Key points

• Electromagnetic radiation is energy that comes from a source and travels through space at the speed of light.
• Electromagnetic radiation has an electric field and a magnetic field associated with it and has wave-like properties.
• You could also call electromagnetic radiation “electromagnetic waves."

What it is

Radiation with the highest energy includes forms like far ultraviolet radiation, x-rays, and gamma rays. X-rays and gamma rays have a lot of energy. When they interact with atoms, they can remove electrons and cause the atom to become ionized.

Categories

The radioactive atom

• Radioactive atoms have unstable blends of protons and neutrons.
• Radioactivity is the spontaneous release of energy from an unstable atom to get to a more stable state.
• Ionizing radiation is the energy that comes out of a radioactive atom.
• Radioactive isotopes are radioactive atoms of the same element that have different numbers of neutrons

Properties of radioactive isotopes

• Radioactive atoms can give off four types of ionizing radiation: alpha particles, beta particles, gamma rays, and neutrons.
• Each type of radiation has different properties. Their properties affect how we can detect it and how it can affect us.
• An unstable atom changes into a more stable atom of the same or different element by giving off radiation. This process is called radioactive decay.
• A half-life is the length of time it takes for half of the radioactive atoms in a group of radioactive isotopes to decay.

Preventing exposure

The guiding principle of radiation safety is "ALARA." ALARA stands for "as low as reasonably achievable."

ALARA means avoiding exposure to radiation that does not have a direct benefit to you, even if the dose is small. To do this, you can use three basic protective measures in radiation safety: time, distance, and shielding.

Key points

• There is a wide range of electromagnetic radiation in nature, and visible light is one example.
• Radiation with the highest energy includes forms like ultraviolet radiation, x-rays, and gamma rays.
• X-rays and gamma rays can remove electrons and cause the atom to become ionized.

Overview

The most common form of radiation we are all familiar with is visible light. Light is energy that originates from a source and travels through space at the speed of...light! It has a particular frequency that defines its energy.

We can detect this visible radiation with our eyes. The only difference between various colors of light is in their wavelength and frequency or in other words in their energy. Red light, for example, has less energy than purple light.

The visible part of the spectrum is only a tiny part of this wide range of energies.

As we move lower in frequency from red light, there are other familiar forms of electromagnetic radiation:

• Infrared
• Microwaves
• Signals from our cell phones
• Radio waves

These are all forms of radiation that are invisible to our eyes and that have less energy than visible light or light of different colors.

As we move up (higher) in frequency from purple light, there are:

• Ultraviolet (UV) radiation
• X-rays
• Gamma rays

These are all forms of radiation with energies much higher than visible light.

X-rays and gamma rays have enough energy that during interaction with atoms, they can remove electrons. This causes the atom to become charged or ionized. That's why we refer to this as ionizing radiation. When most people talk about radiation, they are referring to ionizing radiation.

Ionization is a unique property that other forms of radiation at lower frequencies do not have.

Key points

• Ionizing radiation is a powerful form of energy with medical applications such as diagnostic testing.
• At high enough doses, it can alter your body's cells and DNA.
• Unlike some non-ionizing radiation, it can cause serious harm or cancer with enough exposure.

Overview

Radiation exists all around us and is in two forms: ionizing and non-ionizing radiation.

Non-ionizing radiation is a form of radiation with less energy than ionizing radiation. Non-ionizing radiation does not remove electrons from atoms or molecules of materials that include air, water, and living tissue.

Ionizing radiation explained

One form of ionizing radiation is electromagnetic waves. Some electromagnetic waves have enough energy and can remove electrons from atoms and molecules of materials. These materials include air, water, and living tissue. Electromagnetic wave radiation can travel unseen and pass through these materials. High energy, ionizing, electromagnetic waves are shown on the right side of the electromagnetic spectrum in the figure below.

A familiar example of ionizing radiation is that of x-rays, which can penetrate our body and reveal pictures of our bones. We say that x-rays are "ionizing," meaning that they have the unique capability to remove electrons from atoms and molecules.

Electrons are taken from the matter through which they pass. Ionizing activity can alter molecules within the cells of our body. That action may cause eventual harm (such as cancer). Intense exposures to ionizing radiation may produce visible skin or tissue damage.

Types

We are exposed to low levels of ionizing radiation every day.

Sources of ionizing radiation fall into two categories: natural and manmade.

Ionizing radiation from natural sources

Ionizing radiation that comes from natural sources is typically at low levels. This means that the usual amount of ionizing radiation from natural sources absorbed by our bodies (dose) is small.

In nature, sources of ionizing radiation include:

• Radiation from space (cosmic and solar radiation)
• Radiation from the earth (terrestrial radiation)
• Radon
• Radiation from building materials

Ionizing radiation from manmade sources

Every day, we use Ionizing radiation to help us live healthy lives. For example, ionizing radiation is found in smoke detectors and used to disinfect medical instruments and blood. It is also a byproduct of nuclear power generation.

