Accurate purification age determination of individual uranium–plutonium mixed particles

Age of individual uranium–plutonium (U/Pu) mixed particles with various U/Pu atomic ratios (1–70) were determined by inductively coupled plasma mass spectrometry. Micron-sized particles were prepared from U and Pu certified reference materials. The Pu reference was stored for 4–6 years since the last purification (July 14, 2008). The Pu purification age was obtained from the ²⁴¹Am/²⁴¹Pu ratio which was calculated from the product of three measured ratios of Pu and Am isotopes in the eluted fractions. These ratios were measured by a high-resolution inductively coupled plasma mass spectrometer equipped with a desolvation system. Femto-gram to pico-gram quantities of Am, U, and Pu in a sample solution were sequentially separated on a small anion-exchange column. The ²⁴¹Am/²⁴¹Pu ratio was accurately determined by spiking pure ²⁴³Am into the sample solution. The average determined age for the particles for the five independent U/Pu ratios was in good agreement with the expected age with high accuracy (difference age 0.27 years) and high precision (standard deviation 0.44 years). The described analytical technique can serve as an effective tool for nuclear safeguards and environmental radiochemistry.

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Figure Young (4?6 y) Pu purification age of individual U/Pu mixed micron-sized reference particles for the five independent U/Pu ratios (1?70) were determined with 0.27±0.44 y difference from the expected age. Sub pico-gram quantities of Am, U and Pu were sequentially separated a small column, and their isotope ratios were accurately measured using an ICP-MS by applying the ²⁴³Am spiking technique to the analysis and correcting the impurity and the contaminations.

     

Simultaneous liquid scintillation determination of239Pu and241Am in tissue

A liquid scintillation counting method for the simultaneous determination of Pu and Am, with a two-phase cocktail, has been applied to the analysis of a tissue sample from an accidental exposure incident. The sample contained²³⁹Pu,²⁴¹Pu, and²⁴¹Am. In addition to analysis by two liquid scintillation counting techniques, analysis of the sample was performed by -spectroscopy and ZnS scintillation techniques, and the results were compared. The presence of²⁴¹Pu interfered with the liquid scintillation determination of²⁴¹Am when the two-phase cocktail was used, but the results were in agreement sufficient to be useful in determining what course of treatment, if any, might be necessary for the patient.     

Determination of241Pu by low level β-proportional counting. Application to Chernobyl fallout samples and comparison with the241Am build-up method

A chemical separation procedure is described which allows the direct determination of low²⁴¹Pu activities in environmental samples with a windowless gas-flow proportional counter. While current separation schemes based on anion exchange yield counting sources of sufficient purity for subsequent -spectrometry, for -counting of²⁴¹Pu additional purification steps are required. A combination of anion exchange from 9 mol/l HCl, LaF₃ precipitation and TTA extraction was found to be suitable even for the analysis of long-range Chernobyl fallout samples which contained interfering radionuclides with -activities at least 3 to 4 orders of magnitude higher than usually encountered. No difference is detectable between the results of the present, direct procedure and the results of the conventional indirect method based on the build-up of²⁴¹Am. Average²⁴¹Pu/^239+240Pu ratios in air and deposition samples taken at Neuherberg near Munich were 70±6 with the present procedure and 66±9 from²⁴¹Am build-up.     

Procedures to define Pu isotopic ratios characterizing a contaminated area in Palomares (Spain)

Plutonium isotopic ratios have been calculated in soils contaminated by the Palomares accident which occurred in 1966 (Almería, Southeastem Spain). Contrasted techniques have been used to determine the radionuclide activities:²³⁸Pu and^238+240Pu were analysed by -spectrometry prior purification on anion-exchange resins, the ratio²³⁹Pu/²⁴⁰Pu was estimated by -spectra deconvolution and²⁴¹Pu was directly measured by liquid scintillation counting and indirectly through quantification of in-grown²⁴¹Am from aged plutonium discs. The mean activity ratios²³⁸Pu/²³⁹Pu,²³⁹Pu/²⁴⁰Pu,²⁴¹Pu/²³⁹Pu, backdated to 1966, were 0.027±0.002 (1), 4.5±0.2 (1) and 8.2±0.8 (1), respectively, characterizing the accident of Palomares as the source term of the measured plutonium.     

