137Cs Peak Research Articles

Gamma-gamma coincidence performance of LaBr3:Ce scintillation detectors vs HPGe detectors in high count-rate scenarios

A radiation detection system consisting of two cerium doped lanthanum bromide (LaBr3:Ce) scintillation detectors in a gamma-gamma coincidence configuration has been used to demonstrate the advantages that coincident detection provides relative to a single detector, and the advantages that LaBr3:Ce detectors provide relative to high purity germanium (HPGe) detectors. Signal to noise ratios of select photopeak pairs for these detectors have been compared to high-purity germanium (HPGe) detectors in both single and coincident detector configurations in order to quantify the performance of each detector configuration. The efficiency and energy resolution of LaBr3:Ce detectors have been determined and compared to HPGe detectors. Coincident gamma-ray pairs from the radionuclides 152Eu and 133Ba have been identified in a sample that is dominated by 137Cs. Gamma-gamma coincidence successfully reduced the Compton continuum from the large 137Cs peak, revealed several coincident gamma energies characteristic of these nuclides, and improved the signal-to-noise ratio relative to single detector measurements. LaBr3:Ce detectors performed at count rates multiple times higher than can be achieved with HPGe detectors. The standard background spectrum consisting of peaks associated with transitions within the LaBr3:Ce crystal has also been significantly reduced. It is shown that LaBr3:Ce detectors have the unique capability to perform gamma-gamma coincidence measurements in very high count rate scenarios, which can potentially benefit nuclear safeguards in situ measurements of spent nuclear fuel.

Estimation of sedimentation rates based on the excess of radium 228 in granitic reservoir sediments

Knowledge of sedimentation rates in lakes is required to understand and quantify the geochemical processes involved in scavenging and remobilization of contaminants at the Sediment-Water Interface (SWI). The well-known 210Pb excess (210Pbex) method cannot be used for quantifying sedimentation rates in uranium-enriched catchments, as large amounts of 210Pb produced by weathering and human activities may dilute the atmospheric 210Pb. As an alternative dating method in these cases, we propose an original method based on 232Th decay series nuclides.This study focuses on an artificial lake located in a granitic catchment downstream from a former uranium mine site. The exponential decay of 228Ra excess (228Raex) with depth in two long cores yields sedimentation rates of 2.4 and 5.2 cm yr−1 respectively. These sedimentation rates lead to the attribution of the 137Cs activity peak observed at depth to the Chernobyl fallout event of 1986. The 228Raex method was also applied to two short cores which did not display the 137Cs peak, and mean sedimentation rates of 2.1 and 4.0 cm y−1 were deduced. The proposed method may replace the classical radiochronological methods (210Pbex, 137Cs) to determine sedimentation rates in granitic catchments.

Multiple sediment cores from reservoirs are needed to reconstruct recent watershed changes from stable isotopes (δ13C and δ15N) and C/N ratios: case studies from the mid-western United States

Watershed land-use changes, including urbanization, have caused accelerated soil erosion, which in turn has increased sediment accumulation rates in most aging reservoirs in the mid-western United States (USA), thereby posing a threat to their longevity and productivity. We analyzed three sediment cores from each of two reservoirs in the mid-western USA, the Webber Dam impoundment in Michigan and Goshen Pond in Indiana. Core chronologies were established using 137Cs and 210Pb. Concentrations of organic carbon and nitrogen and their stable isotope compositions (δ13C and δ15N) were measured to investigate past land-use changes. We used three excess 210Pb-based (210Pbxs) sedimentation rate models (constant 210Pb flux and sedimentation, constant rate of supply of 210Pb and constant initial 210Pb concentration) to develop core chronologies and compared them to the chronology obtained from the 137Cs peak. Validation of the excess 210Pb-based chronology with137Cs-based chronology requires more than one 210Pbxs-based-model. That is, even in one watershed, output from more than one 210Pbxs-based model may have to be compared with an independent time marker. We compared C/N ratios, δ13C and δ15N among three time horizons in each of the three cores from the reservoirs (corresponding to dates of 1950, 1970 and 2010). Within a reservoir, there can be large differences between cores for a given time horizon, indicating there could be spatial differences in sources of C and N and the processes that influence carbon and nitrogen isotopes. We conclude that multiple sediment cores from reservoirs should be analyzed if carbon and nitrogen isotopes in sediments are to be used for paleoenvironmental inference.

