14,936 research outputs found
Experimental Measurements and Computer Simulation of Fission Product Gamma-Ray Spectra
No full textAirborne gamma ray spectrometry using high volume scintillation detectors, optionally in conjunction with Ge detectors, has potential for making rapid environmental measurements in response to nuclear accidents. An experimental investigation and computer simulation have been used to characterise the response of such detectors to short lived fission products. Small samples of 235U were irradiated in a research reactor for short periods, to generate fission product sources. Gamma ray spectra were recorded over a period of one year using both high volume scintillation detectors and semiconductor detectors. The main gamma emitting nuclides have been identified, and their associated signals in each detector defined. Simulation work has been used to calculate the corresponding spectra which would have been observed at airborne survey heights, or from fission product sources irradiated for a prolonged period. While Ge detectors can record a fuller range of isotopes, of interest in characterising release terms, the NaI spectra also have potential for providing data on a range of radiologically important isotopes at all stages
An Aerial Gamma Ray Survey of the Surrounding Area of Sizewell Nuclear Power Station
No full text<p>An airborne gamma ray survey of the surroundings of the Sizewell nuclear power station was conducted to define the present levels of radiation background for reference purposes. A twin engine helicopter fitted with a high volume NaI detector and two semiconductor detectors was used. A 20x30km area around the site was surveyed with 500 m line spacing, with an inner zone of 6x6 km being investigated with 250 m line spacing.</p>
<p>More than 10,000 gamma ray spectra were recorded between 1st and 3rd October 1996 at a survey height of 200-300 feet above ground level and used to prepare maps showing the distribution of 137Cs, 40K,214Bi,208Tl and gamma ray dose rate. The data set has been retained digitally in an archive which can be used in the future should the need arise to measure change resulting from long term site operations, or for emergency response.</p>
<p>137Cs levels are typically around 2 kBq m-2, derived mainly from weapons' testing fallout, with slight Chernobyl input. Peak levels of some 6 kBq m-2 around the tidal inundation limits of estuarine and marsh areas may be associated with marine discharges from nuclear fuel reprocessing at Sellafield. Natural radionuclides show a distribution which reflects the geological and geomorphological variations within the landscape, and are the major contributors to dose rates within the survey zone. The gamma ray dose rate maps also show the position of the 41Ar plume emitted from the Magnox station at Sizewell during the survey. At the time in question the plume was projected over the sea in the SE direction. The gamma ray survey data crossing the plume show clear evidence of dispersion downwind with plume broadening as a result of gaseous diffusion with increasing distance. Ground level gamma ray dose rates were recorded at 8 routine district monitoring sites using a mini-series 680 survey meter operated by Sizewell staff and a portable scintillation spectrometer. The mean dose rates recorded with the 680 meter (24.7 nGy hr-1) are in good agreement with the results of ground based (27.4 nGy hr-1) and the nearest airborne gamma dose rate results (24.6 nGy hr-1).</p>
<p>Airborne survey methods are uniquely well suited to rapid environmental data capture from large areas. This has important emergency response potential which is increasingly recognised in the context of nuclear sites. The data recorded in this study provide a frame of reference against which future changes can be measured.</p>
Review of Past Nuclear Accidents: Source Terms and Recorded Gamma-Ray Spectra
No full textAirborne gamma ray spectrometry using high volume scintillation detectors, optionally in conjunction with Ge detectors, has potential for making rapid environmental measurements in response to nuclear accidents. A literature search on past nuclear accidents has been conducted to define the source terms which have been experienced so far. Selected gamma ray spectra recorded after past accidents have also been collated to examine the complexity of observed behaviour
An Aerial Gamma Ray Survey of Torness Nuclear Power Station on 27-30 March 1994
No full text<p>An aerial gamma-ray survey of the environment of Torness Nuclear Power Station was commissioned by Scottish Nuclear Limited, and conducted by the Scottish Universities Research and Reactor Centre. The area surveyed encloses a 31km square, with Torness Nuclear Power Station at the centre, flown with a line spacing of 500m. A secondary area, in closer proximity to the nuclear site, was flown with 250m spacing.</p>
