have the same number of electrons, will have identical chemical behavior: they will bind in identical fashion to other atoms. Chemical separation, developing a chemical reaction that will bind only uranium atoms, will separate out uranium atoms, but not distinguish among different isotopes of uranium. The only difference among the uranium isotopes is their atomic weight. A method had to be developed that would sort atoms according to weight.

One initial proposal was to use a centrifuge. The basic idea is simple: spin the uranium atoms as if they were on a very fast merry-go-round. The heavier ones will drift toward the outside faster and can be drawn off. In practice the technique was an enormous challenge: the goal was to draw off that very small portion of uranium atoms that were lighter than their brethren. The difficulties were so enormous the plan was abandoned in 1942. Instead, the technique of gaseous diffusion was developed. Again, the basic idea was very simple: the rate at which gas passed (diffused) througha filter depended on the weight of the gas molecules: lighter molecules diffused more quickly. Gas molecules that contained U-235 would diffuse slightly faster than gas molecules containing the more common but also heavier U-238. This method also presented formidable technical challenges, but was eventually implemented in the gigantic gas diffusion plant at Oak Ridge, Tennessee. In this process, the uranium was chemically combined with fluorine to form a hexafluoride gas prior to separation by diffusion. This is not a practical method for extracting radioisotopes for scientific and medical use. It was extremely expensive and could only supply naturally occurring isotopes.

A more efficient approach is to artificially manufacture radioisotopes. This can be done by firing high-speed particles into the nucleus of an atom. When struck, the nucleus may absorb the particle or become unstable and emit a particle. In either case, the number of particles in the nucleus would be altered, creating an isotope. One source of high-speed particles could be a cyclotron. A cyclotron accelerates particles around a circular race track with periodic pushes of an electric field. The particles gather speed with each push, just as a child swings higher with each push on a swing. When traveling fast enough, the particles are directed off the race track and into the target.

A cyclotron works only with charged particles, however. Another source of bullets are the neutrons already shooting about inside a nuclear reactor. The neutrons normally strike the nuclei of the fuel, making them unstable and causing the nuclei to split (fission) into two large fragments and two to three "free" neutrons. These free neutrons in turn make additional nuclei unstable, causing further fission. The result is a chain reaction. Too many neutrons can lead to an uncontrolled chain reaction, releasing too much heat and perhaps causing a "meltdown." Therefore, "surplus" neutrons are usually absorbed by "control rods." However, these surplus neutrons can also be absorbed by targets of carefully selected material placed in the reactor. In this way the surplus neutrons are used to create radioactive isotopes of the materials placed in the targets.

With practice, scientists using both cyclotrons and reactors have learned the proper mix of target atoms and shooting particles to "cook up" a wide variety of useful radioisotopes.

Radioactive decay is the process in which a radioactive atom spontaneously gives off radiation in the form of energy or particles to reach a more stable state.  It is important to distinguish between radioactive material and the radiation it gives off.

Types of Radiation

There are four types of radiation given off by radioactive atoms:

• Alpha particles
• Beta particles
• Gamma rays
• Neutrons

Radioactive atoms give off one or more of these types of radiation to reach a more stable state.  Additionally, each type of radiation has different properties that affect how we can detect it and how it can affect us.

Alpha Particles

• Alpha particles are large particles that travel up to an inch in the air. 
• Alpha particles are very easy to block, even with something as thin as a sheet of paper. 
• Alpha particles do not present an external hazard to people because they can’t get through our outer layer of dead skin cells. 
• However, they can be very damaging to cells inside our bodies if we breathe or eat alpha-emitting radioactive material or if the radioactive material is introduced through an open wound.

Beta Particles

• Beta particles are smaller particles that travel several feet in air. 
• Beta particles can be blocked effectively with a few inches of plastic, or even a layer of clothing.
• However, beta particles carry enough energy to cause burns on exposed skin and present an internal hazard if we breathe or eat beta-emitting radioactive material or if the radioactive material is introduced through an open wound.

Gamma Rays

• Gamma rays can travel many yards in air. 
• Gamma rays are primarily an external hazard because of their ability to go through material.
• It takes a few inches of lead or other dense substance to block gamma rays.
• Gamma rays also can be an internal hazard if we breathe or eat gamma-emitting radioactive materials, or if the radioactive material is introduce through an open wound, but the damage they do to cells inside our bodies is not as severe as that done by alpha and beta particles.
• The best way to protect yourself from a gamma-emitter is to increase the distance between yourself and the source.