Sediment accumulation rates and high-resolution stratigraphy of recent fluvial suspension deposits in various fluvial settings, Morava River catchment area, Czech Republic

We present a comprehensive study concerning sedimentary processes in fluvial sediment traps within the Morava River catchment area (Czech Republic) involving three dammed reservoirs, four meanders and oxbow lakes, and several natural floodplain sites. The objective of the study was to determine sediment accumulation rates (SAR), estimate erosion rates, calculating these using a combination of the 137Cs method and historical data. Another purpose of this study was to provide insight into changing erosion and accumulation rates over the last century. Extensive water course modifications were carried out in the Morava River catchment area during the twentieth century, which likely affected sedimentation rates along the river course. Other multiproxy stratigraphic methods (X-ray densitometry, magnetic susceptibility, and visible-light reflectance spectrometry) were applied to obtain additional information about sediment infill. Sediment stratigraphy revealed distinct distal-to-proximal patterns, especially in reservoirs. Granulometrically, silts and sandy silts prevailed in sediments. Oxbow lakes and meanders contained larger amounts of clay and organic matter, which is the main difference between them and reservoirs. Pronounced 137Cs peaks were recorded in all studied cores (maximum 377Bq·kg−1), thus indicating Chernobyl fallout from 1986 or older events. Calculated sediment accumulation rates were lowest in distal parts of reservoirs (0.13–0.58cm/y) and floodplains (0.45–0.88cm/y), moderately high rates were found in proximal parts of reservoirs and oxbow lakes (2.27–4.4cm/y), and the highest rates in some oxbow lakes located near the river (6–8cm/y). The frequency of the inundation still can be high in some natural areas as in the Litovelské Pomoraví protected area, whereas the decreasing frequency of the inundation in other modified parts can contribute to a lower sedimentation rate. The local effects such as difference between SARs in oxbow lakes and reservoirs, different grain size distribution in both systems, and high variability in thickness of their proximal and distal parts play a crucial role in the analysis of regional accumulation rates. Local effects are much stronger than regional effects, such as rainfall and land use. Combined with the low resolution of time scales (usually only three datums are available: reservoir construction datum, 137Cs fallout event, and top of sediment), these effects may obscure the general trends of regionally increasing or decreasing net SARs, making the analysis of erosion rates from the sedimentary record an extremely difficult task.

A Method to Determine Doublet Photopeak Area 137Cs and 214Bi, in NORM Soil by NaI-detector

Due to the poor resolution of (76 mm×76 mm) NaI scintillation detector, ~7.5% for 137Cs peak (661.5 keV), mutual spectral interference of environmental samples between 137Cs and 214Bi (609 keV) in the decay series of uranium peaks, is a serious problem. This overlapped problem appears in low-level sample spectrum causes overestimation of the specific activity of both nuclides. The main purpose of this work is to resolve this problem and to present a methodology to correct the activity concentrations of 137Cs by NaI(Tl) spectroscopy. In Duhok governorate of Iraq, as a real NORM case, the accumulation of 137Cs is significantly brought by west-north wind and precipitation in the years following nuclear weapons testing and Chernobyl accident in 1986. The developed correlations for any ratio of the measured areas of 214Bi and 137Cs overcome the overestimation and show very good results. The method is approved by comparing the relative error of the measured and corrected activity of Bi with that measured Pb. The maximum, minimum and average relative errors decreased from 40%, 7.3% and 19.4% to 6.1%, -6.5% and 0.6% respectively.

