radiation

Figure 4.3.

Figure 4.3 The average background radiation levels in the UK is 2.6 mSv per year from the sources detailed in this pie chart.

(Courtesy of the National Radiation Protection Board now the Health Protection Agency).

The major sources of natural radiation are the radioactive gases radon and thoron. Together they contribute over 50% of the average background radiation dose in the UK. These gases are generated in granite rock and, as a consequence, the intensity of the radon exposure varies considerably around the world, being higher in areas were there is more granite rock. In addition, if the rock is cracked the gas can escape into the environment more easily leading to higher levels in the environment. Such a situation exists in Cornwall where the level of radon gas is up to three times the national average. This has consequences in terms of the gas entering the homes of people living in these areas. Since the trend is to insulate homes more rigorously, this can have the effect of trapping the gas in the homes, leading to elevated doses to the inhabitants. Constructing well-ventilated houses and incorporating a special membrane into the foundation of new houses can alleviate this. Installing extraction fans and increasing under floor ventilation may improve older properties. These natural sources contribute an average dose of about 2.3 mSv per annum to a member of the UK population.

Another 0.3 mSv per annum is contributed to by artificial or man-made sources, such as discharges from nuclear power stations, making the average total dose 2.6 mSv. However, the biggest contribution is from the diagnostic uses of radiation where, although the individual doses are small, a large number of x-rays are performed with, on average, every member of the UK population undergoing at least one x-ray examination per year. Since this is a controllable exposure to some extent, a great deal of effort has been put into reducing both the individual dose per patient and the number of examinations carried out. This has been brought about by both legislative requirements (see below) and good practice guidelines.

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