Our main exposure to ionizing radiation in manmade sources is through the use of diagnostic medical exams.

Medical exams that use ionizing radiation include:

• X-rays
• CT or CAT (computed tomography) scans
• PET (positron emission tomography) scans
• Fluoroscopy
• Nuclear medicine procedures

Risk of exposure to ionizing radiation

Ionizing radiation can penetrate the human body and the radiation energy can be absorbed in tissue. This has the potential to cause harmful effects to people, especially at high levels of exposure.

Natural sources

Natural sources of ionizing radiation usually release ionizing radiation at low levels. This means the amounts of radiation absorbed by our bodies (doses) is usually small. Natural sources of ionizing radiation include radioactive elements that are naturally in our body. For example, a very small fraction of the potassium in our bodies is radioactive.

Radon, however, is a natural radioactive gas found in rock formations. Radon can release higher levels of radiation that can pose health risks. It is the second leading cause of lung cancer in the United States. The levels of radon in your home or building depend on a variety of factors. You can test your home or building to determine whether you are at risk of high levels of radon exposure.

Manmade sources

Medical diagnostic exams are the main manmade source of ionizing radiation exposure in the United States. The goal of medical diagnostic imaging is for the benefits to far outweigh the risks.

You can track the number and type of these medical diagnostic exams that you receive on a regular basis. By tracking your diagnostic exams, you can share your history with your medical provider.

Consult with your health care professional on how an exam will help. There may be another test that does not contain ionizing radiation may provide the same benefit. Magnetic Resonance Imaging (MRIs) and ultrasound technology are examples of diagnostic exams that do not involve exposure to ionizing radiation.

Key points

• Ionized atoms can occur naturally in the environment and are considered unstable.
• Atoms seek to be stable and may release energy to become stable.
• The energy released from the atom is known as radiation.

Overview

Ionizing radiation comes from radioactive atoms, many of which occur naturally in the environment. Radioactive atoms, just like any other form of matter, can be in gas, liquid, or solid forms.

Atoms are the building blocks of matter. Their structure determines their elemental and chemical properties. They are composed of a nucleus, containing protons and neutrons, surrounded by a cloud of electrons.

The number of protons in the nucleus determines the identity of the atom (chemical element). For example, a carbon atom has six protons. If you were able to add another proton to the carbon nucleus, you wouldn't have a carbon atom anymore. You would have a nitrogen atom instead. Atoms with the same number of protons but different numbers of neutrons are called isotopes.

Most atoms are stable, meaning they have a good balance of neutrons and protons. But some atoms have an unstable combination blend of protons and neutrons, and these are considered radioactive. To get to a more stable state, the atom expels energy from the nucleus in the form of a particle or ray. This process is known as radioactivity and the energy that's released is radiation.

After an atom expels energy from the nucleus, the composition of the nucleus changes, and we are left with a different element that is more stable. This process is known as radioactive decay.

Terms to know

• Radioactivity is the spontaneous release of energy from an unstable atom.
• Radioactive material is a solid, liquid, or gas that gives off radiation.
• Radiation is the energy that comes out of a radioactive atom.
• Radioactive isotopes, also known as radionuclides, are radioactive atoms of the same element that have different numbers of neutrons.
• Radioactive decay is the change from an unstable atom to a more stable atom by the emission of radiation.

Different radioactive isotopes give off different kinds of radiation, and decay at different rates.

Radioactive Decay Example

Think of the carbon atom mentioned above. Every carbon atom has six protons, and the majority of carbon atoms have six neutrons.

But some types of carbon have more than six neutrons. Isotopes are forms of elements that have a different number of neutrons. For example, carbon-14 is a radioactive isotope of carbon that has six protons and eight neutrons in its nucleus. We call it carbon-14 because the total number of protons and neutrons in the nucleus adds up to 14.

If we wanted to abbreviate the name of an isotope, we'd use the elemental symbol and the mass number. For example, carbon-14 would be abbreviated C-14.

Because carbon-14 has six protons, it is still carbon, but the two extra neutrons make the nucleus unstable. In order to reach a more stable state, carbon-14 releases a negatively charged particle from its nucleus. That action turns one of the neutrons into a proton.

In the carbon-14 example, the atom gives off radiation from the nucleus to reach a more stable state. In doing so, the composition of the nucleus changes, and we are left with a different element that is more stable but may still be radioactive. This process is known as radioactive decay.

Resources

Glossary

Atom — The smallest amount of an element that still has the properties of the element.

Electron — An elementary particle with a negative electrical charge and a mass 1/1837 that of the proton. Electrons surround the nucleus of an atom because of the attraction between their negative charge and the positive charge of the nucleus. A stable atom will have as many electrons as it has protons. The number of electrons that orbit an atom determine its chemical properties.

Ionizing radiation — Any radiation capable of displacing electrons from atoms, thereby producing ions. High doses of ionizing radiation may produce severe skin or tissue damage.

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.