Establishing a tracer-based sediment budget to preserve wetlands in Mediterranean mountain agroecosystems (NE Spain)

Mountain wetlands in Mediterranean regions are particularly threatened in agricultural environments due to anthropogenic activity. An integrated study of source-to-sink sediment fluxes was carried out in an agricultural catchment that holds a small permanent lake included in the European NATURA 2000 Network. More than 1000yrs of human intervention and the variety of land uses pose a substantial challenge when attempting to estimate sediment fluxes which is the first requirement to protect fragile wetlands. To date, there have been few similar studies and those that have been carried out have not addressed such complex terrain. Geostatistical interpolation and GIS tools were used to derive the soil spatial redistribution from point 137Cs inventories, and to establish the sediment budget in a catchment located in the Southern Pyrenees. The soil redistribution was intense and soil erosion predominated over soil deposition. On the areas that maintained natural vegetation the median soil erosion and deposition rates were moderate, ranging from 2.6 to 6Mghayr−1 and 1.5 to 2.1Mghayr−1, respectively. However, in cultivated fields both erosion and deposition were significantly higher (ca. 20Mghayr−1), and the maximum rates were always associated with tillage practices. Farming activities in the last part of the 20th century intensified soil erosion, as evidenced by the 1963 137Cs peaks in the lake cores and estimates from the sediment budget indicated a net deposition of 671Mgyr−1. Results confirm a siltation risk for the lake and provide a foundation for designing management plans to preserve this threatened wetland. This comprehensive approach provides information useful for understanding processes that influence the patterns and rates of soil transfer and deposition within fragile Mediterranean mountain wetlands subjected to climate and anthropogenic stresses.

Background radiation reduction for a high-resolution gamma-ray spectrometer used for environmental radioactivity measurements

A detailed analysis is presented of background radiation spectra for a high-resolution gamma-ray spectrometer used to measure environmental radioactivity, for various shielding configurations. The main goal is to improve the detection limits of low-level activity measurements by reducing the background as much as possible. Passive shielding configurations are used to decrease the total background counting rate by adding new layers. Subsequently, for the maximum shielding configuration, the Minimum Detectable Activity (MDA) is improved by at least 13-fold for 137Cs, 8-fold for 214Bi (609.31keV), 7-fold for 40K and 5.5-fold for 208Tl (2614.53keV). A reduction factor of 240 for the 137Cs peak (counting rate) at maximum shielding and an insignificant peak for this radionuclide was determined. For other radionuclides, peaks below the detection limit of the detector system were also found. These results show that the shielding was successful in reducing and removing peaks from the background spectrum.

A simple method for activity determination of 134Cs and 137Cs in foodstuffs using NaI(Tl) scintillation spectrometer

A simplified peak fitting technique for the analysis of the overlapped pulse-height spectra of 134Cs and 137Cs γ-rays obtained with a NaI(Tl) scintillation spectrometer was studied. In this analysis, nearly an upper half of 662keV 137Cs peak data was employed for fitting of the Gaussian peak using the least squares algorithm. Consistent results were obtained as compared with the reference value of test samples mixed with 134Cs and 137Cs standard solutions.

Use of 137Cs and 210Pbex measurements on deposits in a karst depression to study the erosional response of a small karst catchment in Southwest China to land‐use change

AbstractKarst depressions represent important sinks for sediment, and such sediment can provide a valuable record of the impact of environmental change on soil erosion rates. However, the sediment dynamics of karst depressions are not well understood. This contribution reports a study of the small catchment of a karst depression in Southwest China, with a drainage area of 0.054 km2, aimed at using the sediment deposits in the depression to reconstruct the erosional response of the catchment to land‐use change and, more particularly, the deforestation which took place in 1979. 137Cs and 210Pbex are used as both chronometers and as tracers. Five cores, collected from the bottom of a depression, with an area of 2652 m2, showed similar 137Cs depth distributions, with a single 137Cs peak, which was attributed to the 1979 deforestation. The 137Cs activity associated with the peaks varied between 5.68 ± 0.64 and 9.19 ± 0.99 Bq kg–1. The average depth of sediment deposition between 1979 and 2008 deduced from the depths of the 1979 137Cs peak was 74.1 cm. The existence of relatively high 210Pbex activity of 66.33 ± 8.44 Bq kg–1 in the upper section (0–16 cm) of the core analyzed for 210Pbex suggests that recent sedimentation has been very limited. Net erosion rates on the hillslopes contributing runoff and sediment t to the depression were estimated to be 5258 t km–2 year–1 from 1979 to 1990 and 256 t km–2 year–1 from 1991 to 2008, respectively. The high sediment yield in the first period was associated with the severe soil erosion triggered by the 1979 deforestation, which resulted from the changes in land ownership immediately after the Cultural Revolution. Soil erosion has been very limited since 1990 because the thin soils had been totally removed from many parts of the karst slopes and the soils remaining on the other parts of the slopes have been protected by terracing or vegetation rehabilitation. Copyright © 2012 John Wiley & Sons, Ltd.

