ARCHIVE: e-Digest Statistics about: Radioactivity

Natural Sources of Radiation

Cosmic

Cosmic radiation results from the interaction of high energy protons from outer space with the atoms of the upper atmosphere to produce secondary ionising radiation consisting mainly of muons and electrons. At sea level, the average annual dose from cosmic radiation outdoors is about 0.36 mSv. However, since people spend most of their time indoors, the average exposure is estimated to be around 0.3 mSv, because of the partial shielding provided by buildings. Dose rates from cosmic radiation increase sharply with altitude, but this has little effect in the UK since most of the population lives in low lying areas.

Exposure, however, is increased during air travel, and this is estimated to increase the average annual individual dose by 0.02 mSv, resulting in an overall average annual dose of 0.32 mSv from cosmic radiation. This is an increase since the previous study resulting from an almost 50 per cent increase in air travel in the past decade and improvements in measurement. People flying about 100 hours annually would receive a further annual cosmic radiation dose of about 0.4 mSv. Frequent flyers who travel for more than 1,200 hours per year, could receive doses of up to 5 mSv per year. Cosmic rays also produce radionuclides, for example tritium (³H), beryllium-7 (7Be) and carbon-14 (14C) from non-radioactive atoms in the air. These radionuclides can be inhaled, but produce only a low dose.

Further Information:
Key Facts:
Sources
Natural sources: Radon, Gamma, Cosmic, Food and drink
References, further reading and links to other resources:
[1] Hughes, J S, National Radiological Protection Board (1999). Ionising Radiation Exposure of the UK Population: 1999 Review, NRPB-R311. TSO.
Internet Links:
National Radiological Protection Board (NRPB)

Your questions and comments about information presented on this page are welcome. Contact information and Email . Copyright of data and/or information presented or attached in this document may not reside solely with this Department. Please see guidance on Copyright.

Page last modified: 16 September 2003
Page published: 10 September 2003