<p>Over 6000 gamma ray spectra were recorded with a high volume spectrometer operated from a helicopter over a three day period in March 1994. Spectral data were recorded together with satellite navigation (GPS) and radar altimetry data. The results provide a comprehensive record of the radiation environment around Torness and have been used to map the distribution of natural and man-made radionuclides, forming a baseline to enable future environmental changes may be assessed.</p>
<p>The natural radionuclides 40K, 214Bi and 208Tl are highly correlated with each other and show a distribution which reflects both the underlying geological and geomorphological features of the area. The main structural boundaries of the Dunbar-Gifford and Lammermuir faults can be partly discerned in the maps, as can some igneous intrusions. Areas with peat or alluvium cover appear as negative features in the radiometric maps.</p>
<p>Radiocaesium 137Cs levels range from below 4 kBq m-2 to over 20 kBq m-2. Upland areas near Coldingham Common, Black Castle Hill and Dunbar Common show the highest values, similar in deposition pattern and level to Chernobyl activity observed in the West of Scotland and elsewhere. Published national maps derived from meteorological and ground sampling data predicted much lower levels for these locations. However core samples taken after the survey have confirmed the presence of the activity, and the attribution to Chernobyl. This finding demonstrates both the effectiveness of the method for rapid location of radioactive deposition, and the need for baseline studies to determine present levels. Count rates from a spectral window corresponding to 60Co were also mapped. The results are close to detection limits and show a slight correlation with natural sources. Therefore they are more probably due to residuals remaining after separation of spectral interferences than to low level 60Co contamination.</p>
<p>Gamma ray dose rates range from approximately 0.1 to 0.6 mGy a-1 with a mean value of 0.34 mGy a-1, and are derived mainly from natural sources. Ground level measurements were taken at nine district monitoring points within the area using a 3x3" NaI spectrometer and a survey meter (Series 6/80) used routinely by SNL. Both ground based data sets were in good agreement with each other and with the aerial survey after accounting for instrumental and cosmic ray background contributions.</p>
<p>There is no evidence that Torness Power Station has affected the surrounding radiation environment, within the operational and sensitivity limits of the aerial survey.</p>
<p>The longer term impact of the site can be assessed by future surveys. Moreover under emergency conditions it would be possible to utilise this method for rapid mapping of the area on a timescale which cannot be matched using alternative approaches. </p>
An Aerial Gamma Ray Survey of Springfields and the Ribble Estuary in September 1992
No full text<p>A short aerial gamma ray survey was conducted in the vicinity of the Springfields site and Ribble Estuary from 1st-5th September 1992, to define existing background radiation levels, against which any future changes can be assessed. A twin engine AS 355 "Squirrel" helicopter chartered from Dollar Helicopters was used for this work. It was loaded with a 16 litre NaI(Tl) gamma ray detector and spectroscopy system on the 31st August and during the following days over 2700 separate spectra were recorded within a survey area of 20 x 12 km. Gamma ray spectra were recorded every 5 seconds at survey speed and altitude of 120 kph and 75 m respectively. A flight line spacing of 0.3km was chosen for the main survey area. On the 3rd September a low altitude, high spatial resolution (flight line spacing 100m and altitude 30m) was made over Banks Marsh (an area frequented by local wild fowlers).</p>
<p>Survey results have been stored archivally and used to map the naturally occurring radionuclides 40K, 214Bi and 208Tl together with 137Cs and total gamma ray flux. In addition, for the first time, estimates of 234mPa in terms of deconvoluted count rate (normalised to 100m altitude) were made in the presence of 228Ac interference probably in disequilibrium with its parent thorium series.</p>
