Report on Airborne Radiometric Survey of the Thurso Area, 15th to 17th November 2006

Sanderson, D.C.W. and Cresswell, A.J. (2007) Report on Airborne Radiometric Survey of the Thurso Area, 15th to 17th November 2006. Scottish Universities Environmental Research Centre.

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A survey of part of Caithness near Thurso has been conducted as a performance test for a new Airborne Gamma Spectrometry (AGS) system developed at SUERC. The system deployed for this work consisted of a 16 litre NaI(Tl) spectrometer using a 2s measurement time. A total of 7500 spectra were collected in 13.5 hours flight time between the 15th-17th November 2006. The survey comprised a 60x31km area with a 5km line spacing providing an overview of the regional radiation environment, and a 15x20km area at 250m and 500m line spacings providing detailed information on the radiation environment of the Forss Water and River Thurso and their catchments. The survey areas did not include the Dounreay site and the town of Thurso. The data were processed to estimate activity concentrations of 137Cs (kBq m-2), naturally occurring 40K, 214Bi and 208Tl (Bq kg-1) and the gamma ray dose rate (mGy a-1). Maps were produced for the distribution of these activities within both the larger and more detailed survey areas. The gamma dose rate is driven by the natural activity, with no significant contribution from 137Cs activity. The region has considerable areas of saturated peat, suppressing the radiation from the underlying geology. The demarcation between the peat and the flagstone formations with thin soil overlays is clearly seen in the natural series activity and dose rate maps. 137Cs activities of up to 10 kBq m-2 have been observed on the drier land, consistent with Chernobyl fallout, with strongly suppressed signals from the peaty areas indicating that any fallout on these areas has migrated down through the peat. This work confirms the presence of features which accumulate 137Cs in the Forss Water system that had been noted in the survey commissioned by UKAEA in 1998. One feature observed in 1998 is absent in the data recorded in this work. Additional features were also recorded for the first time in the Forss Water upstream of the 1998 survey, and a series of similar featured, potentially of more limited extent, in the River Thurso system. The exploratory survey to the west also showed possible small scale features in Strath Halladale. Additional work would be needed to assess the dynamics of these systems, and their detailed local spatial characteristics and activity profiles, and to explore the extent to which similar features can be found in the fluvial catchments of other areas subjected to radioactive fallout in upper catchments, particularly those with peaty substrates. Time series analysis of these new data in comparison with older airborne data sets from the region would be of value, as would additional work in the future to extend the spatial and temporal boundaries of this survey.

Item Type:Books
Glasgow Author(s) Enlighten ID:Sanderson, Professor David and Cresswell, Dr Alan
Authors: Sanderson, D.C.W., and Cresswell, A.J.
Subjects:G Geography. Anthropology. Recreation > GE Environmental Sciences
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Publisher:Scottish Universities Environmental Research Centre
Copyright Holders:Copyright © 2007 Scottish Universities Environmental Research Centre
First Published:First published as Report on Airborne Radiometric Survey of the Thurso Area, 15th to 17th November 2006
Publisher Policy:Reproduced with the permission of the authors

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