All living things are exposed to natural ionising radiation from the environment. We normally do not think about this exposure to radiation because it comes from things we accept in our everyday lives. Although there is worldwide variation in the levels, the reality is that we have always been and, will always be, exposed to background radiation from natural sources. In Australia, each of us receives an average dose of 1.7 mSv per year from a typical Australian lifestyle. Globally this ranges from 1 to 13 mSv per year.
What are the sources?
Rocks and soil
Most of us have heard of uranium, but little about thorium. These two elements occur naturally on our planet in varying concentrations since the formation of the Earth. We are familiar with uranium mines where concentrations exist naturally at higher levels, however, there are small amounts of uranium and thorium everywhere. These elements undergo radioactive decay and this process produces more radioactive elements until the chain of decays leads to a final element that is not radioactive. Another major contribution is from a radioactive potassium-40. Potassium is an essential life-sustaining element but a small fraction of potassium is naturally radioactive. It too has existed since the formation of the Earth. Rocks containing these elements lead to an exposure, just by being near them. Further, rocks and stone are also in building materials. Rocks exposed to weather and water erode over time. This causes these elements to dissolve and form part of the soil and transfer into water in lakes, rivers and oceans.
Food and water
Food grown in soil, animals that live in water and animals that feed on plants and other animals all take in these elements as part of living in their environment. It follows naturally that all human food sources, including drinking water result in us ingesting these elements when we eat.
Radon
Radon is a naturally occurring radioactive gas, which has no smell, colour or taste. It comes from the radioactive decay of uranium and thorium, which is present in small amounts in rocks and soil. Radon is chemically inert, so it can easily escape from the ground into the air where it can be inhaled. Every breathe we take results in a small exposure to radon gas.
Space
The sun, just like all of the stars, is essentially a gigantic nuclear reactor changing one element into another as they burn their fuel to supply heat and light needed to sustain life. This process results in the production of a large amount of ionising radiation known as cosmic radiation. The Earth’s atmosphere shields us from most of this cosmic radiation. Exposure to the small amount that makes it to the surface varies mostly due to altitude and latitude. In other words, if you live high in mountains and closer to the north or south poles your exposure will be higher than at sea level near the equator. The highest exposure to cosmic radiation occurs when we fly.
More information on ionising radiation and your health can be found on our website
Human’s exposure to ionising radiation
| Source of exposure | Exposure per year (mSv) |
|---|---|
| One CT (computed tomography) scan to the chest | 5 |
| Cosmic radiation exposure of domestic airline pilot | 2 |
| Total natural radiation in Australia | 1.7 |
| Australian uranium mining workers | 1 |
| One return flight from Melbourne to London a year | 0.11 |
| One chest X-ray (two views) a year | 0.06 |
| Nuclear fallout (from atmospheric tests in the 1950s and 1960s) | 0.0 |
World average of natural background ionising radiation
| Source of exposure | Exposure per year (mSv) |
|---|---|
| Inhalation (radon gas) | 0.2-10 |
| External terrestrial | 0.3-1 |
| Ingestion | 0.2-1 |
| Cosmic radiation | 0.3-1 |
| Total natural | 1-13 |