<p>The maps provide a clear indication of the distribution and sources of environmental radioactivity in the Ribble at the time of the survey. The Ribble estuary is subject to regular and ongoing ground based studies by BNF, MAFF, HMIP, and University based groups, as a result of the authorised discharges of low level radioactivity from the Springfields site. The results of this survey complement this ground based work, and add to confidence that the estuarine system, it's associated sediments, tide washed pastures, salt marshes and river banks, have been thoroughly examined. There is support for earlier conclusions that the Cs on the salt marshes is the dominant source of external gamma exposure, and that the Springfields contribution to these locations is minor in comparison with this, Sellafield derived, signal. Upstream the situation is more complex, particularly where the dynamic sources of beta radiation are considered. As far as critical group assessments are concerned the survey provides clear evidence that the areas affected by 137Cs, where external gamma dose and possible food chain effects are of greatest interest, are in the lower reaches of the Ribble, whereas, at the time of the survey the 234mPa distribution was in the upper reaches of the river. This not only confirms the findings of ground based work, but provides some assurance that the different exposure paths (external gamma dose, skin dose) are not entirely synergistic. The discovery of possible transient sources of natural 228Ac in the salt marsh environment as a consequence of Th series disequilibrium immediately following spring tides is extremely interesting. If substantiated by further studies using semiconductor detectors this provides a new insight into the dynamic radiation environment of tide washed contexts.</p>
<p>Aerial survey can potentially provide a rapid and cost effective means of studying environmentally dynamic sources such as 234mPa. In the case of the Ribble it would be necessary to reduce survey height to below 50m ground clearance to improve spatial resolution. Possible inconvenience to residents and property owners of such low altitude flights would have to be considered in addition to the potential value of environmental knowledge of the behaviour of short lived nuclides in a dynamic system such the Ribble estuary. There is nonetheless considerable potential for time series studies of this location.
Recent flight trials by SURRC incorporating high efficiency germanium semiconductor detectors have verified the feasibility and potential a hybrid scintillation⁄ semiconductor spectrometer. Such a device can resolve any ambiguities arising from overlapping gamma ray peaks. This is particularly relevant to the confirmation of 228Ac in salt marshes. Ground based sampling at the time of measurement would enable concentration calibrations to be made for these dynamic sources. Further ground based measurements would be desirable to establish the extent to which low energy photons contribute to external gamma ray dose rates from sources with pronounced subsurface activity maxima.</p>
An Aerial Gamma Ray Survey of Chapelcross and its Surroundings in February 1992
No full textA short aerial gamma ray survey was conducted in the vicinity of the Chapelcross site from 4th-7th February 1992 to define existing background radiation levels, against which any future changes can be assessed. A twin engine AS 355 "Squirrel" helicopter chartered from Dollar Helicopters was used for this work. It was loaded with a 16 litre NaI gamma spectrometry system at SURRC in East Kilbride on the afternoon of 3rd February and flown to an off-site operational base at Lockerbie that evening. Over the following four days over 3500 gamma ray spectra were recorded from a main survey area of 21 x 25 km surrounding the site, and from a extension examining coastal zones up to 25 km further west. Additional NS and EW "tie lines" out to 40 km from the site were added for the purpose of future extendability.
The main survey grid, bounded by OS coordinates NY100590, NY 100800, NY 350800 and NY 350590, was surveyed in a series EW flight lines spaced apart by 500m. Survey speed and height were 120 kilometres per hour and 75 m. respectively. Gamma ray spectra were recorded every 10 seconds, interleaved with positional information collected on-line from a GPS satellite navigation system and time averaged radioaltimetry signals. 3500 spectra were recorded. The combination of line spacing and flight conditions results in a practically complete area survey with 500m spatial resolution. The same flight parameters were adopted for the western coastal extension and the tie lines. Data were recorded in continuous flight tracks through these to minimise flight times.
In addition a rapid response flight route was prepared which could be used to define arcs at 10km, 5km and 2km radii from Chapelcross in the event of a future incident. The path has been chosen to be navigable under most weather conditions, and falls within the area which has been mapped for baseline purposes. A survey aircraft arriving from East Kilbride could perform such a survey without pausing to refuel.
