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Home Topics Radiation Understanding Radiation Understanding Radiation - Topics Dose comparisons for ionising radiation

Dose comparisons for ionising radiation

Every day all over the world people are exposed to ionising radiation, almost all from natural sources in the environment or for medical reasons. 

Ionising radiation has enough energy to cause damage cells which can increase the risk of cancer later in life. However these risks to health are actually low and ionising radiation is widely used in cancer therapy. In general the health effects of ionising radiation are dependent on the dose received. While low doses increase the risk of cancer later in life, very high doses act like a poison and can be fatal.

In the UK the HPA has calculated that on average people are exposed to about 2.7 millisieverts (mSv) of radiation a year. A millisievert is a measure of radiation dose which accounts for the fact that ionising radiation can affect different parts of the body to differing degrees. The millisievert dose also allows for the different effects of different types of radiation, x rays, gamma rays, neutrons, alpha particles and beta particles.

The 2.7 mSv dose that people in the UK are exposed to comes from a number of sources. Many building materials contain low degrees of natural radioactivity and radon gas seeps from the ground into all buildings, so the largest exposure is to naturally occurring radiation in homes and workplaces. There are also significant contributions from naturally occurring radioactivity in food and from medical exposures.

Comparison of doses from sources of exposure


Source of Exposure


Dental X-ray

0.005 mSv

135g bag of Brazil nuts

0.005 mSv 

Chest X-ray

0.02 mSv

Transatlantic flight

0.07 mSv

Nuclear power station worker average annual occupational exposure

0.18 mSv

UK annual average radon dose

1.3 mSv

CT scan of the head

1.4 mSv

UK average annual radiation dose

2.7 mSv

USA average annual radiation dose

6.2 mSv

CT scan of the chest

6.6 mSv

Average annual radon dose to people in Cornwall

7.8 mSv

Whole body CT scan

10 mSv

Annual exposure limit for nuclear industry employees

20 mSv

Level at which changes in blood cells can be readily observed

100 mSv

Acute radiation effects including nausea and a reduction in white blood cell count

1000 mSv

Dose of radiation which would kill about half of those receiving it in a month

5000 mSv