WHAT IS A RADIATION DOSE?
A radiation dose is an amount of ionizing radiation that is absorbed by your body. University, state and federal regulations limit the **radiation dose** to a member of the general public – including non-radiation workers – to 100 mrem per year from University operations.

In comparison, the average background **radiation dose** to a person living in Pennsylvania is about 360 mrem per year. A typical chest or dental x-ray exam delivers a radiation dose of 10 mrem to the patient.

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http://www.bupa.co.uk/wellness/asp/personal/health_assessmen...

A scan is fast, safe, accurate, painless and non-invasive, taking just 15 minutes to perform. No preparation is required; you don't even need to get undressed. You simply lie on a padded table under the arch of the scanner. Your head is not enclosed at any time so there is no feeling of claustrophobia. You will simply be asked to hold your breath a few times while a series of pictures is taken. The **radiation dose** is equivalent to two to three months of natural background radiation that we are all subject to.

http://en.wikipedia.org/wiki/Background_radiation

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NB: **radiation dose** is also used when speaking of non-ionizing radiation, but it's not very common

http://www.google.com/search?hl=en&q="non-ionizing radiation...

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hth!