Distribution of plutonium isotopes in sediments of Melanesian Basin,Central Pacific

The anthropogenic plutonium isotopes are important geochemical tracers for environmental studies. The distributions and sources of the Pu isotopes in water column or sediments of the North Pacific have been intensively studied. However, knowledge on the distribution of Pu isotopes in sediments of the Central Pacific, when available, is limited. To study the composition of Pu isotopes in the ocean, thus to identify the sources of radioactive pollution, sediment core samples were collected in the Central Pacific by R/V Hakuho Maru in the KH-04-5 cruise. The activity concentrations of ^239+240Pu and the ²⁴⁰Pu/²³⁹Pu atom ratio were determined using a sector-field inductively coupled mass spectrometry (SF-ICP-MS) combined with a high efficiency sample introduction system (APEX-Q). Possible sources and sedimentation behavior of Pu isotopes are discussed.     

Determination of Pu isotopes in sediment cores in the Sea of Okhotsk and the NW Pacific by sector field ICP-MS

Summary Studies on the environmental behavior of plutonium in the marine environment require an analytical method with high sensitivity and capability to provide the isotopic composition of Pu in marine samples. In this work, as part of our on-going project on Pu environmental behavior in the Pacific Ocean, a sector field ICP-MS method combined with an off-line anion-exchange chromatography system was optimized for the determination of Pu and its atomic ratio of ²⁴⁰Pu/²³⁹Pu in sediment core samples. Using a conical concentric nebulizer and 150-second counting time, we were able to lower the detection limit of Pu down to 0.35 fg. The mass discrimination effect was evaluated using a mixed Pu isotope standard solution with certified a ²⁴⁰Pu/²³⁹Pu isotope ratio (NBS-947). The overall performance of the analytical method was validated by the determination of Pu and its isotope composition in an ocean sediment reference material (IAEA-368). Both the ^239+240Pu activity and ²⁴⁰Pu/²³⁹Pu atomic ratio were found to be in good agreement with the certified and/or literature values. As an important application, we employed the analytical method to investigate the vertical profiles of ^239+240Pu activity and ²⁴⁰Pu/²³⁹Pu atomic ratio in sediment cores in the Sea of Okhotsk and the NW Pacific. It was found that the Bikini close-in fallout Pu could be transported as far as the Sea of Okhotsk. The results provided evidence to support our hypothesis on the oceanic current transportation of Bikini close-in fallout Pu in the NW Pacific and its marginal seas.     

激光剥蚀-多接收电感耦合等离子体质谱法 测定含钚颗粒物中240 Pu/239 Pu比值

为高精度、准确地获取含钚颗粒物中具有核保障监督意义和核取证价值的钚同位素比值,建立了激光剥蚀-多接收电感耦合等离子体质谱(LA-MC-ICP-MS)测定含钚颗粒物中240 Pu/239 Pu的分析方法.采用检漏、安装排风罩和擦拭剥蚀池内壁等方式有效降低激光剥蚀产物沾污实验室和危及人身安全的潜在风险.联用扫描电迁移率粒径谱仪(SMPS)与激光剥蚀-多接收器等离子体质谱(LA-MC-ICP-MS)研究了激光剥蚀玻璃基体标样产生气溶胶的分布特性,结果表明,剥蚀产物的主要粒径是40~500 nm,应尽量采用水平管道连接激光剥蚀进样系统与MC-ICP-MS,含钚颗粒物分析后剥蚀池持续吹扫时间应大于15 min.采用外标归一化法离线校正质量分馏效应和离子计数器检测效率,建立了含钚颗粒物中240 Pu/239 Pu的LA-MC-ICP-MS分析方法,固定束斑直径30μm、脉冲重复率5 Hz、剥蚀时间5 s,调节能量密度使含钚颗粒物模拟样品中239 Pu的信号强度分别达2×104 cps和2×105 cps,本方法对240 Pu/239 Pu测量的相对实验标准不确定度小于1.4%(n=6),测量结果与参考值的相对偏差小于4.7%,仪器调试时间和单个样品测量时间分别为9.0和0.5 h.含钚颗粒物模拟样品分析结果表明,本方法精度高、结果准确、分析速度快,可满足核保障监督、禁产核查和核取证中含钚颗粒物直接分析的需求.     