Neutrons

Neutrons are neutral particles with no electrical charge that can travel great distances in the air.

• As neutrons travel through matter, they crash with atoms.  These atoms can become radioactive.
• Neutrons are more effective at damaging cells of the body than are other forms of ionizing radiation, such as x-rays or gamma rays.
• The best way to protect against neutron radiation is by providing shielding with thick, heavy materials such as lead, concrete, rock, or dirt.

Radionuclides can give off more than one kind of radiation, so it’s not uncommon to have a radionuclide that gives off both beta and gamma radiation, for example.

Half-Life

Another feature of each radionuclide is its half-life.  Half-life is the length of time it takes for half of the radioactive atoms of a specific radionuclide to decay.  A good rule of thumb is that, after seven half-lives, you will have less than one percent of the original amount of radiation.

Depending on the radionuclide, this process could be fast or take a very long time – radioactive half-lives can range from milliseconds to hours, days, sometimes millions of years. 

Radionuclides used in nuclear medicine procedures, have short half-lives. 

• For example, technetium-99m, one of the most common medical isotopes used for imaging studies, has a half-life of 6 hours. 
• The short half-life of technetium-99m helps keep the dose to the patient low. After 24 hours, the radioactivity from the procedure will be reduced by more than 90%.

Uranium is a radionuclide that has an extremely long half-life. 

• Naturally occurring uranium-238 present in the Earth’s crust has a half-life of almost 4.5 billion years. 
• If you take a soil sample anywhere in the world, including your backyard, you will find uranium atoms that date back to when the Earth was formed.

A Closer Look at Half-Life

Let’s take a closer look at half-life.

If you start with 100 atoms, after one half-life you’ll have 50 radioactive atoms.

After two half-lives, you’ll have 25 radioactive atoms.

And after a third half-life, you’ll have 12 radioactive atoms. 

Then 6, then 3, then 1, until eventually, all of the radioactive atoms in that population will reach their more stable state.

Radioactive Decay Chains

Some radionuclides go through a series of transformations before they reach a stable state.  For example, uranium-238 ultimately transforms into a stable atom of lead.  But in the process, several types of radioactive atoms are generated.  This is called a decay chain. When uranium-238 decays, it produces several isotopes of:

• Thorium
• Radium
• Radon
• Bismuth

Glossary

Alpha particles — The nucleus of a helium atom, made up of two neutrons and two protons with a charge of +2. Certain radioactive nuclei emit alpha particles. Alpha particles generally carry more energy than gamma or beta particles, and deposit that energy very quickly while passing through tissue. Alpha particles can be stopped by a thin layer of light material, such as a sheet of paper, and cannot penetrate the outer, dead layer of skin. Therefore, they do not damage living tissue when outside the body. When alpha-emitting atoms are inhaled or swallowed, however, they are especially damaging because they transfer relatively large amounts of ionizing energy to living cells. See also beta particle, gamma ray, neutron, x-ray.

Atom — The smallest particle of an element that can enter into a chemical reaction.

Beta Particles —  Electrons ejected from the nucleus of a decaying atom. Although they can be stopped by a thin sheet of aluminum, beta particles can penetrate the dead skin layer, potentially causing burns. They can pose a serious direct or external radiation threat and can be lethal depending on the amount received. They also pose a serious internal radiation threat if beta-emitting atoms are ingested or inhaled. See also alpha particle, gamma ray,neutron, x-ray.

Decay Chain (Decay Series) — The series of decays that certain radioisotopes go through before reaching a stable form. For example, the decay chain that begins with uranium-238 (U-238) ends in lead-206 (Pb-206), after forming isotopes, such as uranium-234 (U-234), thorium-230 (Th-230), radium-226 (Ra-226), and radon-222 (Rn-222).

Gamma Rays — High-energy electromagnetic radiation emitted by certain radionuclides when their nuclei transition from a higher to a lower energy state. These rays have high energy and a short wave length. All gamma rays emitted from a given isotope have the same energy, a characteristic that enables scientists to identify which gamma emitters are present in a sample. Gamma rays penetrate tissue farther than do beta or alpha particles, but leave a lower concentration of ions in their path to potentially cause cell damage. Gamma rays are very similar to x-rays. See also neutron.

Isotope — A nuclide of an element having the same number of protons but a different number of neutrons.