Nucleus — The central part of an atom that contains protons and neutrons. The nucleus is the heaviest part of the atom.

Proton — A small atomic particle, typically found within an atom's nucleus, that possesses a positive electrical charge. Even though protons and neutrons are about 2,000 times heavier than electrons, they are tiny. The number of protons is unique for each chemical element.

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

Key points

• Radioactive decay occurs when a radioactive atom gives off radiation in the form of energy or particles.
• Radioactive atoms give off radiation to become more stable.
• There are four types of radiation given off by radioactive atoms.

Overview

Radioactive decay is the process in which a radioactive atom spontaneously gives off radiation. This radiation is given off 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.

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
• Lead

Types

There are four types of radiation given off by radioactive atoms. 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 very easy to block, even with something as thin as a sheet of paper. They 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. Damage can also occur if the radioactive material is introduced through an open wound.

Beta particle

Beta particles can be blocked effectively with a few inches of plastic, or even a layer of clothing. However, beta particles can carry enough energy to cause burns on exposed skin. They can present an internal hazard if we breathe or eat beta-emitting radioactive material. Radioactive material may also be introduced through an open wound.

Gamma rays

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 can be an internal hazard if we breathe or eat gamma-emitting radioactive materials.

Radioactive material can also be introduced through an open wound. 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 can travel great distances in the air. As neutrons travel through matter, they crash into 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. The best way to protect against neutron radiation is by providing shielding. Good shielding materials against neutrons include thick materials such as, concrete, rock, or dirt. The best shielding against neutrons contains a lot of water or hydrogen.

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. 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 less than a nanosecond, to hours, days, or sometimes millions and billions of years or more.

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.

And after a third half-life, you'll have 12 radioactive atoms. Then 6, then 3, then 1. Eventually, all of the radioactive atoms in that population will reach their more stable state.

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. They 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. Alpha particles 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. This allows them to transfer relatively large amounts of ionizing energy to living cells.

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. 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.

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). This transformation forms 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 wavelength. Gamma rays emitted from a given isotope can have many different energies.

This characteristic enables scientists to identify which gamma emitters are present in a sample. Gamma rays penetrate tissue farther than do beta or alpha particles. However, they leave a lower concentration of ions in their path to potentially cause cell damage. Gamma rays have a shorter wavelength, higher frequency, and higher energy than x-rays.

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.

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 can be very high-energy electromagnetic radiation like gamma rays, lower energy x-rays, charged particles such as alpha or beta particles, and neutrons.

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.

Key points

• Non-ionizing radiation exists all around us from many sources.
• Unlike ionizing radiation, non-ionizing radiation does not have enough energy to remove electrons.
• You are exposed to low levels of non-ionizing radiation every day, but intense exposure may result in damage to tissue.

Overview

Radiation exists all around us, from both natural and manmade sources, and is in two forms: ionizing and non-ionizing radiation.

Ionizing radiation is a form of energy that acts by removing electrons from atoms and molecules of materials. These materials include air, water, and living tissue. Ionizing radiation can travel unseen and pass through these materials.

Non-ionizing radiation explained

Non-ionizing radiation is to the left of ionizing radiation on the electromagnetic spectrum in the figure below.

The dividing line between ionizing and non-ionizing radiation occurs in the ultraviolet part of the electromagnetic spectrum. Radiation in the ultraviolet band and at lower energies (to the left of ultraviolet) is called non-ionizing radiation. Radiation to the right of the ultraviolet band and at higher energies is called ionizing radiation.

Ionizing vs non-ionizing radiation

Non-ionizing radiation differs from ionizing radiation in the way it acts on materials like air, water, and living tissue.

Unlike x-rays and other forms of ionizing radiation, non-ionizing radiation does not have enough energy to remove electrons. Non-ionizing radiation can heat substances. For example, the microwave radiation inside a microwave oven heats water and food rapidly.

Exposure

You are exposed to low levels of non-ionizing radiation every day. Exposure to highly intense, direct amounts of non-ionizing radiation may result in damage to tissue due to heat. This is not common and mainly of concern in the workplace for those who work on large sources of non-ionizing radiation.

Risk from ultraviolet radiation exposure

Ultraviolet radiation is a natural part of solar radiation, and also is released by black lights, tanning beds, and electric arc lighting. UV light reaching the earth's surface is non-ionizing. Normal everyday levels of UV radiation can be helpful, and produce vitamin D. The World Health Organization (WHO) recommends 5 to 15 minutes of sun exposure 2 to 3 times a week.

Too much UV radiation can cause skin burns, premature aging of the skin, eye damage, and skin cancer. The majority of skin cancers are caused by exposure to ultraviolet radiation.

Tanning through the use of tanning beds and tanning devices exposes the consumer to UV radiation. Exposure to tanning beds and tanning devices also increases the chance of developing skin cancer.

Risk from exposure to radiofrequency and microwave radiation

Intense, direct exposure to radiofrequency and microwave radiation may result in damage to tissue due to heat. These more significant exposures could occur from industrial devices in the workplace.