Simultaneous determination of238Pu,239+240Pu,241Pu,241Am,242Cm,244Cm,89Sr,and90Sr in vegetation samples,and application to Chernobyl-fallout contaminated grass

A radiochemical procedure is described for the simultaneous determination of²³⁸Pu,^239+240Pu,²⁴¹Pu,²⁴¹Am,²⁴²Cm,²⁴⁴Cm,⁸⁹Sr, and⁹⁰Sr in vegetation samples. The method was applied for the determination of these, radionuclides in grass, collected near Munich after the fallout from the reactor accident at Chernobyl, USSR. The specific activities observed were (in Bq kg^–1 dry weight):²³⁸Pu, 0.077;^239+240Pu, 0.15;²⁴¹Pu, 3.9;²⁴¹Am, 0.031;²⁴²Cm, 3.0;²⁴⁴Cm, 0.008;⁸⁹Sr, 2000;⁹⁰Sr, 99.     

Studies of the vertical distribution of134Cs,137Cs,238Pu,239, 240Pu,241Pu,241Am and210Pb in ombrogenous mires at mid-latitudes

Six peat cores taken from three unmodified blanket and raised bogs in Ireland were sectioned and analyzed for a range of radionuclides including¹³⁴Cs,¹³⁷Cs,²³⁸Pu,²³⁹Pu,²⁴¹Am, and²¹⁰Pb.¹³⁴Cs and¹³⁷Cs were measured by high resolution gamma-spectrometry, while the transuranium nuclides were determined after chemical separation by alpha-spectrometry.²⁴¹Pu, present on the electroplated discs together with Pu(), was measured directly by low-level liquid scintillation counting. Core chronologies were established by measuring the unsupported²¹⁰Pb component using low energy photon spectrometry (LEPS). From the resulting profiles, relaxation depths and migration rates for the above mentioned radionuclides have been determined and differences in the values of these parameters interpreted.²³⁸Pu/^239,240Pu and²⁴¹Pu/^239,240Pu ratios have been examined carefully and are discussed in some detail. Finally, the contribution from Chernobyl to the total radiocaesium inventory in each core has been established using the¹³⁴Cs/¹³⁷Cs ratio observed in the initial fallout from Chernobyl.     

Combined procedure for the determination of90Sr,241Am and Pu radionuclides in soil samples

A combined procedure for sequential determination of low level activity concentrations of⁹⁰Sr,²⁴¹Am and Pu radionuclides is described. The analysis of -emitters is performed by isotope dilution -spectrometry using²⁴²Pu or²³⁶Pu and²⁴³Am tracers. Strontium-90 is analyzed by liquid scintillation counting using the double energetic windows method. The method combines the well established, procedure for Pu analysis based on anion exchange, the powerful and selective method for Sr isolation based on extraction chromatography using Sr-Spec resin and finally it includes the application of the TRU-Spec column for separation and purification of the Am fraction. The radiochemical procedure was tested using IAEA reference and intercomparison materials. Major parameters of the procedure as well as advantages and drawbacks are discussed in detail.     

Indirect determination of241Pu activity in soils using low energy photon spectrometers

Actinides activity levels deposited after the Chernobyl accident on the coastal Mediterranean area at Monaco have been recently measured (1). The values obtained are low. However, our -measurements on humic soils from the southern Alps revealed high¹³⁷Cs level contamination areas and urged us to evaluate²⁴¹Pu activity levels. The indirect determination of²⁴¹Pu was based on the -activity measurement of the²⁴¹Am in situ ingrown.     

Determination of 241Pu in marine samples using co-precipitation with rare earth fluoride and liquid scintillation spectrometry

²⁴¹Pu was measured in reference materials and marine samples using a novel method based on rare earth fluoride co-precipitation followed by liquid scintillation spectrometry (LSS). Disc sources used for -spectrometry of ²³⁸Pu and ^239+240Pu were leached with concentrated nitric acid before neodymium fluoride co-precipitation to scavenge plutonium in the lower oxidation states was carried out. After the determination of the chemical recovery by -spectrometry, the precipitate was recovered in a H₃BO₃/HNO₃ based dissolver and mixed with Packard Insta-Gel^Ò Plus cocktail before LSS. Reasonable agreement has been obtained between the results obtained using this methods and the data obtained by direct disc analysis by LSS and ICP-MS. The ²⁴¹Pu/^239+240Pu ratios were coherent with the expected origin of the Pu contaminant in the marine environment showing the validity of the method.This revised version was published online in November 2005 with corrections to the Cover Date.     

