Background radiation

Radioactive materials occur naturally and, as a result, everyone is exposed to a low-level of radiation every day. This exposure comes from a mixture of natural and man-made sources.

Pie chart looking at sources of background radiation, these are from: Radon gas, Buildings, cosmic rays, food and drink and man-made. Man-made is broken down in another pie chart.

The actual amount of radiation that a person is exposed to depends on where they live, what job they do and many other things.

Scientists must always take into consideration the amount of background radiation when working or experimenting with radioactive sources and discount it from their results.

Background radiation affects everyone mainly by irradiation, but a small amount is from being contaminated by radioisotopes in the food and drink that is consumed.

Measuring amounts of radiation

The simplest measure of radioactivity is the Becquerel (Bq). This is a measure of the activity of the nucleus. The activity is the number of decays per second from an unstable nucleus.

A source that emits one particle per second has an activity of one Bq. However, this particle could be alpha or beta and would, therefore, have a different effect on a person’s body.

  • a beta particle has a lot of energy but may not cause a lot of damage because of its low ionisation power
  • an alpha particle will have less energy but will cause more damage in a shorter distance because it is bigger

The Sievert (Sv) is the unit to measure radiation dose and is the amount of damage that would be caused by the absorption of 1 joule of energy in each kilogram of body mass.

Typically, absorption is less than 1 Sv, so milliSieverts (mSv) are often used instead. 1,000 mSv = 1 Sv.

Some example doses are shown below:

Eating a banana that contains radioactive potassium0.000000098 Sv0.000098 mSv
Exposure for cabin crew on airliners (per year)0.0016 Sv1.6 mSv
6 months on the International Space station0.08 Sv80 mSv
Highest dose to a worker during Fukushima disaster0.67 Sv670 mSv
Typical fatal dose10 Sv10,000 mSv
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