Survey results have been stored archivally and used to map the naturally occurring nuclides 40K, 214Bi, 208Tl together with 137Cs and total gamma ray flux. In interpreting the maps correctly the spatial averaging of the aerial measurements and the contouring process should be taken into account. This leads to a slight tendency to broaden spatial features and to reduce maximum values particularly for boundaries less than the spatial resolution (500m) of the survey. Small scale features will be underestimated. Radiation from the Chapelcross plant was readily detected at the perimeter and can be clearly seen in the gamma dose rate and 137Cs maps. In the former case direct radiation from 16N in the reactor heat exchangers and the release of 41Ar gas from the reactors is largely responsible. The 137Cs associated with the small-bore pipeline on-site was detected to the SW of the reactors. Signals from 234mPa were detected to the NE of the site, and are due to the on-site depleted uranium store in this area. These local observations are broadly consistent with expectations based on-site dosimetry measurements. Further afield the contamination of the Solway Firth, its intertidal sediments and adjacent tide washed pastures by 137Cs is readily detectable, and the distribution visible on the radiometric maps. This is attributed for the most part to past marine discharges from Sellafield. The most extensively affected areas were near Kirconnel in the Nith, at Caerlaverock, Rockcliffe and Burgh marshes. Smaller areas of local enhancement occur close to the tidal limits of most rivers, notably the Southwick burn, Kirkbean Glen, Burnfoot, the river Annan, the Kirtle Water and river Sark. Terrestrial levels of 137Cs vary from those associated with weapons testing fallout (2-4 kBq m-2) which occur in the main survey area, and the edge of the area contaminated from the Chernobyl accident where levels above 10 kBq m-2 are observed in the western extremities of this survey. Previous SURRC surveys have shown that this component is up to 3-4 times higher further to the West.
The natural radionuclides (40K, 214Bi, 208Tl) show variations which reflect the local subsoil geology and surface geomorphology. Prominent features include the eastern edge of the Criffel pluton, Triassic shales are responsible for enhanced levels to the east of the Nith Valley, adjacent negative anomalies are associated with Silurian outcrops to the NE of the Lochar water. Carboniferous limestones and permian sandstones are responsible for the majority of the main survey grid. Natural sources in this survey zone define a relatively low natural background level, against which local signals close to the reactor site and deposited activity on tide washed pastures produce distinct enhancements. Radiation levels at Chapelcross site fall off rapidly with distance from the perimeter, approaching natural levels within approximately 0.5-1 km at the time of the survey. Those from the marine, estuarine and tide washed environments are mostly attributed to past Sellafield discharges. Further ground based investigation of these features would be desirable
An Airborne Gamma Ray Survey of Parts of SW Scotland in February 1993. Final Report
No full textAn airborne gamma ray survey was conducted for the Scottish Office Environment Department of coastal and inland parts of SW Scotland to define existing background levels, to locate features worthy of further attention, and to demonstrate the emergency response capabilities of radiometric methods. Coastal areas were surveyed with 500 m line spacing. Inland areas were specified to 2 km line spacing, however it was possible to achieve 1 km line spacing in the majority of the inland zone.
Fieldwork was conducted between the 1st and 16th February 1993. A total of over 17,000 gamma ray spectra were recorded, using a 16 litre NaI spectrometer mounted in a helicopter flying at 50-75m ground clearance and 120kph. A total area of 3650 km2 was surveyed in 41.6 flying hours, from roughly 4370 line kilometres. The data were reduced in the field using standard SURRC procedures for background subtraction, stripping of spectral interferences, altitude correction, and calibration. Preliminary maps of the distribution of 137Cs, 40K, 214Bi, 208Tl, and estimated ground level gamma dose rate were produced during the fieldwork period using working calibration values derived from previous surveys. A set of core samples was collected from Wigtown Merse, Longbridgemuir and Caerlaverock merse for calibration purposes, and aerial observations were performed at these sites.
