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

OSL investigations at Hardisty, Alberta, Canada: Sections HD03, HD04 & HD05

This report is concerned with optically stimulated luminescence (OSL) investigations of a number of sediment stratigraphies in the Battle River Valley area, near Hardisty, east-central Alberta. Archaeological investigations in this region, led by Rob Wondrasek, have identified thousands of historical artefacts, including projectile points and lithic fragments indicative of occupation. Ken Munyikwa visited the archaeological sites at Hardisty in June 2014 and January 2015 to sample key units within the sediment stratigraphies for OSL dating. The sediments associated with the artefacts were appraised through five profiles, Hardisty-1 (HD01) to Hardisty-5 (HD05), comprised of 43 field-profiling and 14 dating samples. Profiles HD01 and HD02 were sampled in June 2014; and profiles HD03 through to HD05 in January 2015. The dating questions associated with these materials relate to the age of artefact-bearing horizon, through dating the enclosing sediments above and beneath the archaeological soil, it should be possible to provide terminus post quem (TPQ) and terminus ante quem (TAQ) on the age of the artefacts. The conventional quartz SAR OSL approach was examined as a potential method for providing the depositional ages of the sediment enclosing the artefacts. Luminescence profiling during fieldwork had revealed stratigraphically progressive IRSL and OSL signals, indicating sediment with dating potential. Dose rate estimates from these sediments were assessed using a combination of high resolution gamma spectrometry (HRGS) and thick source beta counting (TSBC), reconciled with each other, water contents and modelled micro-dosimetry. Where appropriate, the external gamma dose rates received at the position of the dating sample were reconstructed from the adjacent bulk gamma spectrometry samples, yielding wet gamma dose rates between 0.42 and 0.54 mGy a-1, which are comparable with those recorded at each sampling position. Equivalent doses were determined by OSL from 16-48 aliquots of quartz per sample (depending on quartz yields) using a single-aliquot-regenerative (SAR) approach. The material exhibited good OSL sensitivity and produced acceptable SAR internal quality control performance. Radial plotting methods revealed some heterogeneity in the equivalent dose distributions of each sample, indicating that each sample enclosed mixed-age materials, reflecting variable bleaching at deposition. The field profiles provide some measure of control on this. Luminescence ages were calculated using standard microdosimetric models, with uncertainties that combined measurement and fitting errors from the SAR analysis, all dose rate evaluation uncertainties, and allowance for the calibration uncertainties of the sources and reference materials. The quartz OSL ages reported here for the sand sequences at HD03 to HD05, contribute to the expanding catalogue of chronological data on the depositional sequences at Hardisty, and further, provide the means to assess the temporal and spatial distribution of artefacts across the site. The sediment chronologies established for each profile are internally and mutually coherent, spanning at HD03 from 7.3 ± 0.3 ka (SUTL2778) to 9.0 ± 0.5 ka (SUTL2780), at HD04 from 7.0 ± 0.3 ka (SUTL2781) to 8.3 ± 0.4 ka (SUTL2782), and at HD05 from 8.3 ± 0.5 ka (SUTL2783) to 9.6 ± 0.6 ka (SUTL2785). The field profile at HD05 reveals some complexity to its depositional history, with notable maxima and inversions in intensities from 150cm depth, potentially reflecting reworking and re-deposition of sediment within this sequence. TAQ for this phase of reworking is provided by the youngest unit examined in the profile, which at 7.5 ± 0.6 ka (SUTL2784), is consistent with the occupational phase recorded in the adjacent sections. The sediment chronologies established in this dating campaign, and in the 2014 campaign, are synchronous suggesting contemporaneous deposition across the site, and presumably, with local knowledge, scope for further age modelling including the use of Bayesian methods to refine the TAQ and TPQ age limits

Luminescence dating of ditch fills from the Headland Archaeology Ltd. excavation of Newry Ring Fort, Northern Ireland

