How Radiation Works

Visible light is part of the electromagnetic spectrum. 
Visible light is part of the electromagnetic spectrum. 
Michael Duva/Getty Images

Say the word "radiation" to three different people, and you'll probably get three different reactions. Your aunt may tell you how radiation destroyed her cancer. Your neighbor might mention the "duck and cover" procedures of his day. And your comics-loving friend will explain how gamma rays turned Bruce Banner into The Hulk. Radiation comes in m­any forms and is all around us, all the time. Sometimes it's dangerous; sometimes it's not.

Radiation is both natural and man-made. Our bodies are exposed to natural radiation every day -- from soil and underground gases to cosmic radiation from the sun and outer space. We're also exposed to radiation from our own inventions -- medical procedures, televisions, cell phones and microwave ovens. Radiation isn't necessarily always dangerous. It depends on its strength, type and the length of exposure.

Most people will tell you Marie Curie discovered radiation, along with her husband and research partner Pierre. And that's right -- sort of. Curie actually discovered the element radium in 1898, an accomplishment that would make her the first female recipient of the Nobel Prize. However, three years earlier in 1895, a scientist named Wilhelm Röntgen first discovered X-rays and the phenomenon of radioactivity (a term later coined by Curie, based on the Latin word for "ray"). Soon after Röntgen's discovery, a French scientist named Henri Becquerel attempted to figure out where X-rays came from, and in the process found that uranium emitted a powerful "ray." Marie Curie based her doctoral research on Becquerel's findings, which led to her discovery of radium [source: Vaught].

Radiation is energy that travels in the form of waves (electromagnetic radiation) or high-speed particles (particulate radiation). Particulate radiation happens when an unstable (or radioactive) atom disintegrates. Electromagnetic (EM) radiation, on the other hand, has no mass and travels in waves. EM radiation can range from very low energy to very high energy, and we call this span the electromagnetic spectrum. Within the EM spectrum, there are two types of radiation -- ionizing and non-ionizing.

Feeling a bit overwhelmed? Don't worry, we'll explain all this in detail on the next few pages.

The Electromagnetic Spectrum

Ultraviolet rays from the sun are a form of radiation.
Ultraviolet rays from the sun are a form of radiation.

Electromagnetic (EM) radiation is a stream of photons, traveling in waves. The photon is the base particle for all forms of EM radiation. But what's a photon? It's a bundle of energy -- of light -- always in motion. In fact, the amount of energy a photon carries makes it sometimes behave like a wave and sometimes like a particle. Scientists call this wave-particle duality. Low-energy photons (such as radio) behave like waves, while high-energy photons (such as X-rays) behave more like particles. You can read more about how photons work in How Florescent Lamps Work.

EM radiation can travel through empty space. This differentiates it from other types of waves, such as sound, which need a medium to move through. All forms of EM radiation reside on the electromagnetic spectrum, which ranks radiation from lowest energy/longest wavelength to highest energy/shortest wavelength. The higher the energy, the stronger, and therefore more dangerous, the radiation. The only difference between a radio wave and a gamma ray is the energy level of the photons [source: NASA]. Below is the electromagnetic spectrum at a glance.

Radio: Radio waves have the longest wavelength in the electromagnetic spectrum (up to a football field long). They are invisible to our eyes. They bring music to our radios, sound and picture to our televisions, and carry signals to our cell phones. Cell phone waves are shorter than radio waves, but longer than microwaves.

Microwaves: Also invisible, we use microwaves to heat our food quickly. Telecommunications satellites use microwaves to transmit voice through the phone. Microwave energy can penetrate haze, clouds or smoke, and thus is useful for transmitting information. Some microwaves are used for radar, like the Doppler radar your weatherman uses on the news. The entire universe has faint cosmic microwave background radiation -- something scientists connect to the Big Bang Theory.