Further soil sampling and ground level in-situ gamma spectrometry was performed in the summer of 1993 to investigate the applicability of the calibration to a range of upland soil types and topographical environments. These locations received peak deposition from the Chernobyl accident, are vulnerable to wet deposition, and are difficult to monitor rapidly using ground based methods. A total of 76 soil cores, subdivided into 168 separate samples was thus collected for high resolution gamma spectrometry in the laboratory. This was conducted from April to November 1993.
For the terrestrial sites the aerial survey estimates based on the working calibration, were in good agreement with both in-situ gamma spectrometry and the results of core analysis. This validates the preliminary maps in these contexts, and confirms that a general calibration is sufficient for fallout mapping under emergency response conditions. On coastal salt marsh sites (merse), where aged deposits of Sellafield derived activity have accumulated, subsurface activity profiles for 137Cs and 241Am and the presence of superficial levels of 134Cs were observed from the soil cores. Similar features have been observed in previous surveys. In these cases the effects of source burial must be taken into account to avoid underestimation of activity levels by both ground-based and aerial gamma spectrometry. A separate set of detailed maps for the principal merse sites was therefore prepared using a calibration factor derived from the soil cores from this context. There are prospects for developing spectral analysis procedures to account for source depth in aerial surveys. Source burial on the merse also has implications for sampling techniques, and for dose rate measurement, which would merit further consideration.
The radiometric maps show clearly the distributions of each individual nuclide and indicate the contribution which individual localised features make to the overall gamma ray dose rate. Naturally occurring nuclides reflect the underlying geological and geomorphological contexts of the landscape. The main granite intrusions, most notably at Cairnsmore of Fleet, the Loch Doon Granodiorite, Glencairn of Carsphairn, the Dalbeattie granite, and Criffel Pluton are readily visible in 40K, 214Bi and 208Tl maps, and control their local radiation environments. A number of areas of enhanced 214Bi, which may reflect radon potential, were noted. A transient radon associated 214Bi signal was observed on the west of the Wigtown peninsular during the survey. Examination of spectral data in the vicinity of Dundrennan has confirmed that there is no evidence of widespread terrestrial contamination arising from the use of depleted uranium projectiles on the range.
The 137Cs map indicates the environmental distribution of this nuclide in considerable detail. Levels of 137Cs range from approximately 2 kBq m-2, a level consistent with global weapons’ testing fallout, from 2-40kBq m-2 on terrestrial sites affected by deposition from the Chernobyl accident, and from 40 kBq m-2 to over 200 kBq m-2 on tide washed pastures which have accumulated marine sediments from the Irish Sea. All three levels are represented within the survey zone, in a manner which is consistent with the findings of previous aerial surveys in adjacent areas, and with ground based studies.
The main Chernobyl deposition in Dumfries and Galloway appears to have occurred between an area just east of the Nith, and Glenluce. The northern limit has not yet been defined, and there may be grounds for considering extension of the northern and particularly eastern limits of the inland survey zone. Within the survey zone the deposition pattern is complex, including both upland and lowland components. The plume trajectories for deposition inferred from these observations are oriented northwards rather than in the NW directions predicted by meteorological derived estimates. This may explain the contradiction between results from the Central Highlands and the estimated fallout patterns. The data presented here both add to previous knowledge, and serve as a baseline against which any future changes can be measured.
The survey provides systematic coverage of the sedimentary and terrestrial coastal system for the first time, and has identified a number of merse sites which have accumulated radioactivity from past marine discharges from Sellafield, and which are not routinely monitored under existing Scottish Office arrangements. Some of these locations are extensive and fall within SSI’s; furthermore they are key sites for studying future deposition trends. It would seem prudent to review radiological assessments in the light of this work to ensure that the patterns of occupancy and sensitive ecologies of the merse are taken fully into account.