This study supports a new investigation into the construction, occupation and utilisation history of a Mediaeval ring fort near Newry, southwest Northern Ireland (section 2). Optically stimulated luminescence (OSL) profiling and age determinations have been made for two sequences of sediments accumulated in the ring ditch surrounding the fort, and potential has been assessed for TL dating of a Souterrain-Ware sherd from a pit feature within the site complex (section 3). The archaeological significance of the age determinations has been reviewed in the light of the luminescence results and the samples’ depositional contexts, to constrain the deposition/formation dates of the sampled sediments (section 6).<p></p> A total of 31 profiling (sections 5.1, 5.2) and 12 age (section 5.5) determinations were made. Profiling measurements were made using simplified equivalent dose determination procedures on polymineral coarse and hydrofluoric etched sand-sized mineral grains (sections 4.2.2). Dose rate determinations were made using thick source beta counting, high-resolution gamma spectrometry, field gamma spectrometry, measured water contents and calculated cosmic dose rates (sections 4.2.1 and 5.3). Equivalent dose determinations were made (sections 4.2.2, 5.4) using the OSL signals from sand sized grains of quartz separated from each sample.<p></p> The luminescence behaviour of the Newry Ringfort samples was generally very good. Profiling indicated variable levels of residual luminescence signal through the sections (sections 5.1, 5.2), but OSL on the etched fraction was found to be least affected, and measurements on fully prepared quartz for dating appeared even less so (sections 6.1, 6.2). Dose rates ranged from 2.6 to 3.9 mGy/a, De values from the dating samples ranged from 0.7 to 5.0 Gy. Estimates of sediment accumulation date ranged from 410AD to 1750AD (section 5.5). Uncertainties on the age estimates were commonly around 3%, but young samples with scattered equivalent dose distributions had estimated age uncertainties of up to 11%.<p></p> The external dose rate to the sherd was estimated to be 1.33 mGy/a ± 0.12 (sections 6.3, 7). Precision was limited by uncertainties in average water content during burial rather than heterogeneity in the gamma radiation field: providing the range of sediment radioactivity at a site can be assessed, and the average burial water contents of sherds excavated from it can be well constrained, then it is likely that sherds from around a site could be dated with sufficient precision to establish a broad chronology for Souterrain-Ware.<p></p> The earliest sediments in the ditch of the ringfort indicated that its construction predates the end of the 6th Century AD (sections 6.4, 7). These and other OSL age estimates indicated continued occupation until the mid 11th Century, or phases of occupation in the 7th, 9th and 11th Centuries. Results from the base of a colluvial soil sealing these layers indicate that the site was set to cultivation at or around the time of the Norman invasion of Ireland (1169AD), rather than in the post Mediaeval period. Abandonment of the ringfort must have occurred at the time of the invasion or in the century before it. Samples from throughout the colluvial soil also indicated that it continued to accumulate until at least the 18th Century, and probably into the 20th Century

Luminescence dating of wind-blown sands from the Broo Peninsula, Shetland

This report provides a temporal framework to support University of Stirling geo-archaeological investigations near Huesbreck, Broo Pennisula (Shetland), examining how the early modern population there, adapted to harsh climate conditions in the 18-19th centuries, when enhanced aeolian activity led to an influx of sand to the area, leading to adaption’s in farming practices, and abandonment of several sites. Five sediment samples were submitted to the luminescence laboratories at SUERC for dating. All samples were subjected to laboratory preparation of sand-sized quartz, and purity checked using scanning electron microscopy. Dose rates for the bulk sediment were evaluated using analyses of the uranium, thorium and potassium concentrations obtained by high resolution gamma spectrometry coupled with beta dose rate measurement using thick source beta counting, and in situ field gamma spectroscopy. Equivalent doses were determined by OSL from 32 aliquots of quartz per sample using the quartz single-aliquot-regenerative (SAR) procedure. The material exhibited good OSL sensitivity and produced acceptable SAR internal quality control performance. Radial plotting methods revealed good internal homogeneity in the dose distributions obtained for each sample. The chronology established for the sampled sands on the site spans from the mid 16th century (AD 1540 ± 40; SUTL2441) through to the early 19th century (AD 1810 ± 25), with the dates falling within three clusters - the waning stages of the Little Ice Age, the mid 18th century (AD 1730 ± 25 to 1760 ± 25) and the early 19th century (AD 1810 ± 25). In the wider region, periods of sand movement and deposition in the mid 18th century, and early to late 18th century, are documented in sediment statigraphies sectioned at the Old Scatness Broch, Scatness

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