What is radiation?

Radiation is the transfer of energy from a radioactive source, by way of electromagnetic waves or fast-moving subatomic particles.

Radiation is an everyday experience: the sun radiates both electromagnetic waves (light) and subatomic particles (the solar wind), which are essentially the same components of the radiation from nuclear technologies. However, there are key differences between the two.

The electromagnetic waves radiated by the sun have many different wavelengths, which is a measure of their energy. Some of those wavelengths have high enough energy to damage living tissues, but most of those are absorbed by earth’s atmosphere – but not all, which is why people wear sunscreen to avoid a sunburn. The light that passes through the atmosphere has a much more limited set of wavelengths, which is visible as light. Earth’s atmosphere also deflects the higher-energy particles streaming out of the sun, though this is something that astronauts have to be concerned about.

Radiation becomes a concern on earth when people or the environment are exposed to particles or electromagnetic waves that are energetic enough to break apart the molecules that make up our bodies, causing health problems.

These types of radiation are called “ionizing” radiation, because they have enough energy to knock an electron out of its orbit around an atom – creating an ion. Humans are exposed to many other common types of radiation that are non-ionizing, such as radio waves, microwaves, and sunlight.

Ionizing radiation

There are four main types of ionizing radiation, each with its own properties:

  • Alpha particles are helium nuclei – two protons and two neutrons. They are the largest and heaviest, but also the easiest to protect against, because they are stopped easily by a sheet of paper or the dead outer layer of human skin.
  • Beta particles are fast-moving electrons and positrons, which are much smaller than alpha particles – but are also very easily stopped, by plastic or the deeper layers of the skin.
  • Gamma rays have no mass; they are pure energy, in the form of electromagnetic waves that have very short wavelengths – and therefore much more energy than visible light has. Shielding gamma rays is normally accomplished by heavy metals such as lead; only thin layers are needed to stop the vast majority of gamma rays, although some will get though.
  • Neutrons are subatomic particles that are larger than beta particles and smaller than alpha particles, but have no charge; while these characteristics make neutron radiation able to penetrate lead, neutrons are stopped by the water and concrete common in nuclear reactors.

Types of radiation

Ionizing radiation is part of the natural environment: some radiation from the sun and the cosmos is not filtered out by the atmosphere, while decaying isotopes in the earth’s crusts emits radiation. Radioactive isotopes naturally exist at trace levels in the air, drinking water, and food. Occasionally, people will choose an additional dose of radiation, for example through x-ray technology, because the health benefits are a reasonable trade-off against exposure that is usually less than 1% of the annual natural dose.