Determination of plutonium isotopes (238Pu, 239Pu, 240Pu, 241Pu) in environmental samples using radiochemical separation combined with radiometric and mass spectrometric measurements

Quantitative estimation of dust transport in the desert region of northwest China by plutonium isotopes

Dust is an important source of atmospheric pollution, and quantitative estimation of desert dust transport is crucial for air pollution control. In this study, five typical sandy soil profiles in the Tengger Desert were collected and analyzed for 239,240Pu concentration and 240Pu/239Pu atomic ratios in order to identify the source of 239,240Pu in this area and explore the sedimentary characteristics of dust in different profiles. The results revealed that the concentrations of 239,240Pu in the soil profiles were between 0.002 and 0.443 mBq/g with an exception of the deep layer soil at one site. The measured atomic ratios of 240Pu/239Pu are at the global atmospheric fallout level with a mean of 0.184 ± 0.020, indicating that global fallout is the dominant source of plutonium in this region. The total inventories of 239,240Pu in the reference sites in this area were estimated to be 39.2-44.6 Bq/m2, this is in agreement with the value from the global fallout of atmospheric nuclear weapon tests at the similar latitude (30-40 °N: 42 Bq/m2). The estimated erosion rate in the erosion profile utilizing soil erosion intensity mode is 2491 t/km2/yr and the soil erosion depth is 9.86 cm, While, the stacking rate of the accumulation profile is 1383 t/km2/yr, and the depth of accumulation is estimated to be 5.48 cm. The difference between the erosion and accumulation profiles indicated that approximately 1107 t/km2/yr of dust was exported from the Gobi landform area of the Tengger Desert, which might be transported long distance in the downwind direction.

Rapid and Simultaneous Determination of 238Pu, 239Pu, 240Pu, and 241Pu in Samples with High-Level Uranium Using ICP-MS/MS and Extraction Chromatography

As the most important plutonium isotopes, 238Pu, 239Pu, 240Pu, and 241Pu are normally measured by two to three techniques, which are tedious, time-consuming, and not suitable for rapid analysis in emergency situations. Recently, ICP-MS has become a competitive technique for the rapid measurement of 239Pu, 240Pu, and 241Pu. However, ICP-MS is difficult to measure 238Pu due to the serious isobaric interference of 238U. This work reports a rapid analytical method to solve this problem for the simultaneous determination of 238Pu, 239Pu, 240Pu, and 241Pu using triple-quadrupole inductively coupled plasma mass spectrometry (ICP-MS/MS) combined with chemical separation. Chemical separation achieved a high decontamination factor of 2.12 × 109 for the most critical interfering element, uranium, by using two sequential TK200 columns. The interferences of 238U1H+ and 238U+ were effectively eliminated by using 12 mL/min He-6 mL/min NH3 as the reaction gases in the octupole collision/reaction cell in ICP-MS/MS. Combined with chemical separation, the overall elimination efficiency of 238U1H+ reached 3.6 × 1017, which is 105 times better than the reported method. With the high 238U+ elimination efficiency of 1.12 × 104 in the ICP-MS/MS measurement, the overall removal efficiency of 238U+ reached 1013, guaranteeing accurate determination of femtogram-level 238Pu as well as 239Pu, 240Pu, and 241Pu in the samples containing milligram-level 238U. The detection time is reduced to minutes, well fulfilling the requirement of rapid analysis. This method is validated by analyzing the standard reference material and the spiked samples.

