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What is radiation?
"Radiation" is a broad term and includes things such as light and radio waves. In the context of radioactivity, we are referring to the disintegration of atoms. Radioactivity occurs naturally in the earth, and such naturally occurring radioactive materials are around us all the time in building materials, food, the air we breathe and our own bodies. Such radiation is referred to as "background radiation" and includes cosmic radiation.
On a global average, our background radiation exposure due to all natural sources amounts to about 2.4 mSv a year (IAEA figures), though this figure can vary, depending on the geographical location, by several hundred percent. For example, the average Australian would receive about 1.5mSv per year of background radiation. Someone living at a higher altitude, such as a person living in Katoomba, would receive about 2.5 mSv per year.
Basically there are three different types of ionising radiation: alpha, beta and gamma.
Alpha radiation Alpha radiation can be absorbed by thin materials like paper, but can be harmful if ingested. A natural alpha emitter is uranium-238, which has a half-life of 4.5 billion years - a half-life being the rate of decay or the time required for the radioactivity to be reduced by one-half. Half-lives can vary from fractions of seconds to billions of years.
Beta radiation Beta radiation can be natural or man-made. It passes through paper, so must be absorbed by thicker materials. Materials containing beta radioactivity can deliver a radiation dose from inside or outside the body. Carbon-14 is an example of a beta emitter. It has a half-life of 5700 years, which makes it very useful for dating materials.
Gamma radiation Gamma radiation is the most penetrating kind of radiation and can also deliver a dose from inside or outside the body. Technetium-99m, which ANSTO produces for diagnostic medicine, is a gamma emitter with a half-life of just six hours.
For more information see our Ionising Radiation brochure.