Infrared: Infrared lies between the visible and invisible portions of the EM spectrum. Your remote control uses infrared light to change the channel. We feel infrared radiation every day via the sun's heat. Infrared photography can detect temperature differences. Snakes can actually detect infrared radiation, which is how they are able to locate warm-blooded prey in total darkness.

Visible: This is the only part of the electromagnetic spectrum we can see. We see the different wavelengths in this band of the spectrum as the colors of the rainbow. The sun, for example, is a natural source of visible waves. When looking at an object, our eyes see the color of light reflected, and all other colors are absorbed.


Ultraviolet: Ultraviolet (UV) rays are what cause us to become sunburned.  Humans can't see UV rays, but some insects can. Our atmosphere's ozone layer blocks most UV rays. However, as our ozone layer depletes due to use of chlorofluorocarbons (CFCs), UV levels are increasing. This can lead to health effects like skin cancer [source: EPA].

X-rays: X-rays are very high-energy light waves. We're most familiar with their use in a doctor's office, but X-rays also naturally occur in space. But don't worry, X-rays can't penetrate from outer space to the Earth's surface. Read more in How X-rays Work.

Gamma rays: Gamma rays have the most energy and shortest wavelength of the entire spectrum. Nuclear explosions and radioactive atoms generate these rays. Gamma rays can kill living cells, and medical professionals sometimes use them to destroy cancerous cells. In deep space, gamma ray bursts occur daily, but their origins are still a mystery.

Read on to find out the difference between non-ionizing and ionizing radiation.

Non-ionizing Radiation

Microwave drum tower at dusk in Baltimore, Md.
Microwave drum tower at dusk in Baltimore, Md.
Greg Pease/Getty Images

Radiation is broken down into two types: non-ionizing and ionizing. On the electromagnetic (EM) spectrum, this break occurs between infrared and ultraviolet. Drilling down further, ionizing radiation comes in three main types: alpha particles, beta particles and gamma rays. We'll discuss these types of radiation in more detail later in this article.

Non-ionizing radiation is relatively low-energy radiation that doesn't have enough energy to ionize atoms or molecules. It's located at the low end of the electromagnetic spectrum. Non-ionizing radiation sources include power lines, microwaves, radio waves, infrared radiation, visible light and lasers. Although considered less dangerous than ionizing radiation, overexposure to non-ionizing radiation can cause health issues. Let's take a look at some examples of non-ionizing radiation and the safety issues surrounding them.

Extremely low frequency (ELF) radiation is the radiation produced by things like power lines or electrical wiring. There are health concerns associated with magnetic field exposures near power lines, and this issue is very controversial. Obviously, ELF radiation surrounds us every day, but hazardous exposure depends on the strength of the ELF at the source, as well as the distance and duration of exposure. Research on ELF radiation focuses on cancer and reproductive issues. There is no definitive link between ELF radiation and illness, but studies have shown some preliminary connections [source: WHO].

Radio frequency (RF) and microwave (MV) radiation come most commonly from radios, televisions, microwave ovens and cell phones. Both RF and MV waves can interfere with pacemakers, hearing aids and defibrillators, and people should take appropriate precautions. In recent years, concerns about cell phone radiation have made headlines. Although there is no proven link between cell phone usage and health issues, the potential is there. Again, it's all about exposure. Large amounts of RF exposure can heat tissue, which can damage skin or eyes and raise body temperature. Some experts recommend using a headset or hands-free device if you use your cell phone frequently and for long periods [source: FCC]. You can find out more about cell phones and radiation in our article How Cell Phone Radiation Works.

Our skin and eyes absorb infrared radiation (IR) as heat. Overexposure to IR can result in burns and pain. Ultraviolet (UV) radiation overexposure concerns us because there are no immediate symptoms. However, effects can develop quickly afterward in the form of a sunburn or worse. Overexposure to UV radiation can lead to skin cancer, cataracts and a compromised immune system [source: EPA]. Besides sunlight, UV sources include black lights and welding tools.

