Naturally occurring radioactivity is in the air we breathe, the food we eat and the buildings we live in.
What is natural background radiation?
How much background radiation is there in Australia?
What about artificial sources of radiation?
Is artificial radiation more dangerous than natural radiation?
Natural background radiation is the ionising radiation in the environment that all living species are exposed to every day. The largest source of radiation exposure comes from external exposure to natural radioactivity in rocks and soil (terrestrial radiation) and inhalation of radon gas that seeps from the ground into all buildings. There are also significant contributions from cosmic radiation and naturally occurring radioactivity in food and in the body.
The amount of background radiation present depends on many factors, such as the type of soil and rock present, altitude, latitude and diet. The range of radiation exposure is highly variable, however on average Australians are exposed to 1.5 mSv each year from natural sources. This is about the same amount of radiation received from 75 chest X-rays.
Sometimes artificial sources of radiation are also included as ‘background’ radiation. Medical diagnostic tests and treatments are the largest source of artificial (or man-made) radiation exposure in Australia. Figure 1 compares the average annual exposure to some of the different types of radiation in Australia.
The damaging effects of ionising radiation come from the energy deposited in tissue by the radiation. Although different types of ionising radiation have different patterns of energy release and penetrating power, there is no general property that makes artificial ionising radiation different or more damaging than the ionising radiation that comes from natural radioactive material. This means that we can make direct comparisons between exposures from artificial sources of ionising radiation and those from natural sources.
Harmful tissue reactions (acute or deterministic effects) occur when doses are high (greater than about 500 mSv). These effects occur shortly after exposure (minutes to weeks) and can include sterility, skin burns and acute radiation syndrome. Death can occur at very high doses.
There have been many large scale studies worldwide of cancer risk in people arising from radiation exposure. The risk from exposure to high radiation doses is relatively well quantified, but for low radiation exposures the scientific evidence for increased health risk is more limited (see Figure 2). While there is a possible increased risk of cancer and hereditary effects at low radiation doses or for radiation delivered over a long period of time, these effects are not always detectable in scientific studies. However, their likelihood increases as dose increases.