Neutron — A small atomic particle possessing no electrical charge typically found within an atom’s nucleus. Neutrons are, as the name implies, neutral in their charge. That is, they have neither a positive nor a negative charge. A neutron has about the same mass as a proton. See also alpha particle, beta particle, gamma ray, nucleon, x-ray.

Radioactive Decay — Disintegration of the nucleus of an unstable atom by the release of radiation.

Radiation — Energy moving in the form of particles or waves. Familiar radiations are heat, light, radio waves, and microwaves. Ionizing radiation is a very high-energy form of electromagnetic radiation.

Radioactive Material — Material that contains unstable (radioactive) atoms that give off radiation as they decay.

Radionuclide — An unstable and therefore radioactive form of a nuclide.

Half-life: 432.2 years

Mode of decay: Alpha particles and weak gamma radiation

Chemical properties: Crystalline metal that is solid under normal conditions. Am-241 can be combined with beryllium to produce neutrons.

What is it used for?

Am-241 is used in some medical diagnostic devices and in a variety of industrial and commercial devices that measure density and thickness. Tiny Am-241 sources are also present in smoke detectors.

Where does it come from?

Am-241 is a manmade metal that is produced from plutonium. Am-241 found in the environment is the result of past nuclear weapons testing.

What form is it in?

Am-241 found in the environment is in the form of microscopic dust. Am-241 used in industrial, medical, or commercial devices is in the form of coin-sized metal or plastic discs. The Am-241 source present in a smoke detector is inside a metal cylinder that is about the size of a pencil erasure.

What does it look like?

Am-241 is a silver-white metal that is solid under normal conditions.

How can it hurt me?

As a dust or fine powder, Am-241 can cause certain cancers. When Am-241 powder is swallowed, absorbed through a wound, or inhaled it can stay in the body for decades. Am-241 concentrates in the bones, liver, and muscles, exposing these organs to alpha particles.

Half-life: 30.17 years

Mode of decay: Beta and gamma radiation

Chemical properties: Liquid at room temperature, but readily bonds with chlorides to form a powder.

What is it used for?

Cs-137 is used in small amounts for calibration of radiation-detection equipment, such as Geiger-Mueller counters. In larger amounts, Cs-137 is used in medical radiation therapy devices for treating cancer; in industrial gauges that detect the flow of liquid through pipes; and in other industrial devices to measure the thickness of materials, such as paper, photographic film, or sheets of metal.

Where does it come from?

Cs-137 is produced by nuclear fission for use in medical devices and gauges. Cs-137 also is one of the byproducts of nuclear fission processes in nuclear reactors and nuclear weapons testing. Small quantities of Cs-137 can be found in the environment from nuclear weapons tests that occurred in the 1950s and 1960s and from nuclear reactor accidents, such as the Chernobyl power plant accident in 1986, which distributed Cs-137 to many countries in Europe.

What form is it in?

Because it readily bonds with chlorides, Cs-137 usually occurs as a crystalline powder, rather than in its pure liquid form.

What does it look like?

Small amounts of Cs-137 are incorporated into Lucite disks, rods, and seeds. Larger Cs-137 sources are enclosed in lead containers (such as long tubes that are closed at each end) or small round metal containers. If the lead containers of Cs-137 are opened, the substance inside looks like a white powder and may glow. Cs-137 from nuclear accidents or atomic bomb explosions cannot be seen and will be present in dust and debris from fallout.

How can I be exposed to Cs-137?

Small amounts of Cs-137 are present in the environment from weapons testing in the 1950s and 1960s, so people are exposed to some Cs-137 every day. However, Cs-137 is dangerous in the large, concentrated amounts found in radiation therapy units and industrial gauges. The sources in these devices are designed to remain sealed and keep people from being exposed; however, if these canisters are intentionally or accidentally opened, the Cs-137 inside could be dispersed.

How can it hurt me?

External exposure to large amounts of Cs-137 can cause burns, acute radiation sickness, and even death. Exposure to Cs-137 can increase the risk for cancer because of exposure to high-energy gamma radiation. Internal exposure to Cs-137, through ingestion or inhalation, allows the radioactive material to be distributed in the soft tissues, especially muscle tissue, exposing these tissues to the beta particles and gamma radiation and increasing cancer risk.

Half-life: 5.27 years

Mode of decay: Beta particles and gamma radiation

Chemical properties: Metallic solid that can become magnetically charged

What is it used for?