Plutonium isotopes in the northwestern South China Sea: Level, distribution, source and deposition

The spatial distribution of plutonium isotopes (²³⁹Pu, ²⁴⁰Pu) in the surface sediments collected from the northwestern South China Sea (SCS) in 2018 was investigated. The ^239,240Pu concentrations in surface sediments vary from 0.048 to 0.960 mBq/g (with mean of 0.282 ± 0.242 mBq/g) depending on the geographical feature of the sampling location such as the river estuary, continental shelf, slope and deep basin. Higher ²⁴⁰Pu/²³⁹Pu atomic ratios (0.24-0.31) in the surface sediment of the SCS compared to the global fallout value of 0.18 were observed, this is attributed to the input of close-in fallout of the Pacific Proving Ground (PPG) transported by the North Equatorial Current and Kuroshio Current to the northern SCS. The contribution of the PPG derived plutonium in the SCS sediment was estimated to be 39%-78% using a simple two-end member mixing model based on the measured ²⁴⁰Pu/²³⁹Pu atomic ratios in the sediment. Besides the soluble ^239,240Pu level in seawater, load of suspended particulate matter from the river runoff and biological debris, hydrographic and hydrodynamic conditions are key parameters influencing the deposition process of plutonium to the sediment.

Rapid determination of plutonium isotopes in small samples using single anion exchange separation and ICP-MS/MS measurement in NH3-He mode for sediment dating

To accurately determine ultra-trace Pu isotopes in small environmental samples, we explored ICP-MS/MS in NH₃-He mode, and investigated mechanism of ²³⁸U interference removal and measurement sensitivity improvement for plutonium isotopes. The interference of uranium and uranium hydrides was effectively eliminated using 0.4 mL/min NH₃ as reaction gas by shifting them to U(NH_m)_n⁺ and UH(NH_m)_n⁺. The overall interference of uranium was reduced to <2.4 × 10^-7, while remaining excellent ²³⁹Pu sensitivity (13,900 Mcps/(mg/L)) mainly due to ion focusing effect of Pu by helium gas. On this basis, the purification of plutonium using a single AG1- × 4 column was proved to be sufficient for accurate determination of plutonium isotopes by the developed detection method, and the detection limits for the method were estimated to be 0.16 fg (0.4 μBq) for ²³⁹Pu, 0.046 fg (0.4 μBq) for ²⁴⁰Pu and 0.039 fg (0.15 mBq) for ²⁴¹Pu. The method was validated by analyzing plutonium isotopes in certificated reference materials and reported environmental samples of only 1-2 g. The analytical results of ultra-trace Pu isotopes in small amounts (∼1 g) of lake sediments obtained by the developed method were successfully applied to sediment dating.

Distinctive distribution and migration of global fallout plutonium isotopes in an alpine lake and its implications for sediment dating

This work investigated plutonium (Pu) isotopes in sediment cores collected from an alpine lake (Lake Heinongpo with 3779 m above sea level) in Southwestern China. ²⁴⁰Pu/²³⁹Pu atom ratios in all sediment samples showed the typical global fallout values of ∼0.18 without any influences from other Pu contaminant sources. ^239+240Pu activities with surface and subsurface maximums followed by exponential decline with sediment depth were respectively observed in the two sediment cores. The distinctive depth distributions of ^239,240Pu in the lake sediments was attributed to the very slow sediment deposition rate due to the lack of terrestrial sediment input, while the alpine snowmelt input was the primary source of Pu in the lake sediments in addition to the direct atmospheric deposition. The total Pu inventory was estimated to be 56.3 ± 1.4 and 63.9 ± 0.8 Bq/m² respectively in the two sediment cores. The generally higher Pu inventory in the Lake Heinongpo compared with other reported lakes in similar latitude should be mainly attributed to their different Pu input passages. The advection-diffusion equation was further applied to evaluate the downward migration of Pu isotopes in the sediment cores and predict the future evolution of Pu distribution in the sediment cores. The fitted results indicated that the diffusion effect controlled the downward migration of Pu in the sediments, but this diffusive migration will not prevent the peak of global fallout Pu in undisturbed sediment cores from being a valuable time marker for sediment dating.

