An Airborne Gamma Ray Survey of Three Ayrshire Districts

<p>An aerial radiometric survey of Cunninghame, Kilmarnock and Loudon and Kyle and Carrick districts was conducted by SURRC from July 16th to 2nd August 1990. A 16 litre NaI spectrometer was used to map the distribution of radiation from 137Cs, 40K, 214Bi, 208Tl, and also to estimate the total gamma dose rate from all sources over an area of 2500 km2. A helicopter, chartered from PLM (Inverness), was used to survey the districts at a height of 100m above ground, flight lines being spaced by approximately 1 km and oriented north-south within the study zone.</p> <p>More than 6000 gamma ray spectra were recorded in the survey. Integrated count rates for each nuclide have been collated and calibrated to ground level area inventories based on a comparison between airborne and terrestrial gamma fluxes over sites of known radioactivity. Extensive field based studies were conducted in parallel with the aerial survey to support the calibration. Detailed colour contour maps show the distribution of radionuclides with roughly 1 km resolution throughout the area.</p> <p>The survey is intended to provide a comprehensive baseline against which any future changes can be measured. In the event of any future nuclear accident it will be possible to state clearly what has been added to the existing background.</p> <p>The variations in natural background sources have been defined and can be related to underlying geological features. Granite masses in the north of Arran and SW of Loch Doon show elevated levels of potassium, 214Bi (denoting post-radon uranium series activity) and 208Tl (from the decay of thorium). By contrast the ultrabasic rocks which occur on the mainland in all three districts show natural radioactivity levels between 5 and 10 times lower. Sandstone areas give intermediate results. 214Bi is a radon daughter product which may be of value in indicating the variation in radon source term underlying domestic problems.</p> <p>137Cs has been mapped in detail. Peak fallout occurs principally in the SE of Kyle and Carrick (> 25 kBq m-2), in parts of central Arran (> 15 kBq m-2), and more generally inland (> 10 kBq m-2). Some coastal areas have been virtually unaffected by Chernobyl. Marine 137Cs was detected notably on salt marshes near to the Irvine racecourse and on the Western coast of Great Cumbrae. Part of this inventory derives probably from Sellafield, and perhaps from Hunterston. Local sampling programmes here would be of interest. Close to the Hunterston “A” power station a small area with over 10 times natural gamma activity was encountered by helicopter. Scottish Nuclear were informed of these findings and conducted a prompt ground level investigation to identify the source of the activity, associated with an obsolete precipitator plant. This source of activity will be removed during decommissioning, and it is suggested that a repeat survey be conducted once this has been done.</p> <p>Despite the presence of readily measurable anthropogenic sources in many parts of the three districts the overall environmental quality appears to be high. Natural sources account for the majority of the measured gamma ray dose rates, and the higher activity rock types apparently occur in sparsely populated zones. Follow up studies to examine further details of these patterns at ground level, and to itigate domestic and urban contexts wouldvaluable. The archival results generated in this projreprese useful resource for such studies, and asecure the possibility of detecting future changes he event of anident involving significant quantities odioactivity.</p&gt