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What is Radiation?

Radiation is energy that travels.

Energy is released in chemical and nuclear reactions. Some of this energy is released as radiation. Nuclear forces are strong, so radiation released by nuclear reactions usually has more energy than radiation released by chemical reactions. There are two main forms of radiation: electromagnetic radiation and particle radiation.

  • Electromagnetic radiation is a wave of energy, like light rays. The electromagnetic radiation released by nuclear forces-X-rays or gamma rays—has much more energy than visible light rays.
  • Sub-atomic particles, like electrons, protons and neutrons can also carry energy. These particles move more slowly than light, so the energy does not travel as quickly.

Your body can absorb radiation. Different kinds of radiation are absorbed differently. For example X-rays are absorbed by bones, but not by muscle.

Radiation with a lot of energy can damage your body, especially if it is absorbed inside your body rather than by the skin.

Gamma rays are more dangerous than X-rays because they have more energy. This also makes them penetrate much deeper into your body. In fact many gamma rays will pass right through your body (but the ones that are absorbed will do more damage.)

Heavy alpha rays have more momentum than beta rays, so they can do more damage. However, alpha rays from outside your body are much more likely to be absorbed by the skin than beta rays. Alpha rays that are released by radioactive elements inside your body can be very dangerous.

Neutrons are not as heavy as alpha rays but because they do not experience the electric force they are able to go a long way into your body. This makes neutrons extremely dangerous to living organisms.

Background Radiation

Everyone is exposed to some radiation. This background radiation comes both from natural sources as well as from human activities.

Natural radiation is all around us. Radioactive elements are found everywhere—in the air that we breathe, the food that we eat, and in the ground around us. Radioactive gases in air are the most dangerous, providing over 50% of the background radiation, while radioactive elements in food and in the ground each contribute about 10%.

Cosmic rays from outer space also produce about 10% of the background radiation. This is increased when you climb a mountain, or take a plane flight.

The activities of humans can also increase exposure to radiation. X-rays and other medical techniques can increase your exposure to radiation by 20%.

Some building materials have a higher than average concentrations of radioactive elements. Explosions of nuclear weapons in the last sixty years have also added to background radiation. Both of these sources increase exposure to radiation by around 1%.

However, the biggest exposure to radiation by far comes from the radioactive elements in cigarettes. Smoking can increase exposure to radiation by 400%!

Some workers have jobs that increase their exposure to radiation above these levels. When this exposure is known, precautions can be taken, such as wearing protective clothing. When exposure to radiation is unknown, or radioactive materials are disposed of improperly, high risks of damage from radiation can be incurred.


Old x-ray
magnifyX-Rays are invisible radiation


Cosmic rays colliding with the atmosphere
magnifyCosmic rays colliding with the atmosphere


Radiation medicine image of the brain.
magnifyRadiation medicine image of the brain.


A nuclear explosion
magnifyA nuclear explosion


Scientist in a lab
magnifyScientist in a lab
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