Liquid scintillation spectrometry of beta-emitters in marine samples

Liquid scintillation spectrometry has become the most widespread method for quantitative analysis of low level -emitters in environmental samples. This technique has been applied in the measurements of ²⁴¹Pu, ³H and ⁹⁰Sr in seawater and sediment samples. ²⁴¹Pu can be measured by direct analysis of an electrodeposited source using - discrimination or by extraction of electrodeposited plutonium into a liquid form compatible with scintillation cocktail. Sediment from Mururoa and Fangataufa atolls showed activities ranging from 18 to 44 Bq/kg. A sediment profile sampled around Bikini Atoll in 1997 showed ²⁴¹Pu activities ranging from 0.3 to 30 Bq/kg. ³H activities in pore water sediment from Mururoa and Fangataufa atolls were of the order of 10³ Bq/m³ which demonstrated its underground origin. ⁹⁰Sr was measured in the presence of ⁹⁰Y. The counting efficiency was 92.41.5% and the background 0.027±0.001 s^-1. The average chemical recovery for ⁹⁰Sr was 673%.     

Determination of the plutonium concentration by isotope dilution mass spectrometry using239Pu as a spike

A method is described for the determination of plutonium concentration in the presence of a bulk of other impurities by isotope dilution mass spectrometry /IDMS/ using²³⁹Pu as a spike. The method involves the addition of²³⁹Pu spike / 90 atom%/ to samples with²³⁹Pu / 70 atom%/ and vice versa. After ensuring chemical exchange between the sample and the spike isotopes, plutonium is purified by conventional anion exchange procedure in 7M HNO₃ medium.²³⁹Pu/²⁴⁰Pu atom ratio in the purified spiked sample is determined with high precision /better than 0.1%/ using a thermal ionization mass spectrometer. Concentration of plutonium in the sample is calculated from the changes in²³⁹Pu/²⁴⁰Pu atom ratio in the spiked mixture. Results obtained on different plutonium samples using²³⁹Pu as a spike are compared with those obtained by the use of²⁴²Pu spike. Precision and accuracy comparable to those achieved by using²⁴²Pu are demonstrated. The method provides an alternative in the event of non-availability of enriched²⁴²Pu or²⁴⁴Pu required in IDMS of plutonium and at the same time, offers certain advantages over the use of²⁴²Pu or²⁴⁴Pu spike.     

Determination of239,240Pu and241Am in environmental samples

An accurate and reliable method has been developed and routinely carried out for the sequential determination of^239,240Pu and²⁴¹Am in environmental samples. After suitable pretreatment.^239,240Pu and²⁴¹Am are separated from other elements by means of the anion exchange resin method. Americium-241 is purified by coprecipitation with calcium oxalate and then ion exchanged in mixed media of the mineral acid-methanol. In the analysis,²⁴²Pu (or²³⁶Pu) and²⁴⁴Cm are used as chemical yield monitors. The recoveries of the yield monitors in the analyses of some kinds of environmental samples were 7080% for plutonium and 7686% for curium. The concentration of^239,240Pu in the coastal sea water were 7.022 Bq/l and that of²⁴¹Am was 1.26.3 Bq/l. The mean concentrations of^239,240Pu in the edible parts of the marine products ranged from 0.22 to 7.4 mBq/kg · fresh and those of²⁴¹Am ranged from 0.11 to 2.6 mBq/kg · fresh.     

Plutonium and americium in the sediments off the Thule air base, Greenland

In 1968 a U.S. B-52 bomber from USA with four nuclear weapons crashed on the sea ice near the Thule air base and contaminated the surroundings. Most of contamination was recovered during the cleanup program. However, some of the plutonium still remains in the bottom sediments of the area. In 1997 an international expedition with a comprehensive sampling program was performed. A lot of sediment samples were taken with a Finnish Gemini corer. Sediment samples from 5 sampling stations, 80 samples altogether, were pretreated in Ris, Denmark, and analysed for transuranic elements at STUK, Finland. The samples were analysed primarily for Pu, but gamma-spectrometric measurements of ²⁴¹Am were also made. Generally, the Pu concentrations in the area studied were from 1 to 3 magnitudes higher than the fallout level in the Arctic sea area. None of the vertical profiles of Pu at the various stations showed a typical Pu peak originating from the accident in 1968, but the sediments were mixed down and contaminated to the depths studied (20 cm). The presence of large quantities of hot particles distorted the estimations of mean concentrations and inventories. Samples with plutonium from the accident show significant variations of nuclide ratios, ²³⁸Pu/^239,240Pu, ²⁴¹Pu/^239,240Pu and ²⁴¹Pu/²⁴¹Am. This indicates that Pu at Thule may be from more than one source of different quality.     