Uncertainty and detection limits of 241Pu determination by liquid scintillation counting (LSC)

Determination of ²⁴¹Pu is an essential issue for radiation protection, as it is the precursor of some nuclides with high radiotoxicity. ²⁴¹Pu is a low energy beta emitter, which makes its measurement more challenging than that of Pu alpha emitters. The most widely used method for the measurement of ²⁴¹Pu is liquid scintillation counting (LSC). In this method, the assessment of Pu radiochemical yield is done by measuring the sample by alpha spectrometry before being lixiviated and measured by LSC. This double measurement affects uncertainty analysis, as well as decision threshold and detection limit, considering that both components of the total yield (radiochemical and lixiviation) should be contemplated. In this paper, and for quality assurance (QA) purposes, in-depth uncertainty and detection limit formulae for the proposed method, controlling correlations and considering all the parameters involved including chemical and lixiviation yields, have been developed. A sensitivity analysis of the uncertainty budget together with an assessment of ²⁴²Pu tracer quantity to be used, ensuring a total yield of at least 50% and a relative uncertainty of the leaching yield of at most 5%, have been carried out. In addition, an analysis of the impact of the real lixiviation yield value and its uncertainty on the results has been done. As a general conclusion, and considering the values of the parameters chosen for this work (samples of 1 g measured for 24 h by LSC), the ²⁴¹Pu uncertainties range from 5% to 30% depending on the activity concentration values and the detection limits range from 14 to 30 Bq kg^-1, depending on yield values. The main components of the uncertainty budget are the net ²⁴¹Pu and background counts obtained in the LSC measurement for low contaminated samples while this is the case for the alpha gross count rate in LSC measurement of the alpha calibration source for highly contaminated samples. In addition, an analysis of possible interference by Pu alpha emitters in the ²⁴¹Pu signal and a comparison of quench standard curves of ³H and ²⁴¹Pu are also performed.

Determination of ultra-trace level plutonium isotopes in soil samples by triple-quadrupole inductively coupled plasma-mass spectrometry with mass-shift mode combined with UTEVA chromatographic separation

Although triple-quadrupole inductively coupled plasma-mass spectrometry (ICP-MS/MS) has become an attractive technique for the measurement of long-lived radionuclides, the abundance sensitivity, isobaric and polyatomic ions interferences seriously restrict the application. The spectral peak tailing and uranium hydrides (UH⁺, UH₂⁺) from ²³⁸U have a serious influence on the accurate measurement of ²³⁹Pu and ²⁴⁰Pu, especially for the ultra-trace level plutonium isotopes in the higher uranium sample. A new method was developed using ICP-MS/MS measurement in mass-shift mode with collision-reaction gas combined with a chemical separation procedure. As O₂ readily converted Pu⁺ ion to PuO₂⁺, while disassociated the interfering diatomic ions of interfering elements (U, Pb, Hg, Tl, etc.), the interferences from these elements were completely eliminated if plutonium was detected as PuO₂⁺ at the m/z more than 270. By the mass filter in MS/MS mode combined with O₂ as reaction gas the lower peak tailing of ²³⁸U⁺ (<5 × 10^-12) was significantly suppressed. By this way, the ²³⁸UO₂H⁺/²³⁸UO₂⁺ atomic ratio was reduced to 4.82 × 10^-9, which is significantly lower than that of other collision-reaction gas modes. Interferences from Pb, Hg and Tl polyatomic ions were also completely eliminated. Thus, accurate measurement of ultra-trace level ²³⁹Pu in high uranium sample solutions with the ²³⁹Pu/²³⁸U concentration ratio of 10^-10 was achieved by the mass-shift mode with 0.15 mL/min O₂/He + 12.0 mL/min He as collision-reaction gas, and high elimination efficiency of uranium interferences up to 10¹⁴ can be obtained by combination with the chemical separation using a single UTEVA resin column. The developed method can be applied to accurately determine the fg level ²³⁹Pu in high uranium samples, such as large-size deep seawater, deep soil and sediment, uranium debris of nuclear fuel.