The emergency response potential of aerial radiometrics has been clearly demonstrated in this project. It provides the only practical means of providing comprehensive environmental measurements of remote and upland landscapes on a short time scale, with an effective area sampling density some 106-107 times greater than soil sampling. Results are compatible with ground based approaches, and could focus ground based efforts effectively under emergency conditions. Modern approaches to data recording and analysis are able to produce maps during the survey period. National baseline mapping in Scotland, at 1 km resolution, would require less than 800 flying hours; 20 km line spacing would take roughly 40 hours of flight time. A long term programme of high resolution national baseline mapping, coupled to an emergency response standby arrangement, would provide an extremely cost effective way of preserving the capability developed since the Chernobyl accident, while producing high quality environmental data for research purpos
An Airborne and Vehicular Gamma Survey of Greenham Common, Newbury District and Surrounding Areas
No full textThe airborne gamma ray survey recorded more than 40,000 scintillation spectra and 20,000 spectra from semiconductor detectors. The vehicular survey produced a further 1346 and 763 spectral sets respectively. The installation, calibration, recording and analysis followed SURRC procedures which have been developed and validated over many years and are fully documented. Pre flight checks on detector performance for energy calibration, energy resolution and sensitivity were performed on a daily basis. Background readings over water were taken on a daily basis. All data were registered and backed up in duplicate to form a digital archive of the survey. Subsequent analysis and mapping has used a combination of standard procedures established over many years, and new techniques developed to analyse the low energy spectra. All results have been retained to facilitate traceability and further analysis in the future. The sensitivity of the aircraft and vehicle were also checked at Greenham Common by collecting a set of 31 core samples for independent laboratory analysis.
The key points arising from the airborne survey of the entire area show that there has been sufficient sensitivity to record variations in the natural background. The levels of 137Cs are consistent with weapons' testing fallout, and are substantially lower than in other parts of the UK and Europe. The average levels of K (0.5%), U (1 ppm) and Th (3 ppm) are lower than national averages and show variations within the area which reflect local geology and landcover. The area as a whole therefore is one of low environmental radiation background compared with national averages. There is no evidence of signals at Greenham Common or in its vicinity which would present a local radiation hazard. However, signals were detected in the vicinity of Harwell and the Rutherford laboratory which would, at the time of the survey, represent radiation projected off-site as a result of materials stored on-site or on-site activities.
Examination of the low energy gamma ray spectra recorded from the semiconductor detectors reveals no evidence, within the sensitivity limits of the method, for excess gamma ray signals at the energies associated with 235U around Greenham Common, Newbury and Thatcham. The low energy data are sufficiently sensitive to record variations in the distribution of natural activity in the area. There is tentative evidence for 241Am in the vicinity of AWE Aldermaston.
The vehicular survey demonstrated that the grass areas in between the runway and taxi lanes, and around the hardstand associated with the 1958 fire have retained weapons' testing 137Cs. This supports the view that these represent authentic undisturbed areas for sampling. The built surfaces remaining at the time of the survey were of lower natural activity and 137Cs content than their surroundings. High resolution gamma ray spectra at selected sites were also consistent with the known sources of background radioactivity.
On the basis of the results, Newbury District and surrounding areas represent an area with low environmental radioactivity compared with national and European averages. There is no evidence to substantiate fears about the quality of the radiation environment in the vicinity of Greenham Common
An Aerial Gamma Ray Survey of Hunterston Nuclear Power Station in 14-15 April and 4 May 1994
No full textProgramming of formalin-induced nociception by neonatal LPS exposure: maintenance by peripheral and central neuroimmune activity
No full textAbstract not availableIhssane Zouikr, Abdulrzag F. Ahmed, Jay C. Horvat, Kenneth W. Beagley, Vicki L. Clifton, Allyson Ray, Rick F. Thorne, Andrew G. Jarnicki, Philip M. Hansbro, Deborah M. Hodgso
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