Swipe Samples Research Articles

Refinement of Pu parent–daughter isotopic and concentration analysis for forensic (dating) purposes

Plutonium (Pu) metal samples from an interlaboratory exchange exercise and simulated swipe samples were dated using plutonium–uranium (Pu–U) and plutonium–americium (Pu–Am). Metal data were evaluated for consistency and the swipe data against its source material. Metal ages based on 239Pu versus 235U and 240Pu versus 236U agreed to within a few percent, while the 238Pu–234U and 241Pu–241Am measurements had larger uncertainties. Swipe ages compared favorably with the material’s known history. Neptunium (237Np) analyses were examined in the context of the 241Pu–241Am–237Np system to estimate whether Np can provide insights on material from which Am, Np, and U were removed.

Selective Detection of Particles Containing Highly Enriched Uranium for Nuclear Safeguards Environmental Samples

A method to selectively detect uranium particles with high 235U enrichment has been developed; this method can contribute to improving particle analysis on nuclear safeguards environmental samples. The newly developed method involves three key components: (1) a two-step filtration system for particle recovery from swipe samples, (2) a system for controlling the etching time of fission track (FT) detector, and (3) a system for comparing the FT morphologies and particle sizes. The method to screen uranium particles according to their enrichment is focused on detecting highly enriched uranium particles preferentially in various particles recovered from swipe sample; this is one of the most important tasks involved in nuclear safeguards. In order to verify the effectiveness of the screening method developed, a mixture sample containing uranium particles with natural composition and those with 10% enrichment is used. It was shown that enrichment-based screening of uranium particles is possible by comparing the FT morphologies and particle sizes, in addition to controlling the etching time. The developed method uses the etching behaviors of the FT detector mainly; thus, it can be applied to real swipe samples easily.

Determination of fluorine in uranium oxyfluoride particles as an indicator of particle age

As swipe samples from enrichment activities typically contain uranium particles with a detectable amount of fluorine, the question was raised whether the analysis of fluorine in particles could complement the information on the uranium isotope ratios. For this, uranium oxyfluoride particles were prepared from the controlled hydrolysis of uranium hexafluoride (UF 6). The relative amount of fluorine was characterized by scanning electron microscopy combined with energy-dispersive X-ray spectrometry (SEM-EDX), as well as ion-microprobe secondary ion mass spectrometry (IM-SIMS). Of particular interest was the assessment of the reduction of the amount of fluorine over time, and after exposure to UV-light and high temperatures. Micro-Raman spectrometry (MRS) was applied to look for differences in molecular structure between these various sample types. Both SEM-EDX and IM-SIMS showed a general reduction of the fluorine-to-uranium ratio after 1–2 years of storage. The exposure to UV-light and high temperatures was found to have accelerated the loss of fluorine. A distinct peak at 865 cm − 1 Raman shift was detected for the majority of particles analyzed by MRS. For the particles that were heat-treated, the Raman spectra were similar to the spectrum of U 3O 8. Although often large variations were observed between particles from the same sample, the three particle measurement techniques (IM-SIMS, SEM-EDX and MRS) showed some consistent trends. They therefore appear promising in terms of the ability to place bounds on particle age, as well as shedding light on the complex processes involved in UO 2F 2 particle ageing.

Comparison of ICP-MS and SIMS techniques for determining uranium isotope ratios in individual particles

The determination of uranium isotope ratios in individual particles is of great importance for nuclear safeguards. In the present study, an analytical technique by inductively coupled plasma mass spectrometry (ICP-MS) with a desolvation sample introduction system was applied to isotope ratio analysis of individual uranium particles. In ICP-MS analysis of individual uranium particles with diameters ranging from 0.6 to 4.2 μm in a standard reference material (NBL CRM U050), the use of the desolvation system for sample introduction improved the precision of 234U/ 238U and 236U/ 238U isotope ratios. The performance of ICP-MS with desolvation was compared with that of a conventionally used method, i.e., secondary ion mass spectrometry (SIMS). The analysis of test swipe samples taken at nuclear facilities implied that the performance of ICP-MS with desolvation was superior to that of SIMS in a viewpoint of accuracy, because the problems of agglomeration of uranium particles and molecular ion interferences by other elements could be avoided. These results indicated that ICP-MS with desolvation has an enough ability to become an effective tool for nuclear safeguards.

Microscopic studies of spherical particles for nuclear safeguards

A combination of micro-analytical techniques was used for the characterization of spherical particles in the size range 9–12 μm as a part of nuclear safeguards verification activities pursuant to the Treaty on the Non-Proliferation of Nuclear Weapons (NPT). The particles were removed from cotton swipe samples taken in a nuclear facility under safeguards and examined first by scanning electron microscopy combined with energy-dispersive X-ray spectrometry (SEM–EDX). Particles of interest were then relocated under an optical microscope and manipulated. One such particle was subjected to destructive analysis by secondary ion mass spectrometry (SIMS) in order to determine if uranium was present in the core of the particle. A second particle was examined using focused ion beam (FIB) etching to allow an examination of the interior by SEM–EDX. The particle manipulation and relocation techniques presented here allow the sequential examination of a single particle of interest by a combination of analytical techniques, thus yielding surface morphological, elemental, isotopic and depth-profiling information. The objective of these investigations is to provide assurance of the absence of clandestine or undeclared nuclear activities in States coming under comprehensive safeguards obligations.

