Revise: Nuclear radiationDose limits

In everyday life, everyone will receive doses of radiation. This could be from natural or artificial sources.

Background radiation is all around us. Some of it comes from natural sources and some comes from artificial sources.

Natural sources

Natural sources of background radiation include:

• cosmic rays - radiation that reaches the Earth from space
• radon gas - this radioactive gas is given off by tiny amounts of uranium that occurs in rocks and soil
• rocks and building materials - rock, stone and building materials like concrete, bricks and ceramics all emit radiation
• food and drink - plants absorb radioactive materials from the soil and these pass up the food chain
• water
• air

For most people, natural sources contribute the most to their background radiation dose. The dose will vary depending on several factors including:

• geology of local area
• altitude
• latitude

There is little we can do about natural background radiation. After all, we cannot stop eating, drinking or breathing to avoid it.

Artificial sources

Human activity has added to background radiation by creating and using artificial sources of radiation. These include:

• medical and dental X-rays
• radiation used in medical diagnosis and treatment (eg radiotherapy to treat cancers)
• rdioactive fallout from nuclear weapons testing
• radioactive waste from nuclear power stations
• industrial and consumer use of radiation (eg smoke detectors, UV sterilisation equipment, indutrial measurement equipment)

Artificial sources account for about 15 per cent of the average background radiation dose. Nearly all artificial background radiation comes from medical procedures, such as receiving X-rays for X-ray photographs.

Equivalent and effective dose

Some occupations will increase your dose as you will work in an environment where you may be exposed to more, but still very small doses. For example, aircraft crews, radiation workers and miners may all have increased doses.

The average equivalent dose for a member of the public (due to background radiation) in the UK is 2.2mSv.

In addition, depending upon your occupation, the annual dose limit for a member of the public is 1mSv.

This is referred to as an “effective” dose and is a measure of the impact an occasional radioactive material may have on you.

For someone working in the radiation industry (power stations, hospital, and research purposes) the annual effective dose limit they may receive is 20mSv.