Age determination of plutonium using inductively coupled plasma mass spectrometry

The age of plutonium is defined as the time since the last separation of the plutonium isotopes from their daughter nuclides. In this paper, a method for age determination based on analysis of ²⁴¹Pu/²⁴¹Am and ²⁴⁰Pu/²³⁶Pu using ICP-SFMS is described. Separation of Pu and Am was performed using a solid phase extraction procedure including UTEVA, TEVA, TRU and Ln-resins. The procedure provided separation factors adequate for this purpose. Age determinations were performed on two plutonium reference solutions from the Institute for Reference Materials and Measurements, IRMM081 (²³⁹Pu) and IRMM083 (²⁴⁰Pu), on sediment from the Marshall Islands (reference material IAEA367) and on soil from the Trinity test site (Trinitite). The measured ages based on the ²⁴¹Am/²⁴¹Pu ratio corresponded well with the time since the last parent-daughter separations of all the materials. The ages derived from the ²³⁶U/²⁴⁰Pu ratio were in agreement for the IRMM materials, but for IAEA367 the determination of ²³⁶U was interfered by tailing from ²³⁸U, and for Trinitite the determined age was biased due to formation of ²³⁶U in the detonation of the “Gadget”.     

Plutonium, americium and cesium records in sediment cores from Blelham Tarn, Cumbria (UK)

²³⁸Pu, ^239-240Pu, and ²⁴¹Am were measured, by -counting after radiochemical separation, in two lake sediment cores. The profiles of these transuranics were compared to those of the fission product ¹³⁷Cs. Datation of nuclear events and data on behavior of the studied elements were deduced.     

Die Bestimmung von Uran und Plutonium im Rahmen der Ausscheidungsanalyse

Zusammenfassung Eine in der Praxis angewandte Analysenmethode zur Bestimmung von Plutonium in Harnproben wurde mit Hilfe von Tracerversuchen mit²³⁶Pu,²³³U und²⁴¹Am hinsichtlich ihrer radiochemischen Ausbeute und ihrer Trenneffizienz überprüft. Dabei zeigte sich, daß die Pu-Bestimmung mit einer Ausbeute von 95% praktisch quantitativ erfolgt. Im allgemeinen ist es nicht notwendig, vom Restgehalt an Uran, der 25% beträgt, weiter abzutrennen. Bei Uranmengen bis zu 100g U (nat.) sind die Meßproben alphaspektrometrisch zur qualitativen und zur quantitativen Auswertung geeignet. Auf diese Weise kann neben der Pu-Bestimmung aus demselben Alphaspektrum einer Harnprobe auch eine Aussage über die Isotopenzusammensetzung des Urangehaltes und eine mengenmäßige Abschätzung getroffen werden.Die Abtrennung des²⁴¹Am erfolgt dagegen vollständig. Der Restgehalt an²⁴¹Am in der durch Elektrodeposition hergestellten Pu-Meßprobe wurde mit weniger als 0,3% ermittelt und ermöglicht eine Auswertung des Alphaspektrums auch auf²³⁸Pu.Die Ergebnisse von Routinemessungen im Rahmen der Personenüberwachung zeigten einen normalen Urangehalt im Harn von <0,3g U/l und einen normalen Plutoniumgehalt von 0,05 pCi²³⁹Pu/24 h-Harn.

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The determination of uranium and flutonium in excretion analysis

Summary A routine method for the determination of Pu in urine samples was tested with tracer amounts of²³⁶Pu,²³³U and²⁴¹Am for its recovery and for efficiency of radiochemical separation. Pu recovery was 95%, uranium about 25%, which in generally does not need to be separated for-spectrometric determination of Pu. With uranium content up to 100g U_(nat.) counting sources are suitable for qualitative and quantitative evaluation of-spectra. In this way additionally information about the isotopic composition and the amount of uranium in the urine sample can be achieved from the same measurement.Separation from²⁴¹Am, however, can be assumed quantitatively. The activity of²⁴¹Am in such counting sources prepared by electrodeposition was less than 0,3% which enables evaluation of²³⁸Pu too. Results of routine determinations in personnel monitoring show normal background levels of uranium concentration in urine samples of less than 0,3g U (nat.)/l and for plutonium of 0,05 pCi²³⁹Pu/24-hr urine samples.