Simultaneous Isotopic Analysis of U, Pu, and Am in Spent Nuclear Fuel by Resonance Ionization Mass Spectrometry

Solid samples of spent nuclear fuel were analyzed for actinide isotopic composition by resonance ionization mass spectrometry. Isotopes of U, Pu, and Am were simultaneously quantified using a new method that removes and/or resolves the isobaric interferences at ²³⁸U/²³⁸Pu and ²⁴¹Pu/²⁴¹Am without sample preparation other than cutting and mounting small (∼10 μm) samples. Trends in burnup and neutron capture product distributions were correlated with the sampling positions inside the reactor. The results show the skin effect, in which the core and near-edge regions of a fuel pellet exhibit strong differences in actinide concentrations and isotope distributions due to differences in the neutron energy spectra between the pellet rim and the core. While no elemental concentration measurements were made, the ability to measure the ²³⁸Pu/²³⁹Pu ratio in the presence of a 7400× excess of ²³⁸U enabled an estimate of the enhancement in Pu concentration due to the skin effect at the rim of the pellet.

Radionuclides in sediments of the Aare and Rhine river system: Fallouts, discharges, depth-age relations, mass accumulation rates and transport along the river

The Aare-Rhine river system with its four nuclear power plants on the banks of these rivers and with its intermediate lakes and reservoirs provide the unique chance to analyze the input of radioactivity into the system thereby furnishing information on the sources, to analyze the transport within the sediment and along the rivers, and to refine unsupported ²¹⁰Pb dating validated by known discharge maxima. At three locations (Lake Biel, Klingnau Reservoir, old branch of the Rhine) in the Aare and Rhine rivers system downstream of the older nuclear power plants (NPPs) Mühleberg and Beznau, the vertical distributions of ¹³⁷Cs, ²¹⁰Pb, ²¹⁴Pb, ²¹⁴Bi, ⁴⁰K, ⁷Be, ²³⁹Pu, ²⁴⁰Pu, ²⁴¹Am, and ²³⁷Np in sediment cores were determined. Depth-age relations using the excess 210 Pb were established with the raw and with the piecewise Constant Rate Supply (CRS) models. A comparison of the piecewise CRS method with the imprints of known discharges showed differences of up to two years. Besides typical ¹³⁷Cs signals (about 100 Bq∙kg^-1) from the atmospheric nuclear weapons testing (NWT) and the Chernobyl fallouts, imprints of known ¹³⁷Cs discharges (10-70 Bq∙kg^-1) from the NPPs were found in the sediments. The ²³⁷Np distributions (6-10 Bq∙kg^-1) essentially follow the ¹³⁷Cs NWT distributions. In the sediment downstream the NPP Mühleberg (Lake Biel) a²³⁹Pu distribution (<3 Bq∙kg^-1) was found, which was solely due to the NWT fallout. Downstream the NPP Beznau (Klingnau Reservoir and an old branch of the Rhine), besides the NWT distribution, also imprints of ²³⁹Pu discharges (up to 7 Bq∙kg^-1) were found within the time interval 1963 to 1986.²⁴⁰Pu/²³⁹Pu ratios revealed that the burn-up times of the nuclear fuel in the NPP (²³⁵U enrichment of 3.5%), from which the discharges stem, should be about 1 year or less. A comparison between the calculated and the measured ¹³⁷Cs/²³⁹Pu ratio revealed no large discrepancies for the Lake Biel and Rhine positions, but in the Klingnau distribution, the calculated ¹³⁷Cs/²³⁹Pu ratio is one order of magnitude larger than the measured one. The reason could be either a natural uranium research reactor as the source, or strong, short-range ²³⁹Pu precipitation after the discharge from the Beznau NPP. The largest ²³⁹Pu peak in the Rhine sediment (1968/70) corresponds to no major peak in the Klingnau sediment. For the NPP Mühleberg discharge of 1982 the ratio of the ¹³⁷Cs deposition in sediments from Lake Biel, Klingnau Reservoir and the Rhine river is about 1 : 0.5 : 2.9. For the 1977/78 ²³⁹Pu deposition the ratio is 1 : 0.02, for the Klingnau Reservoir and the Rhine sediments, respectively. These numbers indicate a long-range transport of Cs and a rather short-range transport of Pu.