Key points

• People can become contaminated with radioactive materials when the materials get on their clothes, hair, or skin.
• People can also become contaminated if radioactive materials enter their body through swallowing, breathing, or open wounds.
• People can spread contamination to others and should take steps to decontaminate themselves.

What causes it

Radioactive contamination and radiation exposure could occur as the result of an accident, an event in nature, or an act of terrorism. Such a release could expose people and contaminate their surroundings and personal property.

Radiation exposure

Radioactive materials give off a form of energy that travels in waves or particles. This energy is called radiation.

When a person is exposed to radiation, the energy enters the body. For example, when a person has an X-ray, he or she is exposed to radiation.

Radioactive contamination

Radioactive contamination occurs when radioactive material is deposited on or in an object or a person. A contaminated person has radioactive materials on or inside their body. Radioactive materials released into the environment can cause contamination of:

• Air
• Water
• Surfaces
• Plants and soil
• Buildings
• People
• Animals

External contamination

External contamination occurs when radioactive material, in the form of dust, powder, or liquid, comes into contact with:

• Skin
• Hair
• Clothing

In other words, the contact with radioactive material is outside your body. If you are externally contaminated, you can become internally contaminated if radioactive material gets into your body.

Internal contamination

Internal contamination occurs when you swallow or breathe in radioactive materials. It also happens when radioactive materials enter the body through an open wound or are absorbed through the skin.

Some types of radioactive materials stay in the body and accumulate in different body organs. Other types are eliminated from the body in:

• Blood
• Sweat
• Urine
• Feces

How contamination spreads

If you are externally contaminated with radioactive material, you can contaminate other people or surfaces that you touch. For example, if you have radioactive dust on your clothing, you may spread the radioactive dust when you sit in chairs or hug other people.

If you are internally contaminated, you can expose people near you to radiation from the radioactive material inside your body. Body fluids (blood, sweat, urine) can contain radioactive materials if you are contaminated. Touching these body fluids can result in contamination or exposure.

Contamination at home

If you are externally contaminated, you can spread the contamination by

• Touching surfaces
• Sitting in a chair
• Walking through a house

Contaminants can easily fall from clothing and contaminate other surfaces.

Homes can also become contaminated with radioactive materials from body fluids of people with internal contamination.

Making sure that others do not come in contact with dust or body fluids from a person with contamination will help prevent contamination of other people in the home.

Prevention methods

Because radiation cannot be seen, smelled, felt, or tasted, people at the site of an incident will not know whether radioactive materials were involved. You can take the following steps to limit your contamination:

1. Get out of the current area quickly. Go inside to the closest safe building or to an area to which you are directed by law enforcement or health officials.
2. Remove the outer layer of your clothing. If radioactive material is on your clothes, getting it away from you will reduce the external contamination and decrease the risk of internal contamination. It will also reduce the length of time that you are exposed to radiation.
3. If possible, place the clothing in a plastic bag or leave it in an out-of-the-way area, such as the corner of a room. Keep people away from it to reduce their exposure to radiation. Keep cuts and abrasions covered when handling contaminated items to avoid getting radioactive material in them.
4. Wash all of the exposed parts of your body using lots of soap and lukewarm water to remove contamination. This process is called decontamination. Try to avoid spreading contamination to parts of the body that may not be contaminated, such as areas that were clothed.
5. After authorities determine that internal contamination may have occurred, you may be able to take medication to reduce the radioactive material in your body. There are some medications that can help remove internal contamination from certain radioactive materials.

Sources of radiation are all around us all the time. Some are natural and some are man-made. The amount of radiation absorbed by a person is measured in dose. A dose is the amount of radiation energy absorbed by the body.

Background Radiation

Background radiation is present on Earth at all times. The majority of background radiation occurs naturally from minerals and a small fraction comes from man-made elements. Naturally occurring radioactive minerals in the ground, soil, and water produce background radiation. The human body even contains some of these naturally-occurring radioactive minerals. Cosmic radiation from space also contributes to the background radiation around us. There can be large variances in natural background radiation levels from place to place, as well as changes in the same location over time.

Cosmic Radiation

Cosmic radiation comes from extremely energetic particles from the sun and stars that enter Earth’s atmosphere. Some particles make it to the ground, while others interact with the atmosphere to create different types of radiation. Radiation levels increase as you get closer to the source, so the amount of cosmic radiation generally increases with elevation. The higher the altitude, the higher the dose. That is why those living in Denver, Colorado (altitude of 5,280 feet) receive a higher annual radiation dose from cosmic radiation than someone living at sea level (altitude of 0 feet).

Radioactive Materials in the Earth and in Our Bodies

Uranium and thorium naturally found in the earth are called primordial radionuclides and are the source of terrestrial radiation. Trace amounts of uranium, thorium and their decay products can be found everywhere. Terrestrial radiation levels vary by location, but areas with higher concentrations of uranium and thorium in surface soils generally have higher dose levels.