Co-60 is used medically for radiation therapy as implants and as an external source of radiation exposure. It is used industrially in leveling gauges and to x-ray welding seams and other structural elements to detect flaws. Co-60 also is used for food irradiation, a sterilization process.

Where does it come from?

Nonradioactive cobalt occurs naturally in various minerals and has long been used as a blue coloring agent for ceramic and glass. Radioactive Co-60 is produced commercially through linear acceleration for use in medicine and industry. Co-60 also is a byproduct of nuclear reactor operations, when metal structures, such as steel rods, are exposed to neutron radiation.

What form is it in?

Co-60 occurs as a solid material and might appear as small metal disks or in a tube, enclosed at both ends, that holds the small disks. Co-60 can occur as a powder if the solid sources have been ground or damaged.

What does it look like?

Co-60 is a hard, gray-blue metal. It resembles iron or nickel.

How can it hurt me?

Because it decays by gamma radiation, external exposure to large sources of Co-60 can cause skin burns, acute radiation sickness, or death. Most Co-60 that is ingested is excreted in the feces; however, a small amount is absorbed by the liver, kidneys, and bones. Co-60 absorbed by the liver, kidneys, or bone tissue can cause cancer because of exposure to the gamma radiation.

Half-life: 8.06 days

Mode of decay: Beta particles and gamma radiation

Chemical properties: I-131 can change directly from a solid into a gas, skipping the liquid phase, in a process called sublimation. I-131 dissolves easily in water or alcohol. I-131 readily combines with other elements and does not stay in its pure form once released into the environment.

What is it used for?

I-131 is used in medicine to diagnose and treat cancers of the thyroid gland.

Where does it come from?

I-131 is produced commercially for medical and industrial uses through nuclear fission. It also is a byproduct of nuclear fission processes in nuclear reactors and weapons testing.

What form is it in?

In medicine, I-131 is supplied in capsules or liquid of a specific activity designed to be swallowed by patients. As a product of nuclear fission, it is a dark purple gas that can be inhaled, or absorbed through the skin. I-131 in fallout from nuclear weapons or reactor accidents can occur in particle form, which can be ingested in food or water.

What does it look like?

Pure I-131 is a non-metallic, purplish-black crystalline solid. However, because it readily binds with other elements, I-131 usually is found as a compound rather than in its pure form. For medical purposes, the I-131 capsules contain small granules of I-131 sodium iodide that are designed to be swallowed by patients. Liquid I-131 sodium iodide used to diagnose and treat thyroid disease is a clear liquid.

How can it hurt me?

External exposure to large amounts of I-131 can cause burns to the eyes and on the skin. Internal exposure can affect the thyroid gland, a small organ located in the neck near the Adam’s apple. The thyroid gland uses iodine to produce thyroid hormones and cannot distinguish between radioactive iodine and stable (nonradioactive) iodine. If I-131 were released into the atmosphere, people could ingest it in food products or water, or breathe it in. In addition, if dairy animals consume grass contaminated with I-131, the radioactive iodine will be incorporated into their milk. Consequently, people can receive internal exposure from drinking the milk or eating dairy products made from contaminated milk. Once inside the body, I-131 will be absorbed by the thyroid gland exposing it to radiation and potentially increasing the risk for thyroid cancer or other thyroid problems.

Half-life: 73.83 days

Mode of decay: Beta particles and gamma radiation.

Chemical Properties: Dense metal. Metallic Ir-192 will react with fluorine gas to form iridium fluoride (IV), IrF 6.

What is it used for?

Ir-192 is used in industrial gauges that inspect welding seams and in medicine to treat certain cancers.

Where does it come from?

Ir-192 is a manmade radioactive element that is formed from nonradioactive iridium metal in a nuclear reactor.

What form is it in?

Ir-192 used in medicine is in the form of tiny seeds, each about the size of a grain of rice. Industrial gauges hold pencil-like metal sticks of solid Ir-192 or small pencil-like tubes that contain pellets of Ir-192.

What does it look like?

Ir-192 is a shiny, silvery-white, very dense metal that will not rust when exposed to natural elements.

How can it hurt me?

Exposure to Ir-192 can increase the risk for cancer because of its high-energy gamma radiation. External exposure to Ir-192 can cause burns, acute radiation sickness, and even death. Internal exposure could occur only if a person were to swallow one of the Ir-192 seeds or pellets. Internal exposure from Ir-192 could cause burns in the stomach and intestines if the high-energy industrial pellets are swallowed. Ir-192 seeds and pellets would be excreted in the feces. Long-term health effects of internal exposure would depend on how strong the seeds or pellets were and how long they stayed in the body.