Determination of Pu-239 in Urine by Sector Field Inductively Coupled Plasma Mass Spectrometry (SF-ICP-MS) Using an Automated Offline Sample Preparation Technique

Here we report a new procedure to determine Pu-239 in urine using a custom-made automated pre-analytical processing system (single probe) with Pu-242 as a tracer followed by analysis by SF-ICP-MS. An average Pu-242 recovery rate of 88% was obtained with CF-ThU-1000 columns reused >100 times. Analytical results agree with measurements obtained using the CDC manual method with a R2 of 0.9994. Results for Oak Ridge National Laboratory (ORNL) reference materials (RM) align with target values with a bias range of -3.44% to 3.05%. The limit of detection for this method is 0.63 pg/L, which is comparable to previous manual methods.

Method for determination of Pu isotopes in soil and sediment samples by inductively coupled plasma mass spectrometry after simple chemical separation using TK200 resin

Plutonium has been extensively studied in the environment, for the purpose of radiological assessment, environmental behavior study and nuclear emergency response. To determine Pu isotopes in environmental soil and sediment, a novel analytical method was established in this study using a new type of extraction resin, TK200 resin. Firstly an investigation was performed to study the extraction behaviors of Pu, U, Th, Hg, Tl, Pb, Bi and Hf on TK200 resin. On the basis of the results, a new chromatographic procedure was then proposed to separate Pu from the elements that interfere the accurate determination of Pu isotopes by mass spectrometry. Owing to the excellent separation efficiency between Pu and interfering elements (IEs) of the developed procedure, high decontamination factors (DFs) were obtained for IEs, e.g. the DF(U) (>7.5 × 10⁷) was the highest reported value. The separation procedure was finally combined with HNO₃ leaching, CaF₂/LaF₃ coprecipitation and sector field-inductively coupled plasma mass spectrometry (SF-ICPMS) measurement to establish a complete method. The established method was evaluated by analyzing four standard reference materials (soil, sediment), and the results showed that both ^239+240Pu activity and ²⁴⁰Pu/²³⁹Pu isotopic ratio were accurately determined, with stable and high Pu chemical recoveries (81-91%). The whole analytical method only took about 15 h, and the limits of detection were calculated to be 0.13-0.24 fg g^-1 for Pu isotopes (for 2 g soil or sediment), guaranteeing the rapid determination of ultra-trace level Pu in soil and sediment samples.

Determination of plutonium isotopes in environmental samples by extraction chromatography with triisooctylamine - polyethylene resin

Method for determination of plutonium isotopes in various environmental samples is presented. The separation and purification of plutonium is attained by extraction chromatography with triisooctylamine - polyethylene resin in nitric and hydrochloric acid media. Plutonium is measured by alpha-particle spectrometry after electrodeposition on a stainless steel disk. The analytical quality was checked by analyzing reference materials with different matrices from IAEA (Soil-6, IAEA-375, IAEA-384, IAEA-414) and NPL (AL-2009, AL-2010, AL-2011, AL-2013, AB-2014). The major advantages of the method are the low cost of the analysis, high radiochemical yields and high decontamination factors from the matrix elements, natural and man-made radionuclides.

Sedimentary record of plutonium in the North Yellow Sea and the response to catchment environmental changes of inflow rivers

Plutonium (Pu) isotopes were first determined in surface and core sediment samples collected from the northern North Yellow Sea (NYS) to elucidate their source terms and deposition process as well as the response to catchment environmental changes of inflow rivers. ²⁴⁰Pu/²³⁹Pu atom ratios in all sediments showed the typical global fallout value of ∼0.18 without any influences from the nuclear weapons tests conducted recently in the North Korea or early in the Pacific Proving Ground. The large variation of ^239+240Pu activities (0.022-0.515 mBq/g) observed in surface sediments should be mainly attributed to the re-suspension and transportation of fine sediments influenced by the Liaonan Costal Current. Based on the two ^239+249Pu depth profiles with easily observed onset fallout levels (1952) and global fallout peaks (1963), ^239+240Pu served as a valid time mark in the coastal sedimentary system. Riverine input Pu contributed only 15-27% to the total global fallout inventory (92.5-108.8 Bq/m²) in the northern NYS, much lower than that in the Yangtze River estuary (77-80%), indicating a better soil conservation in the northeast China due to higher forest coverage compared to the Yangtze River's drainage basin. The increase of riverine input Pu after 1980s reflected the more intense soil erosion degree caused by the land use and cover change due to the increment of human activities in the northeast China at the same period. Our results demonstrated that plutonium is a good indicator for studying sedimentary process and its response to the environment in the coastal area.

