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

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

Mobile gamma Spectrometry Measurements of Coneyside Beach, Cumbria

<p>Environmental radioactivity arises from natural and anthropogenic sources: 238U, 232Th and their decay products, and 40K in differing concentrations in rocks and soils; natural materials transformed by industrial processes to enhance the concentrations of some radioactive isotopes; materials discharged from some nuclear processes; fallout from nuclear accidents and weapons testing; radioactive sources that may have been lost or stolen; and radiation shine from sites using nuclear technology. Mobile gamma spectrometry provides powerful methods of measuring the distribution of radioactivity in the environment; airborne platforms allow the rapid survey of large areas, and ground based platforms more detailed surveys of smaller areas.</p> <p>Airborne surveys in 1990 (conducted to produce a baseline data set for the Sellafield site) and 2000 (as part of a large study on spatial and temporal aspects of airborne measurements) showed several radiometric features along the coast, including elevated 137Cs activity along a beach in West Cumbria between St Bees and Nethertown, in an environment comprising pebbles and gravel where this was unexpected. An additional short survey of this area was conducted during the 2000 survey, at reduced ground clearance and speed, to verify the existence of these unexpected signals. With increased interest in the search and recovery of particulate activity from the beaches in the vicinity of Sellafield, this data was reviewed in 2008 to illustrate the use of airborne methods in locating potential particulate activity on beaches and to aid in the planning of further ground based investigations. SUERC conducted an exploratory ground based survey in June 2010; to investigate whether the features observed in the airborne surveys were still present, to define the spatial distribution of activity more precisely, and to attempt to assess the form of the activity and whether it had been redistributed since 2000. This report presents the 2000 airborne measurements reviewed in 2008, with the results of the June 2010 survey.</p> <p>A portable gamma spectrometry system has been developed at SUERC. This consists of a 3x3” NaI(Tl) detector with digital spectrometer, a GPS receiver and netbook computer. The system is lightweight, easy to use and can be carried over terrain that would be inaccessible to vehicular systems. By holding the detector close to the ground the extent of any observed enhanced activity feature can be determined more precisely. Two of these systems have been field tested on the 22-23rd June 2010 along this beach.</p> <p>The exploratory survey has clearly demonstrated the utility of the SUERC backpack system in producing detailed maps of the distribution of radioactive materials in the environment. A survey using two systems successfully mapped an area of approximately 50x200m with very high density measurements in a period of approximately 2h.</p> <p>It has shown that the enhanced 137Cs activity is still present on the beach, in locations that are consistent with the earlier airborne measurements. The more detailed survey shows a pattern of patches of enhanced 137Cs activity. Samples collected from some of these had concentrations of 50 Bq kg-1, which would account for the observed 137Cs count rate. The nature of the material that carries this activity is at present unknown.</p&gt

Luminescence dating of sediments from two sites near Anuradhapura, Sri Lanka

Previous Optical Stimulated Luminescence (OSL) investigations of irrigation features and archaeological sites in the hinterland around Anuradhapura, Sri Lanka, had observed highly heterogeneous dose distributions and apparent ages older than expected for bunds and similar constructions. These observations are consistent with utilising older sedimentary materials, which did not have their luminescence signals reset during construction. The work reported here consists of OSL measurements from two sites in the Anuradhapura region. The first is a modern bund, sampled to examine the degree of heterogeneity of the dose distributions from a control structure. Two samples were taken from within this bund, one near the top and the other just above the land surface the bund was built upon. These show dose distributions that are highly heterogeneous with apparent ages in excess of 1500 years. The third sample from this site is from the truncated land surface beneath the bund, and gives a luminescence age of 150 ± 40 years with just one much older aliquot. The second site in this work is an abandoned red-earth platform site, covered by an extensive layer of cultural deposits. A sample from the overlying deposits just above the constructed platform gives a luminescence age of 540 ± 70 years, with a homogenous dose distribution. A sample from near the top of the constructed platform gives a heterogeneous dose distribution and apparent ages up to 4000 years. The results support the inferences from earlier sampling, providing clear confirmation that platform sites contain unbleached, re-deposited sediments, with significant residual OSL ages. The OSL results from the underlying land surfaces, and from slowly accumulated abandonment layers, appear to be consistent with external age control where available and thus are to be preferred as targets for OSL dating in such geo-archaeological investigations

Exploratory Single Grain OSL Analysis of Sediments from Capu di Locu, Corsica

Single grain optically stimulated luminescence (OSL) measurements have been conducted on retained material from sediment samples collected during excavations of Neolithic monuments at Capu di Locu, Belvédère, SW Corsica. One sample was taken from a presumed burial chamber at Tola and two from the lower fill of the construction pit of a menhir at Stantare. Analysis was conducted on 150-250 µm quartz grains previously separated for single aliquot regeneration (SAR) measurements, and on 250-500 µm grains prepared for this analysis. Single grain measurements, including analysis of blank discs prior to dispensing mineral grains, were conducting on a Risø DA-20 automatic reader, with 800-1000 grains measured for each of two samples, and approximately 350 grains for the third sample. These exploratory measurements have demonstrated that a relatively large proportion (>20%) of mineral grains produce significant OSL counts for both the natural stored dose and following a 25 Gy artificial dose. Previous analysis of these samples using multi-grain aliquots measured using a single aliquot regeneration (SAR) protocol had shown broad dose distributions, with mixtures of aliquots of different ages. The single grain measurements have confirmed that these are mixed age deposits. Two samples show stored dose distributions around mean values which correspond to archaeological ages, for the third the stored dose distribution is significantly broader with no apparent archaeological age component. Further statistical analysis of these data would be required to attempt to resolve archaeological age material, that could potentially be used to further constrain construction dates for these monuments. It is expected that similar luminescence properties would be exhibited by mineral grains from other samples collected during the excavations of these sites, and it is possible that further single grain OSL analysis of other parts of the site may produce dose distributions with less mixing and more readily resolved components with archaeological ages. Meanwhile SG apparent ages were obtained from the Tola sample which are consistent with previous estimates, and two new estimates have been achieved from the Stantare site which indicate potential for recovering archaeological ages in the 3rd to 4th millennium BC from the Menhir site

Operator related attenuation effects in radiometric surveys

Radiometric surveys using airborne, vehicular mounted or backpack detector systems are increasingly used to identify and evaluate complex distributions of radioactivity in the environment. The signals detected depend on the energy and spatial distribution of radioactive sources, the material properties of the environment and the specific properties of the detector systems employed. Materials in close vicinity to the detector such as housings, and intermediate materials may have a critical impact on detection efficiency, and must therefore be taken into account in calibration. This study evaluates the effect of shielding by the body of the operator in backpack surveys. Controlled experiments using point sources and absorbers, chosen to represent the form and composition of human tissue, were conducted, and coupled to an analytical radiation transport model to estimate attenuation factors for mapping of 137Cs. In this way generic factors to correct for this effect using portable spectrometers have been determined. The results compare well with observations at sampled calibration sites in Fukushima and the Solway area in Scotland. Reductions of the 137Cs full-energy peak intensity between 20% and 30% may be expected depending on operator stature and the offset position of backpack systems. Similar effects may be present for other radiometric systems carried by a human operator