Multiple dating of varved sediments from Lake Łazduny, northern Poland: Toward an improved chronology for the last 150 years

On two short sediment cores from Lake Łazduny (northeastern Poland) different methods for age estimation were applied including varve counting, 210Pb, 137Cs and OSL dating. The investigated sediment consists of finely laminated, organic-rich calcareous gyttja interrupted by a sand layer. For 210Pb we tested the CFCS, CIC, CRS and SIT models and compared the results with the established varve chronology and the 137Cs distribution. The total 210Pb activity distribution is consistent between cores and shows a regular decrease with depth. However, the total inventory of unsupported 210Pb was significantly different and indicates varying rates of sediment focusing. Our results show that all 210Pb dating models used in this study produced different results, while the SIT model performed best in comparison with varve counts and 137Cs peaks. The CFCS model produced a realistic age-depth trend but obtained ages were too old compared to the varve time scale. The age estimates provided by the CRS model were too old as well with an increasing offset downcore and the CIC model failed completely by producing an unrealistic chronology with age inversions. This confirms that only systematic testing of different 210Pb dating models and routine validation using independent time markers produces reliable 210Pb chronologies. OSL dating of two samples from the sand layer provided much too old results which indicate incomplete bleaching during deposition of the analyzed quartz grains. This multiple dating approach demonstrates the considerable potential but also potential pitfalls of dating such young sediments.

Using Chernobyl‐derived 137Cs to document recent sediment deposition rates on the River Plava floodplain (Central European Russia)

AbstractFloodplain sedimentation is one of the most dynamic geomorphic processes within plain and lowland landscapes. There is generally a good understanding of longer term floodplain evolution, but quantitative information on overbank deposition rates for recent shorter timescales is lacking. This paper describes the application of Chernobyl‐derived 137Cs to quantify floodplain aggradation rates for the River Plava (a small river draining a severely contaminated part of the upland region of Central European Russia), based on detailed sampling of four representative floodplain study sites. Two approaches have been employed for estimating post‐Chernobyl (1986–2009) floodplain accumulation rates. The first was based simply on locating the Chernobyl fallout‐associated 137Cs peak in overbank sediment sections. The second involved quantification of the increase in the total 137Cs inventory at individual sampling points associated with the post‐Chernobyl deposition of contaminated suspended sediment. It has been shown that considerable local‐scale variability of overbank deposition rates exists, with aggradation rates on the low level floodplain (6 ± 1.2–14 ± 2.8 mm year−1) exceeding by 1.5–3 times the values for the middle level floodplain (2 ± 0.4–9 ± 1.8 mm year−1) and by 3–6 times the values for the upper level floodplain (1 ± 0.2–5 ± 1.0 mm year−1) floodplain levels. Combining these estimates with information on the areas occupied by different floodplain levels within the 54 km long valley section, derived from detailed geomorphic surveys of the selected reaches, it has been estimated that about 9700 ± 1950 t of sediment have been stored on floodplain during the 1986–2009 period. The role of floodplain storage in the overall basin sediment budget and conveyance losses within the main channel system have been evaluated. Copyright © 2012 John Wiley & Sons, Ltd.