Traces of radioactive materials can be found in the body, mainly naturally occurring potassium-40. Potassium-40 is found in the food, soil, and water we ingest. Our bodies contain small amounts of radiation because the body metabolizes the non-radioactive and radioactive forms of potassium and other elements in the same way.

Man-made Sources

A small fraction of background radiation comes from human activities. Trace amounts of radioactive elements have dispersed in the environment from nuclear weapons tests and accidents like the one at the Chernobyl nuclear power plant in Ukraine. Nuclear reactors emit small amounts of radioactive elements. Radioactive materials used in industry and even in some consumer products are also a source of small amounts of background radiation.

Average U.S. Doses and Sources

All of us are exposed to radiation every day, from natural sources such as minerals in the ground, and man-made sources such as medical x-rays. According to the National Council on Radiation Protection and Measurements (NCRP), the average annual radiation dose per person in the U.S. is 6.2 millisieverts (620 millirem) . The pie chart below shows the sources of this average dose.

Most of our average annual dose comes from natural background radiation sources:

• The radioactive gases radon and thoron, which are created when other naturally occurring elements undergo radioactive decay.
• Space (cosmic radiation).
• Naturally occurring radioactive minerals:
  • Internal (in your body).
  • Terrestrial (in the ground).

Another 48 percent of the average American’s dose comes from medical procedures. This total does not include the dose from radiation therapy used in the treatment of cancer, which is typically many times larger.

Scientists measure radiation in different ways. Sometimes, they measure the dose that a person receives from a radioactive source, and sometimes they measure the amount of radioactivity in water, or in soil, or in the air. These measurements are taken to determine if safety actions are needed.

There are different but interrelated units for measuring radioactivity and estimating health effects.

Radioactivity

Radioactivity is a measure of the ionizing radiation released by a radioactive material. Different types of ionizing radiation have the potential to damage human tissue.

A material's radioactivity is measured in becquerels (Bq, international unit) and curies (Ci, U.S. unit). Because a curie is a large unit, radioactivity results are usually shown in picocuries (pCi). A picocurie is one trillionth of a curie. The higher the number, the more radiation released by the material.

Examples:

• The natural radium-226 level of surface water generally ranges from 0.0037 to 0.0185 becquerels per liter (Bq/L), or 0.1 to 0.5 picocuries per liter (pCi/L).¹
• The radium limit in drinking water for daily consumption is 0.185 becquerels per liter (Bq/L), or 5.0 picocuries per liter (pCi/L).²

Unit Conversions and Calculations

Absorbed Dose

Absorbed dose describes the amount of energy deposited per unit mass in an object or person. The units for absorbed dose are gray (Gy, international unit) and rad (rad, U.S. unit).

Examples:

• A dose to the lens of the eyes from a brain CT scan is about 60 milligray (mGy) or 6 rad.
• A dose to the thyroid from a chest CT scan is about 10 milligray (mGy) or 1 rad.³

Unit Conversions and Calculations

Effective Dose

Effective dose takes the absorbed dose (see above) and adjusts it for radiation type and relative organ sensitivity. The result is an indicator for the potential for long-term health effects (i.e., cancer and hereditary effects) from an exposure. It is used to set regulatory limits that protect against long-term health effects in a population. It also allows experts to compare anticipated health effects from different exposure situations. Because this value is a calculated approximation, not a physical quantity, it cannot be used to predict individual health effects. The units for effective dose are sievert (Sv, international unit) and rem (rem, U.S. unit).

Examples:

• The annual radiation dose limit for workers is 0.05 sieverts (Sv) or 5 rem.⁴
• During an emergency, the guidance for when to evacuate or shelter in place is when the total projected dose exceeds 10-50 millisieverts (mSv) or 1-5 rem over the course of four days.⁵

Unit Conversions and Calculations

Key points

• Many factors can change the effects of radiation on your body including the radiation dosage and your age.
• Radiation can damage the DNA in cells, and high doses can lead to cancer later in life.

Overview

We've been studying the effects of radiation on living tissue for more than 100 years. By measuring radiation and understanding its health effects, we can work safely around it.

The radiation dose, or the amount of radiation, is critical to determining the health consequences of radiation. We receive low doses of radiation from our natural environment every day without much danger. We know that very high radiation doses can lead to serious injury or death. Such radiation doses are far above regulatory safety limits.

Facts

High doses of radiation can be serious. We know that radiation at high doses can cause cancer and even lead to death.

How radiation is delivered affects health impact. A dose received over a period of time is less harmful than the same dose received quickly at once. Radiation exposure to one part of the body is less harmful than a dose to the whole body.

Some people are more vulnerable to the effects of radiation, including:

• Developing fetuses (the most vulnerable).
• Infants.
• Children.
• The elderly.
• Pregnant women.
• People with compromised immune systems.

