Origin and release date assessment of environmental plutonium by isotopic composition

The origin and release date of environmental plutonium have been assessed by the measurement of plutonium and americium isotopic composition. The applicability and sensitivity of different plutonium isotope ratios, ²⁴⁰Pu/²³⁹Pu and ²⁴¹Pu/²³⁹Pu measured by inductively coupled plasma sector field mass spectrometry and ²³⁸Pu/²³⁹Pu analysed by alpha spectrometry, have been evaluated for origin determination in several types of environmental samples. With use of mixing models the contribution of different sources (e.g. global fallout or Chernobyl) can be calculated. By the measurement of the ²⁴¹Am/²⁴¹Pu isotope ratio, the release date (i.e. formation of ²⁴¹Pu by irradiation) can be estimated in environmental samples, which is an important parameter to distinguish recent plutonium release from previous (e.g. Chernobyl) emissions.     

Improved method for the quantitative determination of ultra trace level of Pu-239+240 in siliceous base samples using microwave assisted dissolution

Mobilisation of alpha emitting radionuclides from silicious base sample is one the challenging task for environmental radiochemist. During this study, rapid and complete dissolution of the siliceous base samples were carried out by optimizing temperature, pressure and power of the microwaves. The Pu-239+240 in digested samples was pre-concentrated by scavenging Fe as Fe(OH)₃. Pu-239+240 was isolated from the Fe(OH)₃ by co-precipitating Pu with Bi(PO₄) in HNO₃ medium at pH 2. Pu-239+240 was separated from Bi(PO₄) and other transuranics by passing through cation and anion exchange resin. Pu-239+240 was counted by alpha spectrometry after electroplating on stainless steel planchet. The detection limits achieved for Pu-239+240 was 60 μBq/g (2.6 × 10⁻¹⁴ g/g). Pu-242 was used as a tracer for the evaluation of recovery of Pu-239+240. Samples prepared after complete destruction of matrix in microwave, showed 10–20% higher concentration of Pu-239+240 compared to conventional acid leached. Consistent recovery in the range of 97–99% for Pu-242 were observed in microwave digested samples whereas inconsistent results were observed in acid leached samples where the recoveries were in the range of 75–86%. Siliceous matrix degradation was tracked by monitoring the surface morphology and composition of the residue left at various stages of digestion using Scanning Electron Microscope (SEM) coupled with Energy dispersive X-ray spectrometer (EDS).     

Geographical distribution of plutonium derived from the atomic bomb in the eastern area of Nagasaki

In order to know the distribution of plutonium derived from the Nagasaki atomic bomb, soil samples were measured to determine the ²⁴⁰Pu/²³⁹Pu isotope ratio of and concentrations of ^239+240Pu and ¹³⁷Cs. The ^239+240Pu concentrations in soils, except for Nishiyama area, were close to the average concentration of soil collected in Japan. In soils collected at the Nishiyama area and at the eastern area of Nagasaki Prefecture and at part of northern area in Kumamoto Prefecture, the ²⁴⁰Pu/²³⁹Pu ratios were lower than the global fallout values. This suggests that plutonium from the atomic bomb was deposited in the eastern area from the hypocenter reaching up to 100 km eastwards.     

A gamma-spectrometric method for the determination of plutonium isotope ratios

A gamma-spectrometric method using an intrinsic high resolution germanium detector has been developed for the determination of isotope ratios of plutonium from samples in solution form. The method is based on the assay of low energy gamma-rays of²³⁸Pu,²³⁹Pu,²⁴⁰Pu and²⁴¹Pu and does not require the use of branching intensities or the knowledge of detection efficiencies for different gamma rays. Since low energy gamma-rays are used, the effect of²⁴¹Am has also been studied. It is found that results are not affected up to 0.5 wt% of²⁴¹Am in plutonium samples. An accuracy of 3% is achievable in the determination of²⁴⁰Pu/²³⁹Pu and²⁴¹Pu/²³⁹Pu atom ratios as demonstrated by carrying out measurements on isotopic standards of plutonium.     

The dynamic movement of plutonium in an underground nuclear test with implications for the contamination of groundwater

Summary The recent discovery of the migration of plutonium in groundwater away from underground nuclear tests at the Nevada Test Site has spawned considerable interest in the mechanisms by which plutonium may be released to the environment by a nuclear explosion. A suite of solid debris samples was collected during drilling through an expended test cavity and the overlying collapse chimney. Uranium and plutonium were analyzed for isotope ratios and concentrations using high precision magnetic sector inductively coupled mass spectrometry. The data unequivocally shows that plutonium may be dispersed throughout the cavity and chimney environment at the time of the detonation. The ²³⁹Pu/²⁴⁰Pu ratios are also fractionated relative to initial plutonium isotope ratio for the test device. Fractionation is the result of the volatilization of uranium and production of ²³⁹Pu by the reaction ²³⁸U(n,γ). We conclude that for the test under consideration plutonium was deposited outside of the confines of the cavity by dynamic processes in early-time and it is this plutonium that is most likely transferred to the groundwater regime.     

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.     