Identification of deep subaqueous co-seismic scarps through specific coeval sedimentation in Lesser Antilles: implication for seismic hazard

Abstract. During the GWADASEIS cruise (Lesser Antilles volcanic arc, February–March 2009) a very high resolution (VHR) seismic-reflection survey was performed in order to constrain Late Quaternary to Present faulting. The profiles we obtained evidence frequent "ponding" of reworked sediments in the deepest areas, similar to the deposition of Mediterranean "homogenites". These bodies are acoustically transparent (few ms t.w.t. thick) and are often deposited on the hanging walls of dominantly normal faults, at the base of scarps. Their thickness appears sufficient to compensate (i.e. bury) co-seismic scarps between successive earthquakes, resulting in a flat and horizontal sea floor through time. In a selected area (offshore Montserrat and Nevis islands), piston coring (4 to 7 m long) was dedicated to a sedimentological analysis of the most recent of these particular layers. It corresponds to non-stratified homogenous calcareous silty sand (reworked calcareous plankton and minor volcanoclastics). This layer can be up to 2 m thick, and overlies fine-grained hemipelagites. The upper centimeters of the latter represent the normal RedOx water/sediment interface. 210Pb and 137Cs activities lack in the massive sands, while a normal profile of unsupported 210Pb decrease is observed in the hemipelagite below, together with a 137Cs peak corresponding to the Atmospheric Nuclear Experiments (1962). The RedOx level was thus capped by a recent instantaneous major sedimentary event considered as post-1970 AD; candidate seismic events to explain this sedimentary deposits are either the 16 March 1985 earthquake or the 8 October 1974 one (Mw = 6.3 and Mw = 7.4, respectively). This leads to consider that the syntectonic sedimentation in this area is not continuous but results from accumulation of thick homogenites deposited after the earthquakes (as observed in the following weeks after Haiti January 2010 event, McHugh et al., 2011). The existence of such deposits suggests that, in the area of study, vertical throw likely results from cumulated effects of separated earthquakes rather than from aseismic creep. Examination of VHR profiles shows that all major co-seismic offsets are recorded in the fault growth sequence and that co-seismic offsets can be precisely estimated. By using a sedimentation rate deduced from 210Pb decrease curve (0.5 mm yr−1) and taking into account minor reworking events detected in cores, we show that the Redonda system may have been responsible for five >M6 events during the last 34 000 yr. The approach presented in this work differs from fault activity analyses using displaced sets of isochronous surfaces and postulating co-seismic offsets. Combining VHR seismic imagery and coring we can decipher co-seismic vs. slow continuous displacement, and thus actually estimate the amplitude and the time distribution of major co-seismic offsets.

Compton-edge-based energy calibration of double-sided silicon strip detectors in Compton camera

Accurate energy calibration of double-sided silicon strip detectors (DSSDs) is very important, but challenging for high-energy photons. In the present study, the calibration was improved by considering the Compton edge additionally to the existing low-energy calibration points. The result, indeed, was very encouraging. The energy-calibration errors were dramatically reduced, from, on average, 15.5% and 16.9% to 0.47% and 0.31% for the 356 ( 133Ba) and 662 keV ( 137Cs) peaks, respectively. The imaging resolution of a double-scattering-type Compton camera using DSSDs as the scatterer detectors, for a 22Na point-like source, also was improved, by ∼9%.

Impact of dynamic feedbacks between sedimentation, sea-level rise, and biomass production on near-surface marsh stratigraphy and carbon accumulation

Salt marshes accrete both organic and inorganic sediments. Here we present analytical and numerical models of salt marsh sedimentation that, in addition to capturing inorganic processes, explicitly account for above- and belowground organic processes including root growth and decay of organic carbon. The analytical model is used to examine the bias introduced by organic processes into proxy records of sedimentation, namely 137Cs and 210Pb. We find that accretion rates estimated using 210Pb will be less than accretion rates estimated using the 137Cs peak in steadily accreting marshes if (1) carbon decay is significant and (2) data for 210Pb extend below the 137Cs peak. The numerical model expands upon the analytical model by including belowground processes such as compaction and root growth, and by explicitly tracking the evolution of aboveground biomass and its effect on sedimentation rates. Using the numerical model we explore how marsh stratigraphy responds to sediment supply and the rate of sea-level rise. It is calibrated and tested using an extensive data set of both marsh stratigraphy and measurements of vegetation dynamics in a Spartina alterniflora marsh in South Carolina, USA. We find that carbon accumulation in marshes is nonlinearly related to both the supply of inorganic sediment and the rate of sea-level rise; carbon accumulation increases with sea-level rise until sea-level rise reaches a critical rate that drowns the marsh vegetation and halts carbon accumulation. The model predicts that changes in carbon storage resulting from changing sediment supply or sea-level rise are strongly dependent on the background sediment supply: if inorganic sediment supply is reduced in an already sediment poor marsh the storage of organic carbon will increase to a far greater extent than in a sediment-rich marsh, provided that the rate of sea-level rise does not exceed a threshold. These results imply that altering sediment supply to estuaries (e.g., by damming upstream rivers or altering littoral sediment transport) could lead to significant changes in the carbon budgets of coastal salt marshes.