The risk from radiation is higher for young people. This is because they have:

• More cells that are dividing rapidly and tissues that are growing.
• A longer lifespan ahead of them, giving cancers more time to develop.

People may also have individual sensitivity to radiation, even within the same age group.

How radiation impacts your body

Like with many other contaminants or toxins, our DNA (genetic material) is the primary target of radiation.

Radiation can interact with DNA directly and cause damage by breaking bonds in the DNA. It can also harm DNA indirectly by breaking water molecules surrounding the DNA. When these water molecules are broken, they produce unstable ions and other molecules that can damage cells and organs.

Once a cell is damaged, three things can happen:

1. The cell repairs itself and it goes back to normal.
2. The cell damage is not repaired or is incorrectly repaired, so the cell is changed. This change may eventually lead to cancer.
3. There is too much damage to the cell, and the cell dies.

If a few radiation-damaged cells die, your body will recover, and you do not have the risk of those cells potentially turning into cancer. However, widespread cell death, such as that caused by high radiation doses, can lead to organ failure and, ultimately, death.

High doses of radiation can cause Acute Radiation Syndrome (ARS) or Cutaneous Radiation Injuries (CRI). High doses of radiation could also lead to cancer later in life.

Glossary

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

Radiation dose — The amount of radiation that is absorbed by matter, such as the body.

Ionizing radiation has sufficient energy to affect the atoms in living cells and thereby damage their genetic material (DNA). Fortunately, the cells in our bodies are extremely efficient at repairing this damage. However, if the damage is not repaired correctly, a cell may die or eventually become cancerous.

Exposure to very high levels of radiation, such as being close to an atomic blast, can cause acute health effects such as skin burns and acute radiation syndrome (“radiation sickness"). It can also result in long-term health effects such as cancer and cardiovascular disease. Exposure to low levels of radiation encountered in the environment does not cause immediate health effects, but is a minor contributor to our overall cancer risk.

Acute Radiation Syndrome from Large Exposures

A very high level of radiation exposure delivered over a short period of time can cause symptoms such as nausea and vomiting within hours and can sometimes result in death over the following days or weeks. This is known as acute radiation syndrome, commonly known as “radiation sickness.”

It takes a very high radiation exposure to cause acute radiation syndrome—more than 0.75 gray (75 rad) in a short time span (minutes to hours). This level of radiation would be like getting the radiation from 18,000 chest x-rays distributed over your entire body in this short period. Acute radiation syndrome is rare, and comes from extreme events like a nuclear explosion or accidental handling or rupture of a highly radioactive source.

Radiation Exposure and Cancer Risk

Exposure to low-levels of radiation does not cause immediate health effects, but can cause a small increase in the risk of cancer over a lifetime. There are studies that keep track of groups of people who have been exposed to radiation, including atomic bomb survivors and radiation industry workers. These studies show that radiation exposure increases the chance of getting cancer, and the risk increases as the dose increases: the higher the dose, the greater the risk. Conversely, cancer risk from radiation exposure declines as the dose falls: the lower the dose, the lower the risk.

Radiation doses are commonly expressed in millisieverts (international units) or rem (U.S. units). A dose can be determined from a one-time radiation exposure, or from accumulated exposures over time. About 99 percent of individuals would not get cancer as a result of a one-time uniform whole-body exposure of 100 millisieverts (10 rem) or lower. At this dose, it would be extremely difficult to identify an excess in cancers caused by radiation when about 40 percent of men and women in the U.S. will be diagnosed with cancer at some point during their lifetime.

Risks that are low for an individual could still result in unacceptable numbers of additional cancers in a large population over time. For example, in a population of one million people, an average one-percent increase in lifetime cancer risk for individuals could result in 10,000 additional cancers. The EPA sets regulatory limits and recommends emergency response guidelines well below 100 millisieverts (10 rem) to protect the U.S. population, including sensitive groups such as children, from increased cancer risks from accumulated radiation dose over a lifetime.

Exposure Pathways

Understanding the type of radiation received, the way a person is exposed (external vs. internal), and for how long a person is exposed are all important in estimating health effects.

The risk from exposure to a particular radionuclide depends on:

• The energy of the radiation it emits.
• The type of radiation (alpha, beta, gamma, x-rays).
• Its activity (how often it emits radiation).
• Whether exposure is external or internal:
  • External exposure is when the radioactive source is outside of your body. X-rays and gamma rays can pass through your body, depositing energy as they go.
  • Internal exposure is when radioactive material gets inside the body by eating, drinking, breathing or injection (from certain medical procedures). Radionuclides may pose a serious health threat if significant quantities are inhaled or ingested.
• The rate at which the body metabolizes and eliminates the radionuclide following ingestion or inhalation.
• Where the radionuclide concentrates in the body and how long it stays there.

Sensitive Populations

Children and fetuses are especially sensitive to radiation exposure. The cells in children and fetuses divide rapidly, providing more opportunity for radiation to disrupt the process and cause cell damage. EPA considers differences in sensitivity due to age and sex when revising radiation protection standards.

