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Radiation is when energy moves through space away from a source (of radiation). There are two broad classes of radiation: ionizing radiation which comes from radioactive materials and x-ray machines and non-ionizing radiation (usually electromagnetic radiation) which comes from other sources. Ionizing radiation, which carries a large energy in each particle, can change things that it hits, hurting people or animals or causing chemical changes. Non-ionizing radiation does not cause microscopic damage, but some types can cause chemical changes or make things hotter.

There are many different ways that energy can travel through space in this way. One way is in the form of shifting electrical and magnetic fields. This is why some common types of radiation are referred to as Electromagnetic radiation, also known as light. (A different way to think of electromagnetic radiation is as a stream of particles of energy called photons.) Another way that radiation can travel is in the form of tiny particles. These are pieces of atoms, like neutrons or protons (please see the article on atoms for more information). When radiation is made up of quickly moving particles (like pieces of atoms), it is referred to as particle radiation.
People in radiation protective outside suits.

Many people are already familiar with different kinds of electromagnetic radiation/light. Scientists categorize this type of radiation based on its wavelength and frequency. Some kinds of electromagnetic radiation are:

  • Radio waves: This is the kind of electromagnetic radiation with the highest wavelength. Radio waves are used to send and receive communications.
  • Micro-waves: This is a special kind of radio wave that is used by a microwave oven to warm up food. Microwaves are also used for communications, as weapons, and to move electrical power from one place to another.
    • Radar waves: This is also a kind of radio wave that is used to wank off airplanes in the sky and ships in the ocean. Radar is also used to see changes in weather.
  • Infrared waves: Most objects at room temperature let off infrared radiation. Although humans cannot see it, special types of cameras can pick up this kind of radiation. Usually, the hotter something is, the more infrared radiation it lets off, which means that these special cameras can see hot things, even behind walls.
  • Visible light: This is the radiation that we see all around us as what most people call "light."
  • Ultraviolet light: This is a type of radiation with more energy than visible light that gives people a sunburn. Ultraviolet light is also used to kill bacteria and to make some kinds of invisible ink visible.
  • X-rays and Gamma rays: These are extremely strong rays that are commonly used in medicine to photograph the interior of the body and treat cancer. However, in too large amounts, they are very dangerous to life.

Danger from radiation

Most people hear terms like radiation and immediately think of it as a bad or dangerous thing. It turns out that only certain types of radiation are ordinarily harmful to humans. For example, ultraviolet radiation can give people sunburns. X-rays and gamma rays can make a person sick, or even die if they are exposed to them for a very long time. Some types of particle radiation can also make people sick and lead to burns. Any type of radiation that causes changes in the world like these is referred to as ionizing radiation. If radiation does not carry high enough levels of energy, though, then these changes will not happen when something is hit by the radiation. This is referred to as non-ionizing radiation, which is not as dangerous.

One can distinguish between various types of radiation by looking at the source of the radiation, its wavelength (if the radiation is electromagnetic), the amount of energy being carried, any particles involved, etc. Radioactive material is a physical material that emits radiation. Uranium and plutonium are examples of radioactive materials. The atoms they are made of tend to fall apart and give off different kinds of radiation, like gamma rays and lots of types of particle radiation.

Different Ionizing Radiations by type

Ionising radiation can kill living things. It can cause genetic mutations, as shown by H.J. Muller. It can destroy cells in the body which divide, and thus indirectly kill a person.

Different Non-Ionizing Radiations by type

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