Following the Chernobyl reactor accident in 1986, RIMNET, the nuclear radiation monitoring and nuclear emergency response system, was installed in 1988 to monitor the consequences for the UK of nuclear incidents abroad. The system is now utilised in the UK response to all major radiological events.
Radiation dose rate readings (gamma plus cosmic) from 96 sites around the UK are collected every hour and checked for any indication of abnormal increase. Any readings of radiological significance for the UK would result in an alert being raised and investigated.
Background radiation continues to be the main component of observed levels of gamma radiation recorded at RIMNET sites. The observed UK annual radiation dose rate ranges from around 0.5 mSv to 1.0 mSv with an average of less than 0.7mSv.
The main factor influencing the observed radiation dose rate is the geology of the site. Higher levels are found in areas of igneous rocks, which have relatively high uranium and thorium contents, whilst lower levels are typical of clay and chalk areas. The pattern can be influenced by height above sea level for the cosmic component and climatic effects, for example heavy rain, can cause increased levels of gamma dose rate owing to the wash-out of radioactive daughter products from the decay of naturally occurring radon.
Quarterly monitoring statistics published in Microsoft Excel are published. Separate results are also provided for mobile monitors also measuring gamma dose rate.
Previous returns are available from The National Archive.