Determining the Chernobyl impact on sediments of a pre-Alpine lake with a very comprehensive set of data

Man-made and natural radionuclides in Lake Wallersee were determined in the pre-Alpine environment at the northern slope of the Alps, which was heavily affected by the Chernobyl fallout in May 1986. The objective of this study was to get knowledge of location and quantity of man-made radionuclide input (especially 137Cs) generated in the Chernobyl accident to lake sediments. Eleven sediment cores were sampled and activity depth profiles of 137Cs and 210Pb were determined with 5 mm depth-resolution. The Chernobyl fallout produced an extreme 137Cs peak in the sediment cores providing an excellent time marker. The chronological interpretation of deeper sediment layers was done by radiochemical analysis of 90Sr and 239+240Pu, which were released during atmospheric weapons' tests in the 1950s and 1960s. This allowed a complete chronological analysis of the sediment cores with a very compact set of data.

Persistent Chlordane Concentrations in Long Island Sound Sediment: Implications from Chlordane, 210Pb, and 137Cs Profiles

Concentrations of chlordane, a banned termiticide and pesticide, were examined in recently collected surficial sediment (10 sites) and sediment cores (4 sites) in Long Island Sound (LIS). The highest chlordane concentrations were observed in western LIS, near highly urbanized areas. Chlordane concentrations did not decrease significantly in the past decade when compared to the data collected in 1996, consistent with the observation of near-constant chlordane levels in blue mussel tissues collected during the same time period. Chlordane concentrations in many of the sites exceeded levels above which harmful effects on sediment-dwelling organisms are expected to frequently occur. Chlordane concentrations in two of the four sediment cores showed a peak below the sediment surface, suggesting reduced chlordane inputs in recent years. The lack of a chlordane concentration maximum below the sediment surface in the other two cores, coupled with the lack of a well-defined 137Cs peak, indicated significant sediment mixing. Simulations of 137Cs and 210Pb profiles in sediment cores with a simple sediment-mixing model were used to constrain both the deposition rate and the bioturbation rate of the sediment. Simulations of the chlordane profiles indicated continued chlordane input to LIS long after chlordane was phased out in the U.S. Continued chlordane input and significant sediment mixing may have contributed to the persistent chlordane concentrations in surficial sediment, which poses long-term threats to benthic organisms in LIS.

Retrospective of radioactive fallout from data on sampled bottom sediments in closed water bodies

A method for identifying past radiation events from dated layers of bottom sediments in stagnant water bodies is described. Results of an experimental study (2005–2006) of the samples of bottom sediments in the pond of the Timiryazev dendropark in Moscow are considered. The sediment layers are dated with 210Pb. The same radionuclide is used as a tracer for calculating the rate of sedimentation in the pond, which is estimated at 0.3–0.4 cm/year. The maximum 137Cs values are detected in the 0–24 cm column at depths of 7 and 13 cm. The 137Cs peak at a depth of 13 cm is dated as 1963, which reflects the maximum global fallout from the atmospheric nuclear weapon tests. A small peak of this radionuclide at 7 cm is dated as 1986. It appears to be attributed to the long-range fallout after the Chernobyl NPP accident. The origin of the 137Cs maximum at a depth of 13–14 cm is confirmed by characteristic ratios of radionuclide pairs available in the global fallout in the Moscow region. The ratios of 90Sr/137Cs = 0.6 and 239,240Pu/137Cs = 0.03 in the 13–14 cm layer are characteristic of the global radioactive fallout from nuclear explosions. In the layers above this maximum, such ratios vary sharply toward the enhanced 137Cs content in the fallout.

