Natural background radiation
Australians are exposed to radiation from a variety of natural and artificial sources. We are all exposed constantly to ionising radiation from a variety of natural and artificial sources.
The sun is a major source of 'cosmic radiation'. Skiing at high altitudes and airline flights will increase our exposure to cosmic radiation. Many buildings also emit ionising radiation simply because the materials that were used to build them (clay bricks, granite etc) are naturally radioactive. These are all examples of 'background radiation'.
Average exposures to background radiation
- In Australia people receive about 1.5 - 2.0 'millisieverts' of ionising radiation every year. This is natural background radiation. Low exposure to ionising radiation is not harmful.
- Passengers on high-altitude flights get more exposure to cosmic radiation than at ground level. For example, if you flew return from Sydney to Los Angeles you would get 0.16 millisieverts of radiation dose.
- Because granite emits more radiation than other materials, a home with granite tiles would expose the occupants to 1.0 millisieverts of radiation annually.
- Some X-rays and similar procedures provide higher radiation doses, with a typical X-ray/CT scan of your head exposing you to 2.6 millisieverts.
- As a comparison, radiation workers at ANSTO receive, on average, an exposure above natural background levels of 0.6 millisieverts a year – well under the maximum occupational limit of 20 millisieverts annually.
Naturally occurring radioactive materials
Radioactive materials which occur naturally and expose people to radiation occur widely, and are known by the acronym 'NORM'. Exposure to NORM is often increased by human activities, e.g., burning coal, making and using fertilisers, oil and gas production. Another NORM issue relates to radon exposure in homes, particularly those built on granitic ground. The accumulation of radon in homes may need to be controlled by ventilation.