Precise determination of Pu isotopes in a seawater reference material using ID-SF-ICP-MS combined with two-stage anion-exchange chromatography.

In order to obtain the precise Pu isotope composition of Irish Sea water reference material issued by the International Atomic Energy Agency (IAEA-381), we analyzed the activities of (239)Pu, (240)Pu and the atom ratio of (240)Pu/(239)Pu by a highly sensitive isotope dilution SF-ICP-MS method combined with two-stage chromatographic separation and purification. With a mean chemical yield of 65% for (242)Pu tracer, the experimentally established values for (239)Pu, (240)Pu and (239+240)Pu activities are in good agreement with the certified ones. For the (240)Pu/(239)Pu atom ratio, we obtain a value of 0.2315 +/- 0.0008 with a high precision (RSD, 0.35%), which is much more precise than the information value of 0.22 +/- 0.03 (RSD, 13.6%) provided by the IAEA certification report. The precise determination of Pu isotopes in this seawater reference material will be useful for the validation of analytical methods for the study of radionuclides in the marine environment.     

Determination of 237Np and Pu isotopes in large soil samples by inductively coupled plasma mass spectrometry

A new method for the determination of (237)Np and Pu isotopes in large soil samples has been developed that provides enhanced uranium removal to facilitate assay by inductively coupled plasma mass spectrometry (ICP-MS). This method allows rapid preconcentration and separation of plutonium and neptunium in large soil samples for the measurement of (237)Np and Pu isotopes by ICP-MS. (238)U can interfere with (239)Pu measurement by ICP-MS as (238)UH(+) mass overlap and (237)Np via (238)U peak tailing. The method provides enhanced removal of uranium by separating Pu and Np initially on TEVA Resin, then transferring Pu to DGA resin for additional purification. The decontamination factor for removal of uranium from plutonium for this method is greater than 1×10(6). Alpha spectrometry can also be applied so that the shorter-lived (238)Pu isotope can be measured successfully. (239) Pu, (242)Pu and (237)Np were measured by ICP-MS, while (236)Pu and (238)Pu were measured by alpha spectrometry.     

Measurement of240Pu/239Pu ratio by fission track method and inductively coupled plasma mass spectrometry

Fission track /FT/ method and inductively coupled plasma mass spectrometry /ICP-MS/, that is a new analytical technique for the analysis of trace element, were used for the measurement of²⁴⁰Pu/²³⁹Pu ratios in environmental samples. The results obtained by both methods are in agreement within the relative deviation of 9–13%. The precision in ICP-MS was found to be better than in it the FT-method. These methods are applicable to measure the Pu isotopes ratio at low concentration levels in environmental samples.     

Determination of plutonium and its isotopic ratio in marine sediment samples using quadrupole ICP-MS with the shield torch system under normal plasma conditions

An analytical method for determining ²³⁹Pu and ²⁴⁰Pu in marine sediment samples, which uses quadrupole ICP-MS, was developed in this work. A simple anion-exchange chromatography system was employed for the separation and purification of Pu from the sample matrix. A sufficient decontamination factor of 1.4×10⁴ for U, which interferes with the determination of ²³⁹Pu, was achieved. High sensitivity Pu determination was obtained, which led to an extremely low concentration detection limit of ~8 fg/ml (0.019 mBq/ml for ²³⁹Pu; 0.071 mBq/ml for ²⁴⁰Pu) in a sample solution, or an absolute detection limit of 42 fg in a 5 ml sample solution, by using the shield torch technique. Analytical results for the determination of the ^239+240Pu and the ²⁴⁰Pu/²³⁹Pu ratio in IAEA 368 (ocean sediment) reference material indicated that the accuracy of the method was satisfactory. The method developed was successfully applied to a study of Pu behavior in the sediments from Sagami Bay, Japan. The observed high ²⁴⁰Pu/²³⁹Pu ratio in the sediment core indicated that there was additional Pu input derived from close-in fallout in addition to the global fallout.     