     

Multi-isotopic determination of plutonium (239Pu, 240Pu, 241Pu and 242Pu) in marine sediments using sector-field inductively coupled plasma mass spectrometry

Among the transuranic elements present in the environment, plutonium isotopes are mainly attached to particles, and therefore they present a great interest for the study and modelling of particle transport in the marine environment. Except in the close vicinity of industrial sources, plutonium concentration in marine sediments is very low (from 10⁻⁴ ng kg⁻¹ for ²⁴¹Pu to 10 ng kg⁻¹ for ²³⁹Pu), and therefore the measurement of ²³⁸Pu, ²³⁹Pu, ²⁴⁰Pu, ²⁴¹Pu and ²⁴²Pu in sediments at such concentration level requires the use of very sensitive techniques. Moreover, sediment matrix contains huge amounts of mineral species, uranium and organic substances that must be removed before the determination of plutonium isotopes. Hence, an efficient sample preparation step is necessary prior to analysis. Within this work, a chemical procedure for the extraction, purification and pre-concentration of plutonium from marine sediments prior to sector-field inductively coupled plasma mass spectrometry (SF-ICP-MS) analysis has been optimized. The analytical method developed yields a pre-concentrated solution of plutonium from which ²³⁸U and ²⁴¹Am have been removed, and which is suitable for the direct and simultaneous measurement of ²³⁹Pu, ²⁴⁰Pu, ²⁴¹Pu and ²⁴²Pu by SF-ICP-MS.     

Effects of Fe(III) ions on the electrodeposition of trace amounts of plutonium and americium

The electrodeposition of Pu and Am onto stainless steel discs from 3.2M ammonium chloride solution is strongly affected by the iron concentration of the electrolyte. At Fe(III) concentrations of more than 0.1mM (30 g Fe in 5 ml) only 30–40% of²³⁶Pu and 6% of²⁴¹Am can be deposited. Tracer experiments with⁵⁹Fe suggest that exchange processes take place between Fe from the surface layer of the cathode and from the electrolyte. Double tracer studies show increasing²³⁶Pu/⁵⁹Fe- and decreasing²⁴¹Am/⁵⁹Fe-ratios with increasing iron content of the electrolyte, which may be due to different sorption properties on colloidal iron hydroxides formed at pH<3.6.     

Simultaneous radiochemical determination of plutonium, strontium, uranium, and iron nuclides and application to atmospheric deposition and aerosol samples

Summary A procedure for the sequential radiochemical determination of plutonium, strontium, uranium and iron nuclides is described. The separation is carried out on a single anion exchange column. Pu(IV), U(VI) and Fe(III) are fixed on Bio Rad AG 1-X4 from 9 mol/l HCl, while the sample effluent is used for the determination of radio-strontium. Fe and U are eluted separately with 7 mol/l HNO₃, and Pu(III) is eluted with 1.2 mol/l HCl containing hydrogen peroxide. Subsequently, Pu and U are electrolysed and counted by alpha spectrometry. Radiostrontium is purified by the nitrate method and counted in a low level beta proportional counter. Fe is purified by extraction and cation exchange and ⁵⁵Fe is counted by X-ray spectrometry with a Si(Li) detector. The sample preparation and the application of the procedure to large samples, namely aerosols from 10⁵ m³ of air, and monthly deposition samples from 0.6 m² sampling area (10–100 l) are described. Chemical yields are for Pu 70±20, for Sr 80±15, for U 80–90, and for Fe 75±10%. As an example, the maximum airborne radionuclide concentrations determined with that procedure in fortnightly collected samples at Neuherberg after the Chernobyl accident were: ^239+240Pu, 2.58; ²³⁸Pu, 1.40; ²³⁸U, 0.65; ²³⁴U, 0.67; ⁹⁰Sr, 7600; and ⁵⁵Fe, 990 Bqm^–3.With appropriate changes in sample preparation, the procedure is applicable to other kinds of samples.     

Studies on the age determination of trace plutonium

An isotope dilution multicollector inductive coupled plasma mass spectrometry (ID-MC-ICP-MS) method for determining age of trace Pu through measuring ²⁴¹Pu/²⁴¹Am, ²⁴⁰Pu/²³⁶U ratio was established. At the same time, other two methods-α-spectrometry combined with MC-ICP-MS and liquid scintillator combined with α-spectrometry through measuring ²⁴¹Pu/²⁴¹Am ratio to determine the age of trace Pu were also studied. The techniques were explored for the age determination of nanogram grade Pu sample on the basis of Pu/Am, Pu/U separation. The ages of two Pu samples—one with known and the other with unknown age—were determined by the three methods. The determined ages by the three methods were all in agreement with the reference value. The established methods for determining the age of trace Pu could be adopted in the verification activities of nuclear safeguards and nuclear arms control.