Association of Plutonium isotopes with natural soil particles of different size and comparison with 137Cs

Information on how plutonium (Pu) isotopes associate with natural soil particles of different size is very important for the interpretation involved in the application of Pu isotopes as soil erosion tracers. This work investigated the association of Pu isotopes with different particle size fractions of natural soils and compared it with that of ¹³⁷Cs. Ten bulk soils collected from two different areas were separated into different particle size fractions by a combination of wet sieving and centrifugation techniques and the sub-samples were analyzed for ¹³⁷Cs, ²³⁹Pu and ²⁴⁰Pu. Results showed that the concentrations of both ^239+240Pu and ¹³⁷Cs increase with decreased particle sizes and are closely related to the specific surface areas of soil particles, which demonstrated a similar preferential association of Pu with finer soil particles as ¹³⁷Cs. The activity ratios of ^239+240Pu/¹³⁷Cs in soil fractions increasing with increased particle size further indicated a less preferential transport of Pu with fine particles compared to ¹³⁷Cs. These results not only highlight the suitability of Pu isotopes as soil erosion tracers, but also provide useful information for assessing the migration behavior of Pu in contaminated environments.

Determination of (241)Pu by the method of disturbed radioactive equilibrium using 2πα-counting and precision gamma-spectrometry

A simple technique is proposed for the determination of the content of (241)Pu, which is based on disturbance of radioactive equilibrium in the genetically related (237)U←(241)Pu→(241)Am decay chain of radionuclides, with the subsequent use of 2πα-counting and precision gamma-spectroscopy for monitoring the process of restoration of that equilibrium. It has been shown that the data on dynamics of accumulation of the daughter (241)Am, which were obtained from the results of measurements of α- and γ-spectra of the samples, correspond to the estimates calculated for the chain of two genetically related radionuclides, the differences in the estimates of (241)Pu radioactivity not exceeding 2%. Combining the different methods of registration (2πα-counting, semiconductor alpha- and gamma-spectrometry) enables the proposed method to be efficiently applied both for calibration of (241)Pu-sources (from several hundreds of kBq and higher) and for radioisotopic analysis of plutonium mixtures. In doing so, there is a deep purification of (241)Pu from its daughter decay products required due to unavailability of commercial detectors that could make it possible, based only on analysis of alpha-spectra, to conduct quantitative analysis of the content of (238)Pu and (241)Am.

Anthropogenic radionuclide fluxes and distribution in bottom sediments of the cooling basin of the Ignalina Nuclear Power Plant