ICP-MS analysis of plutonium activities and <Superscript>240</Superscript>Pu/<Superscript>239</Superscript>Pu ratio in alpha spectrometry planchet deposits

Plutonium isotopes were measured by alpha-spectrometry and ICP-MS in sediment samples from two European lakes: Blelham Tarn in U.K. and Stechlin lake in Germany. The ICP-MS measurements were made after alpha-spectrometry counting of the planchets. The planchets were prepared by traditional electrodeposition method after radiochemical extraction, separation and purification of the Pu fraction. A short radiochemical separation using plutonium selective resin, between the two spectrometry measures, is presented. The results show that these two complementary methods are in good agreement, the plutonium activity concentrations are the same. Alpha-spectrometry allows the ²³⁸Pu determination and ICP-MS individual measurement of ²³⁹Pu and ²⁴⁰Pu. ²³⁸Pu/^239+240Pu and ²⁴⁰Pu/²³⁹Pu ratios are calculated to determine the plutonium contamination source. With the results of these two techniques, it could be demonstrate that the plutonium is of global fallout origin.     

Determination of plutonium isotopes in seawater samples by Semiconductor Alpha Spectrometry,ICP-MS and AMS techniques

Analysis of plutonium isotopes by Semiconductor Alpha Spectrometry (SAS), ICP-sector field mass spectrometry (ICP-MS) and Accelerator Mass Spectrometry (AMS) was carried out in seawater samples collected from the Northeast Atlantic Ocean (nuclear waste dumping sites) and Northwest Pacific Ocean. No particularly elevated levels of the atom ratios of ²⁴⁰Pu/²³⁹Pu compared to global fallout ratio (0.18) were found in the Northeast Atlantic Ocean seawater samples. The higher levels of atom ratios of ²⁴⁰Pu/²³⁹Pu were found in the Northwest Pacific Ocean. This is mainly due to contribution from the local fallout from nuclear weapon tests carried out at the Pacific Proving Grounds at the Marshall Islands.     

Determination of plutonium-239 + plutonium-240 and plutonium-241 in environmental samples using low-level liquid scintillation spectrometry.

A radiochemical method for the simultaneous determination of 239Pu + 240Pu and 241Pu in environmental samples has been developed. In the course of the analysis a 236Pu tracer was used for estimating the chemical yield of plutonium isotopes. After suitable pre-treatment of the sample, the plutonium nuclides in solution were coprecipitated with iron(III) hydroxide and calcium oxalate and isolated further from impurities and interfering radionuclides by means of anion-exchange chromatography. Plutonium isotopes in the eluate (NH4I-HCI) were converted into nitrate form and then extracted with 20 ml of 5% bis(2-ethylhexyl) hydrogen phosphate extractive cocktail. The final organic solution was measured spectrometrically using an ultra-low-level liquid scintillation spectrometer, Quantulus (LKB, 1220 Wallac). The chemical yields of plutonium range from 25 to 50% for 100 I of sea-water and 30 to 60% for 40 g of dried soil sample. The counting efficiencies are nearly 100% for 239Pu + 240Pu and 48.8% for 241Pu, respectively. The detection limits were estimated to be 0.20 mBq for 239Pu + 240Pu and 2.2 mBq for 241Pu, respectively. The proposed procedure has been tested for the simultaneous determination of 239Pu + 240Pu and 241Pu in sea-water (Irish Sea, North Sea) and soils (Cumbrian coast, UK; Byelorussia, USSR).     

