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.

The actual amount of 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 when working or experimenting with radioactive sources and discount it from their results.

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

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

A source that one particle per second has an activity of one Bq. However, this particle could be or 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 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 potassium 0.000000098 Sv 0.000098 mSv Exposure for cabin crew on airliners (per year) 0.0016 Sv 1.6 mSv 6 months on the International Space station 0.08 Sv 80 mSv Highest dose to a worker during Fukushima disaster 0.67 Sv 670 mSv Typical fatal dose 10 Sv 10,000 mSv
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