Lastly, lasers emit IR, visible and UV radiation. They can be quite dangerous to the eyes and skin. People who work with lasers should wear protective gear on the eyes, hands and arms.

Keep reading to learn about high-energy ionizing radiation.

Ionizing Radiation

X-ray of a young boy's torso.
X-ray of a young boy's torso.
Sami Sarkis/Getty Images

Similar to non-ionizing radiation, ionizing radiation is energy in the form of particles or waves. However, ionizing radiation is so high in energy it can break chemical bonds -- meaning it can charge (or ionize) an atom that interacts with it. At a lower energy, it may strip off a couple of electrons. At a higher energy, it can destroy the nucleus of an atom. This means that when ionizing radiation passes through the tissues of the body, it actually has enough energy to damage DNA. It's why gamma rays, for example, are good at killing cancer cells through radiation treatment.

Ionizing radiation is given off by radioactive material, very high-voltage equipment, nuclear reactions and stars. It's both natural and man-made. A natural source of ionizing radiation is radon, a radioactive material found underground. X-rays are a good example of man-made ionizing radiation.

The three types of ionizing radiation we're going to discuss here are alpha particles, beta particles and rays.

Particulate radiation involves fast-moving, small particles that have energy and mass. When an unstable atom disintegrates, it produces particulate radiation, including alpha and beta particles. For example, when radioactive elements like uranium, radium and polonium decay, they release radioactive alpha particles. These particles, made up of protons and neutrons, are large and can only travel a short distance -- in fact, they can be stopped with just a piece of paper or even your skin. However, inhalation or ingestion of alpha particles can be very dangerous. Once inside your body, alpha particles expose your tissues to radiation.

Beta particles, on the other hand, are fast-moving electrons. They can travel and penetrate more than alpha particles. Beta particles can be stopped or reduced by a layer of clothing or a substance like aluminum (so think twice the next time you laugh at the guy on the corner wearing a protective tinfoil hat!). However, some beta particles have enough energy to penetrate the skin and cause damage like burns. As with alpha particles, beta particles are quite hazardous if inhaled or ingested.


Gamma rays are a type of electromagnetic radiation, but they still emit ionizing radiation because of their high energy. Gamma rays often accompany alpha and beta particles. Unlike alpha and beta particles, they are extremely penetrating. In fact, several inches of lead or even a few feet of concrete are required to stop gamma rays. They are a radiation hazard for the entire body, meaning that although they will pass through you, your tissue will absorb some rays. Gamma rays occur naturally in minerals like potassium-40. Don't stop taking your vitamins just yet, though. The radioactive isotope of potassium occurs at an extremely low concentration, and potassium is necessary for good health [source: HPS].

X-rays are essentially the same as gamma rays, but their origin is different. Where gamma rays come from inside the nucleus of an atom, X-rays come from processes outside the nucleus. X-rays come from a change in the electron structure of an atom and are mostly machine-produced. They aren't quite as penetrating as gamma rays, and just a few millimeters of lead can stop them. That's why you wear a "lead apron" when receiving medical X-rays.

Overexposure to ionizing radiation can cause mutations in your genes, which causes birth defects, a raised risk of cancer, burns or radiation sickness [source: NLM].

Is this information freaking you out? Then let's get to radiation exposure on the next page.

Radiation Exposure

Radiation is everywhere. It's been part of our environment since the planet was born. Radiation exists in the atmosphere, the ground, the water and even within our own bodies. It's called natural background radiation, and it's perfectly safe.

Radiation affects your body by depositing energy in your tissues, which can cause cell damage. In some cases, this won't cause any effect. In others, the cell can become abnormal and later malignant. It depends on the strength and duration of the exposure. In the rare occurrence of a huge amount of radiation exposure in a short time, death can occur in a matter of days or hours. We call this acute exposure. Chronic exposure, on the other hand, is frequent exposure to low doses of radiation, over a long period. There can be a delay between initial exposure and consequent health effects. To date, the best information we have about health risk and radiation exposure comes from the survivors of the atomic bomb in Japan and people who work with radiation every day or receive radiation as medical treatment.