Isotope ratio analysis of individual sub-micrometer plutonium particles with inductively coupled plasma mass spectrometry

Information on plutonium isotope ratios in individual particles is of great importance for nuclear safeguards, nuclear forensics and so on. Although secondary ion mass spectrometry (SIMS) is successfully utilized for the analysis of individual uranium particles, the isobaric interference of americium-241 to plutonium-241 makes difficult to obtain accurate isotope ratios in individual plutonium particles. In the present work, an analytical technique by a combination of chemical separation and inductively coupled plasma mass spectrometry (ICP-MS) is developed and applied to isotope ratio analysis of individual sub-micrometer plutonium particles. The ICP-MS results for individual plutonium particles prepared from a standard reference material (NBL SRM-947) indicate that the use of a desolvation system for sample introduction improves the precision of isotope ratios. In addition, the accuracy of the ²⁴¹Pu/²³⁹Pu isotope ratio is much improved, owing to the chemical separation of plutonium and americium. In conclusion, the performance of the proposed ICP-MS technique is sufficient for the analysis of individual plutonium particles.     

Determination of plutonium isotopes in marine particles collected by the large volume in situ filtration and concentration system

An analytical method for the determination of ²³⁹Pu and ²⁴⁰Pu in marine particle samples by sector field high-resolution ICP-MS was developed. The method was applied for large and small particle samples (particle diameter: >70 μm and 1–70 μm, respectively, collected with a large volume in situ filtration and concentration system at different depths in the water column off Rokkaho, Japan, where the spent nuclear fuel reprocessing plant of Japan Nuclear Fuel Ltd. has started test operation since March 2006.     

Development of a bipolar electrolysis system for tritium accumulation in HTO

Due to the different ²⁴⁰Pu/²³⁹Pu atom ratios from different sources of Pu in the environment, Pu isotopes have been widely used for source identification of radionuclides in sediments. In this work, using sector-field ICP-MS, we investigated Pu inventory and its isotopic composition in a lacustrine sediment core collected in Chenghai Lake, SW China. The ²⁴⁰Pu/²³⁹Pu atom ratios in this sediment core ranged from 0.166 to 0.271 with a mean of 0.195±0.021, which was slightly higher than that of global fallout. The ^239+240Pu/¹³⁷Cs activity ratios ranged from 0.0155 to 0.0411, with a mean of 0.0215, and the ^239+240Pu inventory was 35.4 MBq/km²; both ^239+240Pu/¹³⁷Cs activity ratio and Pu inventory were close to those values of global fallout at 20–30 °N. Three peaks were observed for both ¹³⁷Cs and ^239+240Pu activities in the examined sediment core; they most probably indicated the maximum deposition of global fallout between 1963 and 1964, the fallout from a series of Chinese nuclear tests during the 1970s, and the deposition of resuspended Pu-bearing particles from the Chernobyl accident. Therefore, the vertical profile of Pu isotopes should provide useful time markers for rapid dating of recent sediments. These authors contributed equally to this work.     

Rapid method for the analysis of plutonium isotopes in a soil sample within 60 min.

A rapid method for the determination of Pu isotopes in a soil sample within 60 min of starting sample pretreatment was developed. The large reduction in the analysis time was attained by the rapid and perfect digestion of the sample using an alkaline fusion method with an induction heating machine. Pu concentrations were then determined by flow injection/ICP-MS using a solid extraction resin after preconcentration by batch extraction with a chelate resin. The limits of detection for 239Pu and 240Pu were 9.2 fg and 4.3 fg, corresponding to 0.03 and 0.05 Bq kg(-1), respectively, under our analytical conditions, which satisfy the lower detection limits (0.5 Bq kg(-1) of 239Pu, and 2 Bq kg(-1) of 240Pu) required for rapid analysis techniques by the Ministry of Education, Culture, Sports, Science and Technology, Japan. This method provides a powerful and practical technique for emergency monitoring in and around nuclear facilities that handle large amounts of plutonium.     