Plutonium-238 (Pu-238)
Half-life: 87.7 years

Plutonium-239 (Pu-239)
Half-life: 24,110 years

Plutonium-240 (Pu-240)
Half-life: 6,564 years

Mode of decay: Alpha particles

Chemical properties: Solid under normal conditions, plutonium can form compounds with other elements.

What is it used for?

Plutonium-238 generates significant heat through its radioactive decay process, which makes it useful as a heat source for sensitive electrical components in satellites, as a well as a power source (for example, battery power) for satellites. Plutonium-239 is used to make nuclear weapons. Pu-239 and Pu-240 are byproducts of nuclear reactor operations and nuclear bomb explosions.

Where does it come from?

Plutonium is created from uranium in nuclear reactors. It is a by-product of nuclear weapons production and nuclear power operations.

What form is it in?

Plutonium is a solid material that is fashioned into rods for use in nuclear reactors and into ceramic ?buttons? for use in satellite systems.

What does it look like?

Plutonium is a silvery-gray metal that becomes yellowish when exposed to air. Most plutonium in the environment is in the form of microscopic particles that are the remnants of nuclear weapons testing and nuclear reactor accidents.

How can it hurt me?

Because it emits alpha particles, plutonium is most dangerous when inhaled. When plutonium particles are inhaled, they lodge in the lung tissue. The alpha particles can kill lung cells, which causes scarring of the lungs, leading to further lung disease and cancer. Plutonium can enter the blood stream from the lungs and travel to the kidneys, meaning that the blood and the kidneys will be exposed to alpha particles. Once plutonium circulates through the body, it concentrates in the bones, liver, and spleen, exposing these organs to alpha particles. Plutonium that is ingested from contaminated food or water does not pose a serious threat to humans because the stomach does not absorb plutonium easily and so it passes out of the body in the feces.

Half-life: 29.1 years

Mode of decay: Beta radiation

Chemical properties: Chemically reactive; can create halide, oxide, and sulfide compounds

What is it used for?

Because Sr-90 generates heat as it decays, it is used as a power source for space vehicles, remote weather stations, and navigational beacons. It also is used in industrial gauges and medically, in a controlled manner, to treat bone tumors.

Where does it come from?

Sr-90 is produced commercially through nuclear fission for use in medicine and industry. It also is found in the environment from nuclear testing that occurred in the 1950s and 1960s and in nuclear reactor waste and can contaminate reactor parts and fluids.

What form is it in?

Sr-90 is a soft metal. It can be present in dust from nuclear fission after detonation of nuclear weapons or a nuclear power plant accident.

What does it look like?

In its pure form, Sr-90 is a soft, shiny silver metal, but it quickly changes to yellow when exposed to air.

How can it hurt me?

Sr-90 can be inhaled, but ingestion in food and water is the greatest health concern. Once in the body, Sr-90 acts like calcium and is readily incorporated into bones and teeth, where it can cause cancers of the bone, bone marrow, and soft tissues around the bone.

Sr-90 decays to yttrium 90 (Y-90), which in turn decays by beta radiation so that wherever Sr-90 is present Y-90 is also present. Because of the beta radiation, Y-90 poses a risk of burns to the eyes and on the skin from external exposure.

Technetium (chemical symbol Tc) is a silver-gray, radioactive metal. It occurs naturally in very small amounts in the earth's crust, but is primarily man-made. Technetium-99 is produced during nuclear reactor operation, and is a byproduct of nuclear weapons explosions. Technetium-99 can be found as a component of nuclear waste.

Technetium-99m is a short-lived form of Tc-99 that is used as a medical diagnostic tool. It has a short half-life (6 hours) and does not remain in the body or the environment for long.

Type of Radiation Emitted:
Beta Particles

Half-life:
Technetium-99: 210,000 years
Technetium-99m: 6 hours

Technetium in the Environment

Air, sea water, soils, plants and animals contain very low concentrations of Tc-99. Because of its long half-life, Tc-99 remains in the environment for an extended period of time.

Organic matter in soils and sediments slow the transport of Tc-99. In the presence of oxygen, plants readily take up technetium compounds from the soils. Some plants such as brown algae in seawater are able to concentrate Tc-99. Sea animals can also concentrate Technetium-99 in their bodies.