Accelerator mass spectrometry (AMS) in plutonium analysis

The paper summarizes the results of the ²⁴⁰Pu/²³⁹Pu atomic ratio studies in atmospheric fallout samples collected in 1986 over Gdynia (Poland) as well as three Baltic fish species collected in 1997 using the accelerator mass spectrometry. A new generation of AMS has been developed during last years and this method is an efficient and good technique to measure long-lived radioisotopes in the environment and provides the most accurate determination of the atomic ratios between ²⁴⁰Pu and ²³⁹Pu. The nuclide compositions of plutonium in filter samples correspond to their means of production. AMS measurements of atmospheric fallout collected in April showed sufficient increase of the ²⁴⁰Pu/²³⁹Pu atomic ratio from 0.28 from March to 0.47. Also such high increase of ²⁴⁰Pu/²³⁹Pu atomic ratio, close to reactor core ²⁴⁰Pu/²³⁹Pu atomic ratio, was observed in September and equaled 0.47.     

Rapid determination of 239Pu in urine samples using molecular recognition technology product AnaLig®Pu-02 gel

This paper describes the use of IBC′s AnaLig^®Pu-02 molecular recognition technology product to effectively and selectively pre-concentrate, separate and recover plutonium from urine samples. This method uses two-stage column separations consisting of two different commercial products, Eichrom’s Pre-filter Material and AnaLig^®Pu-02 resin from IBC Advanced Technologies. By eliminating the co-precipitation techniques and the ashing steps to remove residual organics, the analysis time was reduced significantly. The method was successfully tested by adding known activities of reference solutions of ²⁴²Pu and ²³⁹Pu to urine samples.     

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 Pu-239 content in Pu–Be neutron sources using Gamma-ray spectrometry

The need to determine the content of plutonium in Pu–Be neutron sources of Russian provenience arises from the administrative regulations applying to nuclear materials. The determination of a plutonium (all isotopes) amount was based on the measurement of an activity Pu-239. Gamma-ray spectrometry with semiconductor detector HPGe was applied. The determination of plutonium (all isotopes) amount was based on the measurement of Pu-239 activity by means of Gamma-ray spectrometry with semiconductor detector HPGe. Gamma lines of radionuclides Am-241, Pu-238, Pu-239 and Pu-241 were detected in spectra. Detection efficiencies were calculated by Monte Carlo method using MCNP4A code. Computations were done for several hypothetical plutonium amounts. Activities determined from peak areas of 129 and 413 keV photons emitted from Pu-239 were confronted. The right amount was established under the condition of equality of both activities.     

An inter-calibration campaign using various selected Pu spike isotopic reference materials

In nuclear safeguards, precise and accurate isotopic analyses are needed for two major elements from the nuclear fuel cycle: uranium and plutonium. This can be achieved by Isotope Dilution Mass Spectrometry (IDMS), which is one of the most reliable analytical techniques for the determination of plutonium amount content to a high level of accuracy. In order to achieve reliable isotope measurements isotopic reference materials with certified amount of plutonium and isotopic composition are required. At the Institute for Reference Materials and Measurements (IRMM) various plutonium spike reference materials for isotopes ²³⁹Pu, ²⁴⁰Pu, ²⁴²Pu and ²⁴⁴Pu are available. This enabled the setup of an inter-calibration campaign inter-linking selected plutonium spikes on a metrological basis applying state-of-the-art measurement procedures. The aim of this campaign is threefold: firstly to perform measurements on selected plutonium spike isotopic reference materials for quality control purposes, secondly to verify the amount content and the isotopic composition of the recently produced IRMM-1027m large sized dried (LSD) spikes and thirdly to demonstrate IRMM’s measurement capabilities for plutonium analysis via external quality tools. The obtained results using various spike isotopic reference materials will be presented and discussed in this paper. The measurement uncertainties of the IDMS results were calculated according to the guide to the expression of uncertainty in measurement (GUM).     

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 activity concentrations and <Superscript>240</Superscript>Pu/<Superscript>239</Superscript>Pu atom ratios in Brown Algae (<Emphasis Type="Italic">Fucus distichus</Emphasis>) collected from Amchitka Island,Alaska

Plutonium-239 (²³⁹Pu) and plutonium-240 (²⁴⁰Pu) activity concentrations and ²⁴⁰Pu/²³⁹Pu atom ratios are reported for Brown Algae (Fucus distichus) collected from the littoral zone of Amchitka Island (Alaska), and at a control site at Unalaska, Alaska. The average ²⁴⁰Pu/²³⁹Pu atom ratio observed in dried F. distichus collected from Amchitka Island was 0.227 ± 0.007 (N = 5) and compares with the expected ²⁴⁰Pu/²³⁹Pu atom ratio in integrated worldwide fallout deposition in the Northern Hemisphere of 0.1805 ± 0.0057. In the absence of any evidence of a local source of plutonium containing an elevated ²⁴⁰Pu/²³⁹Pu isotopic signature, the characteristically high ²⁴⁰Pu/²³⁹Pu content of F. distichus supports the view of the existence of a discernible, basin-wide non-fallout source of plutonium entering the subarctic Pacific.     