What to know

The radiation thermometer puts common radiation doses in perspective. This resource can help people assess their own risk in the event of a radiation emergency.

Radiation dose

Radiation dose represents the amount of radiation absorbed by the body and is measured in millisieverts (mSv) [pronounced MIH-lee SEE-vert] or rem (1 rem equals 10 mSv). The millisievert unit of measurement is used internationally while the rem is used in the United States.

Radiation thermometer

The thermometer uses a logarithmic scale, where each gray line represents a ten times increase or decrease in the dose, rather than a one unit increase or decrease.

Find below examples of common radiation sources and possible health effects at different doses.

Examples of common radiation sources, dose, and outcomes

100% lethality

The dose that results in death for 100% of those who receive it is 1000 rem / 10000 mSv. People who are close to the site of a radiation emergency may be at risk for this dose.

50% lethality

The dose that results in death for 50% of those who receive it is 400 rem / 4000 mSv. People who are close to the site of a radiation emergency may be at risk for this dose.

Acute radiation syndrome and increased cancer risk

The lowest dose that could cause acute radiation syndrome is 100 rem / 1000 mSv.

Dose for which risk of getting a fatal cancer increases from about 22% (average risk of cancer in United States) to about 27% (derived from).

Damage to blood cells

The dose that causes damage to blood cells is 50 rem / 500 mSv.

Relocation threshold

The recommended threshold for relocating people is 2 rem / 20 mSv. If projected dose from radioactive contamination is greater for the coming year, relocate.

CT scan

The dose received during a typical CT (computerized tomography) scan is 1 rem / 10 mSv.

Average annual dose in the U.S.

Average dose per year for people in the U.S. from

• naturally occurring background radiation – 310 mrem
• medical exposures – 300 mrem
• consumer products – 10 mrem

Chest x-ray

A typical dose of radiation from a chest X-ray is 0.01 rem / 0.1 mSv.

Flight from NYC to LA

A typical dose from high altitude solar and cosmic radiation during a flight from New York City to Los Angeles is 0.0035 rem / 0.035 mSv (derived from).

Dental x-ray

A typical dose of radiation from a dental x-ray (bitewing and full mouth survey) is 0.0005 rem / 0.005 mSv.

Radiation dose in mSv and rem

Key Points

• Radiation is energy and is measured to determine a dose rate (sometimes called ambient radiation) and radiation dose (radiation you absorb).
• Radioactivity is a measure of the amount of radioactive material.
• If you encounter radiation units, equipment, or measurements that you don't understand, ask a radiation safety professional for assistance.

Overview

We quantify radiation by measuring the dose rate and the dose. We determine radioactivity by measuring the energy emitted by the radioactive atoms present and then "count them up." To do these things reliably, we need the proper equipment and trained personnel.

Radiation detection equipment must be maintained to ensure it is working properly. Radiation safety professionals can assist you with using such equipment and interpreting the instrument readings. Seek them out for assistance if needed.

It's all about energy

When working with radiation, we are concerned about the amount of energy the material is emitting. The size, weight, and volume of the source don't necessarily matter.

Depending on the radionuclide (a type of atom with excess nuclear energy), a small amount of radioactive material may give off a lot of radiation. On the other hand, a large amount of radioactive material may give off a small amount of radiation.

Terms to know

• Radioactivity - The amount of radioactive material (radioactive atoms) present at a location or inside something.
• Radiation dose rate - The amount of radiation coming from a source (or in an area) during a period of time, sometimes called ambient radiation levels.
• Radiation dose - The amount of radiation that is absorbed by matter, such as the body.
• Radionuclide - A type of atom with excess neutrons or protons, making it unstable.

Common measurements of radiation

Measuring the amount of radioactivity

We measure the amount of radioactivity by finding out how many radioactive atoms decay every second. These atoms may be giving off alpha particles, beta particles, and/or gamma rays.

The amount of radioactivity is reported in becquerel (Bq), which is the international unit, or the curie (Ci), which is the unit used in the United States. Geiger counters are commonly used to measure the amount of radioactivity, but there are other types of detectors that may be used.

Measuring radiation dose rates

Radiation dose rates in the environment can be thought of as ambient radiation levels.

Ambient radiation levels are reported in gray per hour (Gy/h) or sievert per hour (Sv/h), which are the international units. In the United States, we use roentgen per hour (R/h) or rem per hour (rem/h).

Instruments called pressurized ionization chambers are best suited for measuring ambient radiation levels.

Measuring radiation dose

Radiation dose is the amount of radiation absorbed by the body.

Radiation doses are reported in gray (Gy) or sievert (Sv), which are international units. In the United States, we use rad or rem.

Alarming dosimeters can be used by first responders and safety officers to monitor dose in real time. There are also specialized instruments used by hospitals and laboratories that can measure dose.

