Environmental radioactivity in the UK: the airborne geophysical view of dose rate estimates

Abstract

Highlights: UK airborne estimates of dose rates have been obtained across 40,000 km ABSTRACTThis study considers UK airborne gamma-ray data obtained through a series of high spatial resolution, low altitude surveys over the past decade. The ground concentrations of the naturally occurring radionuclides Potassium, Thorium and Uranium are converted to air absorbed dose rates and these are used to assess terrestrial exposure levels from both natural and technologically enhanced sources. The high resolution airborne information is also assessed alongside existing knowledge from soil sampling and ground-based measurements of exposure levels. The surveys have sampled an extensive number of the UK lithological bedrock formations and the statistical information provides examples of low dose rate lithologies (the formations that characterise much of southern England) to the highest sustained values associated with granitic terrains. The maximum dose rates (e.g. > 300 nGy.h -1 ) encountered across the sampled granitic terrains are found to vary by a factor of 2. Excluding granitic terrains, the most spatially extensive dose rates (> 50 nGy.h -1 ) are found in association with the Mercia Mudstone Group (Triassic argillaceous mudstones) of eastern England. Geological associations between high dose rate and high radon values are also noted. Recent studies of the datasets has revealed the extent of source rock (i.e. bedrock) flux attenuation by soil moisture in conjunction with the density and porosity of the temperate latitude soils found in the UK. The presence or absence of soil cover (and associated presence or absence of attenuation) appears to account for a range of localised variations in the exposure levels encountered. The hypothesis is supported by a study of an extensive combined data set of dose rates obtained from soil sampling and by airborne geophysical survey. With no attenuation factors applied, except those intrinsic to the airborne estimates, a bias to high values of between 10 and 15 nGy.h -1 is observed in the soil data. A wide range of technologically enhanced, localised contributions to dose rate values are also apparent in the data sets. Two detailed examples are provided that reveal the detectability of site-scale environmental impacts due to former industrial activities and the high dose values (>500 nGy.h -1) that are associated with former, small-scale Uranium mining operations.

The use of unmanned aerial systems for the mapping of legacy uranium mines

“…Airborne radiation monitoring has previously been conducted over the St Stephen region, with the most recent survey conducted as part of the Tellus South-West project (Beamish, 2014), led by the British Geological Survey (BGS). This survey, conducted in lightweight aircraft with an altitude of 56 to over 200 m at speeds typically between 60 and 70 m s À1 using a 200 m survey line separation identified a radiation anomaly at the South Terra site.…”

Environmental Radiation: Natural Radioactivity Monitoring

“…It has been recognized that there are some places with large inhabitants that encompass high levels of background radiation in environmental compartments. Great interest given worldwide for the study of naturally occurring radionuclides has led to the performance of broad investigations in many countries [3][4][5][6][7][8][9][10]. Investigators attempted to correlate the distributions of natural radionuclides with some settings such as geology, soil characteristics, etc.…”

The Cornubian geothermal province: heat production and flow in SW England: estimates from boreholes and airborne gamma-ray measurements

“…Additional attenuation effects are introduced when the material contains water (Løvborg 1984;Grasty 1997). The additional sensitivity of wet soil was investigated by Beamish (2013Beamish ( , 2014a) who provides a set of exponential decay curves as a function of soil type (e.g. density) and degree of saturation.…”