Floodplain sedimentation rates in an alpine watershed determined by radionuclide techniques

AbstractVertical profiles of the activities of 137Cs and 210Pb were measured on floodplain sediment cores and upland soil cores along the Soda Butte Creek and the Yellowstone River to determine floodplain sedimentation rates. The position of mine tailings from a 1950 impoundment failure was used as a stratigraphic marker to estimate the sedimentation rates and to make comparisons with rates provided by radionuclide‐based methods. Mass accumulation (sedimentation) rates calculated from the position of the mine tailings ranged from 0·00 to 0·17 g cm−2 yr−1 and were in good agreement with sedimentation rates calculated from the inventories of 137Cs and 210Pb. Sedimentation rates calculated from the position of the 137Cs peak generally overestimated the sedimentation rates, probably because of increased downward migration of 137Cs caused by the low pH of water moving through the mine tailings or the high permeability of floodplain sediments relative to upland reference soils. This study demonstrates that the 137Cs and 210Pb inventory methods for determining sedimentation rates can be applied to an alpine floodplain where sedimentation events are episodic and where orographic effects on precipitation generate strong downstream gradients in the delivery of atmospheric radionuclides. Copyright © 2007 John Wiley & Sons, Ltd.

137Cs budget during the period of 1960s in a small drainage basin on the Loess Plateau of China

A sediment profile with a thickness of 28.12 m in a failed reservoir in a small catchment of the Yuntaishan Gully in the Loess Plateau of China consisted of 44 flood couplets deposited during the period from 1960 to 1970 with total volume of 2.36 × 10 6 m 3. Specific sediment yields for a flood event varied from 300 t km −2 to 14,400 t km −2 and annual sediment yields varied from 2500 t km −2 in 1966 to 40,000 t km −2 in 1964 with a mean value of 12,700 t km −2 a −1 for the period. Average annual 137Cs concentrations of the sediments increased from 0.92 Bq kg −1 in 1960 to 4.82 Bq kg −1 in 1963, then decreased to 1.53 Bq kg −1 in 1970. The total 137Cs activity in the reservoir sediments was 9.22 × 10 9 Bq, which accounted for 31.9% of the total 137Cs fallout precipitation of 2.89 × 10 10 Bq within the catchment during the period. The proportion of the 137Cs loss from the catchment to the 137Cs fallout precipitation within the catchment in a year varied between 8.01% and 66.8%, and it was 20.9% for the peak 137Cs deposition year of 1963 and 52.0% in 1964. By analysis of the 137Cs budget in the catchment for the 137Cs peak precipitation period from 1962 to 1964, the 137Cs surface enrichment coefficient Γ should be much less than 0.23. And for calculation of soil losses on the cultivated land in the inter-gully area by using the Mass Balance Model II, the value of Γ should be 0.05–0.1.

High-resolution historical records from Pettaquamscutt River basin sediments: 1. 210Pb and varve chronologies validate record of 137Cs released by the Chernobyl accident

Cesium-137 derived from the explosion of the Chernobyl reactor in 1986 was preserved in anoxic sediments from a coastal environment in southern Rhode Island. Although the radioactive plume was detected in surface air samples at several locations in the United States, this is the first known record of a Chernobyl 137Cs peak in sediments from North America. The inventory of Chernobyl 137Cs that was preserved in the Pettaquamscutt River is small compared to European counterparts and should only be detectable for the next 15–20 yr. However, the presence of two 137Cs peaks (1963 and 1987) identifies a well-dated segment of the sediment column that could be exploited in understanding the decomposition and preservation of terrestrial and aquatic organic matter. Different methods for calculating the 210Pb chronology were also evaluated in this study and checked against independent varve counting. The end result is a detailed chronology of a site well suited for reconstruction of historical records of environmental change.