Based on γ-ray emitting artificial radionuclide spectrometric measurements, an assessment of areal and vertical distribution of (137)Cs, (60)Co and (54)Mn activity concentrations in bottom sediments of Lake Drūkšiai was performed. Samples of bottom sediments from seven monitoring stations within the cooling basin were collected in 1988-1996 and 2007-2010 (in July-August). For radionuclide areal distribution analysis, samples from the surface 0-5 cm layer were used. Multi sample cores sliced 2 cm, 3 cm or 5 cm thick were used to study the vertical distribution of radionuclides. The lowest (137)Cs activity concentrations were obtained for two stations that were situated close to channels with radionuclide discharges, but with sediments that had a significantly smaller fraction of organic matter related to finest particles and consequently smaller radionuclide retention potential. The (137)Cs activity concentration was distributed quite evenly in the bottom sediments from other investigated monitoring stations. The highest (137)Cs activity concentrations in the bottom sediments of Lake Drūkšiai were measured in the period of 1988-1989; in 1990, the (137)Cs activity concentrations slightly decreased and they varied insignificantly over the investigation period. The obtained (238)Pu/(239,240)Pu activity ratio values in the bottom sediments of Lake Drūkšiai represented radioactive pollution with plutonium from nuclear weapon tests. Higher (60)Co and (54)Mn activity concentrations were observed in the monitoring stations that were close to the impact zones of the technical water outlet channel and industrial rain drainage system channel. (60)Co and (54)Mn activity concentrations in the bottom sediments of Lake Drūkšiai significantly decreased when operations at both INPP reactor units were stopped. The vertical distribution of radionuclides in bottom sediments revealed complicated sedimentation features, which may have been affected by a number of natural and anthropogenic factors resulting in mixing, resuspension and remobilization of sediments and radionuclides. The associated with particles (137)Cs flux was 129 Bq/(m(2) year). The (137)Cs transfer rate from water into bottom sediments was 14.3 year(-1) (or, the removal time was 25 days). The Kd value for (137)Cs in situ estimated from trap material was 80 m(3)/kg. The associated with particles (60)Co flux was 21 Bq/(m(2) year), when (60)Co activity concentration in sediment trap particles was 15.7 ± 5 Bq/kg. (60)Co activity concentration in soluble form was less than the minimum detectable activity (MDA = 1.3 Bq/m(3)). Then, the conservatively derived Kd value for (60)Co was >90 m(3)/kg.

Spatial patterns and ratios of ¹³⁷Cs, ⁹⁰Sr, and Pu isotopes in the top layer of undisturbed meadow soils as indicators for contamination origin

Spatial distribution of activity concentrations of (137)Cs, (90)Sr, and (239,240)Pu in the top layer of undisturbed meadow soils was compared between two regional transects across Lithuania: one in the SW region, more affected by the Chernobyl radioactive fallout, and the other in the NE region. Radiochemical, γ-, α-, β-, and mass spectrometric methods were used to determine the radionuclide activity. Our results validate that higher activity concentrations in the top soil layer were present in the SW region, despite the fact that sampling was performed after 22 years of the Chernobyl Nuclear Power Plant (NPP) accident. Using the activity concentration ratio (137)Cs/(239,240)Puglobal, the contribution of the Chernobyl NPP accident to the total radiocesium activity concentrations in these meadow soils was evaluated and found to be in the range of 6.5-59.1%. Meanwhile, the activity concentration ratio (238)Pu/(239,240)Pu showed that Chernobyl-derived Pu occurred at almost half of the sampling sites. The locations with maximal values of 47% of Chernobyl-derived Pu material were close to northeastern Poland, where deposition of most of non-volatile radioisotopes from the Chernobyl plume was determined.

Plutonium as a tracer for soil erosion assessment in northeast China

Soil erosion is one of the most serious environmental and agricultural problems faced by human society. Assessing intensity is an important issue for controlling soil erosion and improving eco-environmental quality. The suitability of the application of plutonium (Pu) as a tracer for soil erosion assessment in northeast China was investigated by comparing with that of 137Cs. Here we build on preliminary work, in which we investigated the potential of Pu as a soil erosion tracer by sampling additional reference sites and potential erosive sites, along the Liaodong Bay region in northeast China, for Pu isotopes and 137Cs. 240Pu/239Pu atomic ratios in all samples were approximately 0.18, which indicated that the dominant source of Pu was the global fallout. Pu showed very similar distribution patterns to those of 137Cs at both uncultivated and cultivated sites. 239+240Pu concentrations in all uncultivated soil cores followed an exponential decline with soil depth, whereas at cultivated sites, Pu was homogenously distributed in plow horizons. Factors such as planted crop types, as well as methods and frequencies of irrigation and tillage were suggested to influence the distribution of radionuclides in cultivated land. The baseline inventories of 239+240Pu and 137Cs were 88.4 and 1688 Bq m(-2) respectively. Soil erosion rates estimated by 239+240Pu tracing method were consistent with those obtained by the 137Cs method, confirming that Pu is an effective tracer with a similar tracing behavior to that of 137Cs for soil erosion assessment.