Technetium Sources

Tiny amounts of Tc-99 are part of the environment and are found in food and water. Higher amounts may be found close to contaminated facilities such as federal weapons facilities or nuclear fuel cycle facilities.

Exposure to technetium from the environment is unlikely. Most human exposure to technetium comes from the intentional use of Tc-99m in nuclear medicine.

Technetium and Health

Technetium-99 can pose a health risk when it enters the body. Once in the human body, Tc-99 concentrates in the thyroid gland and the gastrointestinal tract. However, the body constantly gets rid of Tc-99 in feces. As with any other radioactive material, there is an increased chance that cancer or other adverse health effects can result from exposure to  radiation .

The Tc-99m used in medical diagnostics has a short, six-hour half-life and does not remain in the body.

Thorium (chemical symbol Th) is a naturally occurring radioactive metal found at trace levels in soil, rocks, water, plants and animals. Thorium is solid under normal conditions. There are natural and man-made forms of thorium, all of which are radioactive. In general, naturally occurring thorium exists as Th-232, Th-230 or Th-228.

Type of Radiation Emitted:
Alpha Particles
weak Gamma Rays

Half-life:
Thorium-232: 14 billion years
Thorium-230: 77,000 years
Thorium-228: 1.9 years

Thorium in the Environment

Natural thorium is present in trace quantities in virtually all rock, soil, water, plants and animals. Where higher concentrations occur in rock or sands, thorium may be mined and refined, producing waste products such as mill tailings. If not properly controlled, wind and water can introduce the tailings into the wider environment. Commercial and federal facilities that have processed thorium may also have released thorium to the air, water or soil. Man-made thorium  isotopes  are rare, and almost never enter the environment.

Thorium Sources

Thorium is used to make ceramics, welding rods, camera and telescope lenses, fire brick, heat resistant paint and metals used in the aerospace industry, as well as in nuclear reactions. Thorium has the potential to be used as a fuel for generating nuclear energy.

Since thorium is naturally present in the environment, people are exposed to tiny amounts in air, food and water. The amounts are usually very small and pose little health hazard.

Most people are not exposed to dangerous levels of thorium. However, people who live near thorium mining areas or near certain legacy industrial facilities may have increased exposure to thorium.

Occasionally, household items may be found with thorium in them, such as some older ceramic wares in which uranium and thorium were used in the glaze. These generally do not pose serious health risks, but may nevertheless be retired from use as a prudent avoidance measure.

Thorium and Health

If inhaled as dust, some thorium may remain in the lungs for long periods of time, depending on the chemical form. If ingested, thorium typically leaves the body through feces and urine within several days. The small amount of thorium left in the body will enter the bloodstream and be deposited in the bones where it may remain for many years.

Inhaling thorium dust may cause an increased risk of developing lung or bone cancer.

Uranium-235 (U-235)
Half-life: 700 million years

Uranium-238 (U-238)
Half-life: 4.47 billion years

Mode of decay: Alpha particles

Chemical properties: Weakly radioactive, extremely dense metal (65% denser than lead)

What is it used for?

Uranium “enriched” into U-235 concentrations can be used as fuel for nuclear power plants and the nuclear reactors that run naval ships and submarines. It also can be used in nuclear weapons.

Depleted uranium (uranium containing mostly U-238) can be used for radiation shielding or as projectiles in armor-piercing weapons.

Where does it come from?

U-235 and U-238 occur naturally in nearly all rock, soil, and water. U-238 is the most abundant form in the environment. U-235 can be concentrated in a process called “enrichment,” making it suitable for use in nuclear reactors or weapons.

What form is it in?

Uranium is an extremely heavy metal. Enriched uranium can be in the form of small pellets that are packaged in the long tubes used in nuclear reactors.

What does it look like?

When it has been refined and enriched, uranium is a silvery-white metal.

How can it hurt me?

Because uranium decays by alpha particles, external exposure to uranium is not as dangerous as exposure to other radioactive elements because the skin will block the alpha particles. Ingestion of high concentrations of uranium, however, can cause severe health effects, such as cancer of the bone or liver. Inhaling large concentrations of uranium can cause lung cancer from the exposure to alpha particles. Uranium is also a toxic chemical, meaning that ingestion of uranium can cause kidney damage from its chemical properties much sooner than its radioactive properties would cause cancers of the bone or liver.