Determination of (236)U and transuranium elements in depleted uranium ammunition by alpha-spectrometry and ICP-MS

It is well known that ammunition containing depleted uranium (DU) was used by NATO during the Balkan conflict. To evaluate the origin of DU (the enrichment of natural uranium or the reprocessing of spent nuclear fuel) it is necessary to directly detect the presence of activation products ((236)U, (239)Pu, (240)Pu, (241)Am, and (237)Np) in the ammunition. In this work the analysis of actinides by alpha-spectrometry was compared with that by inductively coupled plasma mass spectrometry (ICP-MS) after selective separation of ultratraces of transuranium elements from the uranium matrix. (242)Pu and (243)Am were added to calculate the chemical yield. Plutonium was separated from uranium by extraction chromatography, using tri- n-octylamine (TNOA), with a decontamination factor higher than 10(6); after elution plutonium was determined by ICP-MS ((239)Pu and (240)Pu) and alpha-spectrometry ((239+240)Pu) after electroplating. The concentration of Pu in two DU penetrator samples was 7 x 10(-12) g g(-1) and 2 x 10(-11) g g(-1). The (240)Pu/(239)Pu isotope ratio in one penetrator sample (0.12+/-0.04) was significantly lower than the (240)Pu/(239)Pu ratios found in two soil samples from Kosovo (0.35+/-0.10 and 0.27+/-0.07). (241)Am was separated by extraction chromatography, using di(2-ethylhexyl)phosphoric acid (HDEHP), with a decontamination factor as high as 10(7). The concentration of (241)Am in the penetrator samples was 2.7 x 10(-14) g g(-1) and <9.4 x 10(-15) g g(-1). In addition (237)Np was detected at ultratrace levels. In general, ICP-MS and alpha-spectrometry results were in good agreement.The presence of anthropogenic radionuclides ((236)U, (239)Pu,(240)Pu, (241)Am, and (237)Np) in the penetrators indicates that at least part of the uranium originated from the reprocessing of nuclear fuel. Because the concentrations of radionuclides are very low, their radiotoxicological effect is negligible.     

A combined method for the determination of the isotopic vector of plutonium isotopes in environmental samples

A combination of alpha-spectrometry, liquid scintillation counting (LSC) and accelerator mass spectrometry (AMS) was used for the determination of plutonium isotopes. ²³⁸Pu and ^239+240Pu were measured by alpha-spectrometry after separation of Pu by anion-exchange using ²³⁶Pu tracer as recovery monitor. After alpha-measurement, one part of the sample was dissolved for determining ²⁴¹Pu by LSC. Another part was used for the measurement of the ²⁴⁰Pu/²³⁹Pu atom ratio by AMS at VERA. Thus, it was possible to obtain complete information on the Pu isotopic composition of the samples. This method was applied to environmental reference samples and samples contaminated from nuclear reprocessing.     

Large volume preconcentration and purification for determining the240Pu/<Superscript>239</Superscript>Pu isotopic ratio and <Superscript>238</Superscript>Pu/<Superscript>239+240</Superscript>Pu alpha-activity ratio in seawater

Summary The present paper describes a new analytical method for determining the ²⁴⁰Pu/²³⁹Pu isotopic ratio and ²³⁸Pu/^239+240Pu α -activity ratio in seawater, both of which are important parameters for determining Pu sources in the ocean. Plutonium isotopes were preconcentrated from a large volume of seawater (4700-10800 liter) by solid phase extraction using MnO₂-impregnated fibers and eluted into 3M HCl. After the elution, the Pu species of all oxidation states were converted to Pu(IV) using NaNO₂, purified by solvent extraction using thenoyltrifluoroacetone (TTA)-benzene, and concentrated in 5 ml of 0.2M HNO₂. The ²⁴⁰Pu/²³⁹Pu and ²³⁸Pu/^239+240Pu ratios in the 5-ml final solution were determined by inductively coupled plasma-mass spectrometry (ICP-MS) and α-spectrometry, respectively. A pg level of Pu, which was a sufficiently large amount for the determination, was obtained by the solid phase extraction. Through the redox conversion and solvent extraction, the Pu species, such as Pu(III), Pu(IV) and Pu(VI), were collected at a high recovery of 96±2% (n=3) despite the presence of large amounts of Mn, and interfering ²³⁸U (3.3 μg^. l^-1in seawater) was effectively removed with a decontamination factor of 1.7·10⁷. The accuracy of the method for the ²⁴⁰Pu/²³⁹Pu ratio was verified using reference materials of seawater and a terrestrial soil sample. The present technique was applied to the determination of the ²⁴⁰Pu/²³⁹Pu and ²³⁸Pu/^239+240Pu ratios in coastal and oceanic water.     

