The effect and measurement of naturally occurring radionuclides in the Grampian region
The project has been concerned with the study of radon and other natural radionuclides in the U-238 decay series in the environment. The contribution made by radon and its daughter radionuclides to population radiation dose both in the air and in water supplies has been investigated. The natural radioactivity of the river water, stream water, sediments and freshwater mussels have been measured using a thick source alpha counting technique and γ-spectrometry (water samples were preconcentrated by manganese dioxide precipitation method). The ^226Ra activity ranged from 10-20 Bq m^-3 in the river and 4-30 Bq m^-3 in stream water. The highest values were found close to the source of the river where the water flowed through an area of igneous rocks. Such granite type rocks are enriched in uranium and thorium. Concentrations of radon and its daughters were measured, indoors and outdoors, using a grab sample technique. Outdoor concentrations were 10-30 Bq m^-3 depending on underlying rocks, meteorological condition (pressure, temperature, snow, rain), while indoor values ranged between 20 and 600 Bq m^-3 depending on radon input rate (source strength, ventilation rate and pressure inside the building). The relationship between the indoor ^222Rn concentration and ventilation rate was investigated. The radiation dose and the consequent risk due to inhalation of radon and its daughters were estimated. The annual effective dose equivalent ranged from 0.12 to 11 mSv. The radon concentrations in well waters were measured and were found to range between 3 and 76 Bq ℓ-1. This variation can be associated with different bedrock. A model predicting average indoor increments due to this source is presented and supported by a series of measurements made in the houses which were supplied by well water. The maximum annual effective dose equivalent from inhalation and ingestion was found to be 0.27 and 0.054 mSv respectively.