Low-level determination of plutonium by gamma and L X-ray spectroscopy

We have developed an analytical method for detection of²³⁹Pu in aqueous samples at concentrations as low as 10^–10M. This nuclear counting technique utilizes the uranium L X-rays, which follow the alpha-decay of plutonium. Because L X-rays are specific for the element and not for the individual isotope, the isotopic composition of the plutonium sample must be known. The counting efficiency in the 11–23 keV range is determined from a plutonium standard, and the concentration of the sample is then calculated from the L X-ray count and the isotopic composition. The total L X-ray count is corrected for possible contributions from other radionuclides present as impurities by measuring the low-energy gamma-spectrum for each contaminant to establish specific photon/X-ray ratios. The ratios are important when²⁴¹Pu and²⁴²Pu are measured, because the respective decay chain members produce non-U L X-rays. This new method can replace the use of labor-intensive radiochemical separation techniques and elaborate activation methods for analysis of²³⁹Pu in aqueous samples. It is also applicable for assaying plutonium in liquid wastes that pose possible hazards to the environment.     

Determination of 239,240Pu, 238Pu isotopes in soil samples using molecular recognition technology product AnaLig?Pu-02 gel

Procedure for analysis of plutonium isotopes in soil samples was developed using a new molecular recognition technology product AnaLig^?Pu-02 gel. Extraction chromatography TEVA^? Resin was used for purification of plutonium phase to remove thorium impurities which interfere in Pu determination by alpha spectrometry. The performance of the method was successfully tested by analysis of a sand stimulant sample and a soil sample spiked with known activity of ²³⁹Pu. The results obtained for procedures were compared in terms of activities and recoveries.     

Characterization and source term assessments of radioactive particles from Marshall Islands using non-destructive analytical techniques

Six plutonium-containing particles stemming from Runit Island soil (Marshall Islands) were characterized by non-destructive analytical and microanalytical methods. Composition and elemental distribution in the particles were studied with synchrotron radiation based micro X-ray fluorescence spectrometry. Scanning electron microscope equipped with energy dispersive X-ray detector and with wavelength dispersive system as well as a secondary ion mass spectrometer were used to examine particle surfaces. Based on the elemental composition the particles were divided into two groups: particles with pure Pu matrix, and particles where the plutonium is included in Si/O-rich matrix being more heterogenously distributed. All of the particles were identified as nuclear fuel fragments of exploded weapon components. As containing plutonium with low ²⁴⁰Pu/²³⁹Pu atomic ratio, less than 0.065, which corresponds to weapons-grade plutonium or a detonation with low fission yield, the particles were identified to originate from the safety test and low-yield tests conducted in the history of Runit Island. The Si/O-rich particles contained traces of ¹³⁷Cs (^239 + 240Pu/¹³⁷Cs activity ratio higher than 2500), which indicated that a minor fission process occurred during the explosion. The average ²⁴¹Am/²³⁹Pu atomic ratio in the six particles was 3.7 × 10^− 3 ± 0.2 × 10^− 3 (February 2006), which indicated that plutonium in the different particles had similar age.     

Determination of isotopic ratios of plutonium and curium by internal conversion electron spectrometry

The isotopic ratios²⁴⁰Pu/²³⁹Pu in plutonium samples purified freshly and allowed to stand for a long time were determined by using a high resolution internal conversion electron spectrometer. As a result, it was proved that the above ratios can be determined accurately and precisely. The method was also examined further through a similar determination with curium samples.     

Calibration and use of a high-resolution,low-energy photon detector for measuring plutonium isotopic abundances

A low-energy photon detector was easily and accurately calibrated with plutonium sources of known isotopic contents after purification of the sources by anion exchange. Rapid data processing was attained by minicomputer calculations. Results obtained for plutonium abundances by λ-spectrometry and by mass spectrometry agreed within 1% for the ²⁴⁰Pu isotope, and within 10% for ²³⁸Pu and ²⁴¹Pu at the concentrations normally present. Alpha specific activities calculated from the abundances obtained by the two methods agreed within 0.5%.     

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.     

2-D analysis of Ge implanted SiO2 surfaces by laser-induced breakdown spectroscopy

2-D elemental distribution of Ge in silicon oxide substrates with differing implantation doses of between 3 × 10¹⁶ cm^− 2 and 1.5 × 10¹⁷ cm^− 2 has been investigated by Laser-Induced Breakdown Spectroscopy (LIBS). Spectral emission intensity has been optimized with respect to time, crater size, ablation depth and laser energy. Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) coupled with Energy-Dispersive X-Ray Spectroscopy (EDX) have been utilized to obtain crater depth, morphology and elemental composition of the sample material, respectively. LIBS spectral data revealed the possibility of performing 2-D distribution analysis of Ge atoms in silicon oxide substrate. EDX analysis results confirmed that LIBS is capable to detect Ge atoms at concentrations lower than 0.2% (atomic). LIBS as a fast semi-quantitative analysis method with 50 µm lateral and 800 nm depth resolution has been evaluated. Results illustrate the potential use of LIBS for rapid, on-line assessment of the quality of advanced technology materials during the manufacturing process.