We measure amounts of radiation exposure in units called millirem (mrem). Higher readings are measured in mSv, which you can multiply by 100 to get mrem. In the United States, people receive an average annual dose of about 360 mrem. More than 80 percent of this dose comes from natural background radiation [source: DOE]. However, outside considerations greatly affect the average dose. Where and how you live affects the amount of radiation exposure you receive. For example, people who live in the Pacific Northwest part of the United States typically only receive about 240 mrem from natural and man-made sources. However, people in the Northeast receive up to 1700 mrem per year, mostly due to radon that is natural to rocks and soil. Is 1700 mrem safe? Take a look at the sidebar to see.

So what do you do if you're exposed? Find out on the next page.

What to Do If You're Exposed to Radiation

A nuclear power plant accident could leak harmful radiation into the atmosphere.
A nuclear power plant accident could leak harmful radiation into the atmosphere.
Pete Turner/Getty Images

Many movies and books use threats from radiation, such as nuclear accidents and bombs, as fodder for thrill and chills. But what's real and what's not? It's probably safe to say that zombies won't rise up and take over the planet. We think. But radiation poisoning and sickness can and does happen. Radiation can leak into the environment in several ways -- a nuclear power plant accident, an atomic bomb explosion, accidental release from a medical or industrial device, nuclear weapons testing, or terrorism (like a dirty bomb). When we talk about radiation exposure here, we're mostly talking about the very rare occurrence of a large-scale release of radiation.

Every community has a radiation disaster plan in place. Your local officials should be trained in preparedness and will provide instructions should such an emergency occur. During a radiation emergency, the Centers for Disease Control and Prevention (CDC) may recommend you stay inside your home rather than evacuate. This is because the walls of your home can actually block some of the harmful radiation. The safest room in the house is the one with the least windows, possibly your basement or bathroom.

If you work around radiation and radioactive materials, there are mandates on the amount of radiation to which you can be exposed. Depending on the industry in which you work, there are also precautions like safety gear, masks, gloves and lead-lined aprons.

In the event of a radiation emergency, the first thing to figure out is if you are contaminated. If you have radioactive materials on or inside your body, you're contaminated. Contamination can quickly spread -- you'll shed external contaminants as you move about and release bodily fluids. The CDC recommends the following steps to limit contamination:

  1. Get out of the immediate area quickly.
  2. Remove your outer layer of clothing.
  3. Place clothing in a plastic bag or away from others.
  4. Wash all exposed parts of your body.
  5. Internal contamination may call for medical attention.

[source: CDC]

If you're exposed to radiation, medical personnel can evaluate you for radiation sickness or poisoning through symptom checks, blood tests, or a Geiger counter, which can locate radioactive particles. Depending on the severity of exposure, there are different types of medical treatment. Decontamination is the first step, and that may be all you need. Blood tests may be recommended every year or so to check for late-developing symptoms.


There are also pills you can take to reduce symptoms of exposure. You may have heard of people taking potassium iodide tablets in a nuclear emergency. These tablets prevent radioactive iodine from concentrating in your thyroid. It's important to understand that potassium iodide offers no protection from direct radiation exposure or other airborne radioactive particles. Prussian blue is a type of dye that will bind to radioactive elements like cesium and thallium. It will speed up your body's elimination of radioactive particles, reducing the amount of radiation your cells might absorb. Diethylenetriamine pentaacetic acid (DTPA) binds to the metal in radioactive elements like plutonium, americium and curium. The radioactive particles pass out of the body in urine, again reducing the amount of radiation absorbed.

For more information about radiation, expose yourself to the links on the next pa­ge.

Related HowStuffWorks Articles

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