Determination of plutonium and other transuranic elements by inductively coupled plasma mass spectrometry: A historical perspective and new frontiers in the environmental sciences

Inductively coupled plasma mass spectrometry (ICPMS), particularly with sector field mass analyzers (SF-ICPMS), has emerged in the past several years as an excellent analytical technique for rapid, highly sensitive determination of transuranic elements (TRU) in environmental samples. SF-ICPMS has advantages of simplicity of sample preparation, high sample throughput, widespread availability in laboratories worldwide, and relatively straightforward operation when compared to other competing mass spectrometric techniques. Arguably, SF-ICPMS is the preferred technique for routine, high-throughput determination of ²³⁷Np and the Pu isotopes, excepting ²³⁸Pu, at fg-pg levels in environmental samples. Many research groups have now demonstrated the SF-ICPMS determination of ^239 + 240Pu activities, ²⁴⁰Pu/²³⁹Pu and other Pu atom ratios in several different application areas. Many studies have examined the relative contribution of global fallout vs. local/regional Pu sources in the environment through measurement of ²⁴⁰Pu/²³⁹Pu and, in some cases, ²⁴¹Pu/²³⁹Pu and ²⁴²Pu/²³⁹Pu. “Stratospheric fallout”, which was deposited from thermonuclear tests, conducted largely during the 1952–1964 time period, is characterized by a well-defined ²⁴⁰Pu/²³⁹Pu of ~ 0.18, while most other sources have different ratios. Examples of local/regional Pu sources are the Nevada Test Site, the Chernobyl plume, and accidents at Palomares, Spain and Thule, Greenland. The determination of Pu activities and atom ratios has stimulated much interest in the use of Pu as a marine tracer; several studies have shown that Pu is transported over long distances by ocean currents. ²⁴⁰Pu/²³⁹Pu ratios > 0.20 in sediments and seawater of the North Pacific are ascribed to ocean current transport of fallout from the Pacific Proving Ground. In nuclear forensics, much effort is focused on detection and fingerprinting of small amounts of TRU in environmental samples consisting of bulk material or individual isolated particles. Activity measurements of ^239 + 240Pu, determined by SF-ICPMS, have the potential to supplement and/or replace ¹³⁷Cs as a tracer of erosion, deposition, and sedimentation. Undoubtedly, the application of SF-ICPMS in TRU analysis will continue to expand, witness new developments, and generate interesting unforeseen applications in upcoming years.     

Determination of alpha-emitting Pu isotopes in environmental samples

This paper presents an improved radiochemical procedure for the determination of alpha-emitting Pu isotopes in environmental samples (soils, sediments, vegetation) by alpha-particle spectrometry. Quantitative Pu recovery yields were obtained (average 60%), 0.1 mBq being the average minimum detectable activity by the complete technique. Special efforts were made to ensure the removal of traces of different natural alpha-emitting radionuclides, which can interfere with the correct determination of 239+240Pu and 238Pu concentrations. The radiochemical procedure was validated by application to reference material and by participation in intercomparison exercises. This radiochemical procedure was applied to the different layers of a high-resolution sediment core taken from a lake in Sweden. The 239+240Pu and 238Pu/239+240Pu profiles obtained in the high-resolution sediment core correctly reproduced the expected evolution of these quantities as observed historically in the atmosphere, validating the procedure for this purpose and showing the power of these radionuclides for dating purposes.     

Identification of the contamination source of plutonium in environmental samples with isotopic ratios determined by inductively coupled plasma mass spectrometry and alpha-spectrometry

Concentrations of^239+249Pu in environmental samples were detemined by ICP-MS and spectrometry, showing consistent results, which suggests an applicability of ICP-MS to²³⁹Pu and²⁴⁰Pu measurement. The activity ratios of²³⁸Pu/^239+240Pu and²⁴⁰Pu/²³⁹Pu were significantly different in samples from the general environment and near Sellafield reprocessing plants, indicating the usefulness of these ratios for identification of the Pu contamination source.