Putting radiation dose in perspective

The average dose we receive every year, just from living on Earth, is approximately 3 mSv. Medical procedures add another 3 mSv, on average, bringing the total annual exposure for the average person to around 6 mSv. But, as individuals, the radiation doses we may receive in any one year can vary quite a bit.

There are many things that can influence our radiation dose in any year. Some types of radiation, like natural background radiation, are present all the time. This natural background radiation depends on a number of factors. For example:

• If you live at higher elevation, you receive a higher dose of cosmic radiation.
• If you share a bed with your spouse or partner, you each get a small dose of radiation from the naturally occurring radioactive potassium-40 in each other's body. You irradiate each other during the night.
• You may live in a home that has elevated radon levels.

Medical imaging procedures used in diagnostic exams such as x-rays and CT scans provide a one-time dose. Other medical procedures, such as nuclear medicine, may involve giving you a small amount of radioactive material. In that case, you may emit radiation for up to several days after the exam. The frequency of activities such as medical procedures that provide one-time doses will impact your annual radiation dose.

Radiation is part of our life. Background radiation , coming primarily from natural minerals, is around us all the time. Fortunately, there are very few situations where an average person is exposed to uncontrolled sources of radiation above background. Nevertheless, it is wise to be prepared and know what to do if such a situation arises.

One of the best ways to be prepared is to understand the radiation protection principles of time, distance and shielding. During a radiological emergency (a large release of radioactive material into the environment), we can use these principles to help protect ourselves and our families.

Time, Distance and Shielding

Time, distance, and shielding actions minimize your exposure to radiation in much the same way as they would to protect you against overexposure to the sun:

• Time: For people who are exposed to radiation in addition to natural background radiation, limiting or minimizing the exposure time reduces the dose from the radiation source.
• Distance: Just as the heat from a fire reduces as you move further away, the dose of radiation decreases dramatically as you increase your distance from the source.
• Shielding: Barriers of lead, concrete, or water provide protection from penetrating gamma rays and x-rays . This is why certain radioactive materials are stored under water or in concrete or lead-lined rooms, and why dentists place a lead blanket on patients receiving x-rays of their teeth. Therefore, inserting the proper shield between you and a radiation source will greatly reduce or eliminate the dose you receive.

Radiation Emergencies

In a large scale radiological release, such as a nuclear power plant accident or terrorist incident, the following advice has been tested and proven to provide maximum protection.

If a radiation emergency occurs, you can take actions to protect yourself, your loved ones and your pets: Get Inside, Stay Inside andStay Tuned. Follow the advice of emergency responders and officials.

Get Inside

In a radiation emergency you may be asked to get inside a building and take shelter for a period of time.

• This action is called " sheltering in place ."
• Get to the middle of the building or a basement, away from doors and windows.
• Bring pets inside.

Stay Inside

Staying inside will reduce your exposure to radiation.

• Close windows and doors.
• Take a shower or wipe exposed parts of your body with a damp cloth.
• Drink bottled water and eat food in sealed containers.

Stay Tuned

Emergency officials are trained to respond to disaster situations and will provide specific actions to help keep people safe.

• Get the latest information from radio, television, the Internet, mobile devices, etc.
• Emergency officials will provide information on where to go to get screened for contamination.

Key points

• Health effects from radiation vary depending on a number of factors.
• Community reception centers will check you for radiation contamination.
• If exposed to radiation, be aware of symptoms of acute radiation syndrome, including skin burns, nausea, or vomiting.
• Do not go outside until an emergency official says it is safe.

Health effects due to radiation exposure

The health effects of radiation depend on

• The amount of radiation absorbed by the body (the dose)
• The type of radiation
• How the radioactive material got in or on the body
• The length of time a person was exposed

If you were exposed to a small amount of radiation, you will not see any health effects right away. You may not have any long-term health effects.

Depending on the radiation levels received, radiation health experts may monitor people affected by radiation emergencies for any medical issues.

What to look out for

Acute radiation syndrome (ARS) is caused by exposure to large amounts of radiation in a short time. If you have any of the following symptoms after radiation exposure, you should seek medical attention as soon as it is safe:

• Skin burns
• Nausea
• Vomiting

Symptoms can appear within minutes to several days after you were exposed to large amounts of radiation.

If you experience ARS, you may develop Cutaneous Radiation Injuries (CRI). Not everyone who develops CRI will have ARS.

Symptoms of CRI can appear from a few hours to several days after exposure.

The early signs and symptoms of CRI include

• Itchiness
• Tingling
• Skin redness (erythema)
• Swelling caused by a buildup of fluid (edema)

Prevention steps and strategies

Before you move‎

The best way to prevent radiation injuries and illness is to

• Get inside as soon as possible
• Stay away from the radioactive material outside
• Shower or wash once inside (self-decontamination)

Treat non-radiation related cuts, bruises, or injuries with first aid. Keep cuts and abrasions covered when washing to keep radioactive material out of the wound.

Emergency officials will set up community reception centers to check people for radiation exposure and contamination.

Medical emergencies‎