Study on analysis of isotopic ratio of uranium-bearing particle in swipe samples by FT-TIMS

A fission track (FT) technique has been developed for searching for, locating and transferring a single uranium-bearing particle from swipe samples. The technique consists of (1) searching for uranium-bearing particles in swipe samples by FT technique; (2) locating the particle by FT cluster under optical microscope and (3) transferring the particle from the swipe sample to a filament (Re) of TIMS. The study shows that the efficiency of searching for uranium-bearing particles reaches 90% for particles of size 0.5 – 20 μ m with proper concentration of uranium; the accuracy of locating particles is better than 5 μ m ; and the transference efficiencies of particles from swipes to Re filaments are ∼ 90 % , ∼ 73 % and ∼ 43 % for particle sizes 0.5–5, 5–10 and 10 – 20 μ m , respectively. Analysis of U 235 and U 238 isotopic abundances in the particles by TIMS shows that the isotopic abundances are in agreement with those of original reference materials. The study shows that the FT technique combined with TIMS is a feasible, easy-managing and accurate method for determination of uranium isotopes of a single microscopic particle.

Application of ICP-QMS for the determination of plutonium in environmental samples for safeguards purposes

Aiming to determine the plutonium amount as well as its isotopic composition, in particular, in swipe samples for safeguards purposes, an analytical method was developed with a plutonium separation step based on extraction chromatography using 2 cm TEVA columns and detection with quadrupole ICP-MS applying an ultra-sonic nebulizer coupled with membrane desolvation system. The method was successfully applied to New Brunswick plutonium certified reference materials as well as to Lawrence Livermore National Laboratory round robin samples, based on the round robin samples provided by the Institute for Reference Materials and Measurements (Belgium), as part of the Regular European Interlaboratory Measurement Evaluation Programme (REIMEP), campaign 16 (isotopic abundances of plutonium in plutonium nitrate samples), with a total plutonium amount between 1 and 0.25 ng per sample. After the introduction of an additional separation step, it was also possible to carry out precise and accurate total plutonium, 240Pu/ 239Pu, 241Pu/ 239Pu and 242Pu/ 239Pu atom ratios determination in sediment sample showing its applicability to environmental samples in general, reaching a detection limit equivalent to 5 mBq 239Pu kg −1.

Particle isolation for analysis of uranium minor isotopes in individual particles by secondary ion mass spectrometry

A new technique to measure 234U/ 238U and 236U/ 238U isotope ratios for individual particles in environmental samples was developed, which was a combination of particle isolation under scanning electron microscope (SEM) and secondary ion mass spectrometry (SIMS). The technique was verified by measuring 234U/ 238U and 236U/ 238U isotope ratios in individual particles in a simulated environmental sample containing uranium standard (NBL CRM U010) and Pb metal particles. When the uranium particles were not isolated, the relative deviations of the measured isotope ratios from the reference values increased with increasing the signal intensity ratio of 208Pb to 238U, which was due to the molecular ion interferences by the Pb particles co-existing in the sputtered area. By the isolation of individual uranium particles, the interferences were eliminated and the measured isotope ratios were in good agreement with the reference values. The maximum relative deviations among 20 particles were 8.9% for 234U/ 238U and 13.1% for 236U/ 238U isotope ratios, respectively. The technique was also successfully applied to the analysis of a real swipe sample containing various kinds of elements.

The preparation of uranium-adsorbed silica particles as a reference material for the fission track analysis

Uranium-adsorbed silica particles were prepared as a reference material for the fission track analysis (FTA) of swipe samples. A modified instrumental setup for particle generation, based on a commercial vibrating orifice aerosol generator to produce various sizes of droplets from a SiO 2 solution, is described. The droplets were transferred into a weak acidic solution bath to produce spherical solid silica particles. The classification of the silica particles in the range from 5 to 20 μm was carried out by the gravitational sedimentation method. The size distribution and morphology of the classified silica particles were investigated by scanning electron microscopy. The physicochemical properties of the classified silica particles such as the surface area, pore size and pore volume were measured. After an adsorption of 5% 235U on the silica particles in a solution adjusted to pH 4.5, the uranium-adsorbed silica particles were calcined up to 950 °C in a furnace to fix the uranium strongly onto the silica particles. The various sizes of uranium-adsorbed silica particles were applied to the FTA for use as a reference material.

Efficient Isotope Ratio Analysis of Uranium Particles in Swipe Samples by Total-Reflection X-ray Fluorescence Spectrometry and Secondary Ion Mass Spectrometry

A new particle recovery method and a sensitive screening method were developed for subsequent isotope ratio analysis of uranium particles in safeguards swipe samples. The particles in the swipe sample were recovered onto a carrier by means of vacuum suction-impact collection method. When grease coating was applied to the carrier, the recovery efficiency was improved to 48±9%, which is superior to that of conventionally-used ultrasoneration method. Prior to isotope ratio analysis with secondary ion mass spectrometry (SIMS), total reflection X-ray fluorescence spectrometry (TXRF) was applied to screen the sample for the presence of uranium particles. By the use of Si carriers in TXRF analysis, the detection limit of 22 pg was achieved for uranium. By combining these methods with SIMS, the isotope ratios of 235U/238U for individual uranium particles were efficiently determined.

Feasibility study of solid sampling electrothermal vaporization inductively coupled plasma mass spectrometry for the determination of particulate uranium in swipe samples from nuclear facilities

The feasibility of a solid sampling electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) for “the particle analysis of safeguards environmental swipe samples” was studied with polycarbonate (PC) film samples containing thallium (Tl), lead (Pb) and uranium (U) particles in single element and with their solution sample. The influences of instrumental operating conditions on analytical results, especially accuracy and precision in isotope ratio measurements, were investigated. Isotope ratios obtained for Tl and Pb solution samples containing a few picogram amounts of particles were in good agreement with the reference values obtained using pneumatic nebulizer ICP-MS. It is revealed that when vaporization temperature was set to be optimal, the pyrolysis temperatures in the temperature range of this study did not affect the magnitude of integrated signals. Isotope ratios obtained for PC film samples including a few picogram amounts of particles were comparable to those of solution samples, and good values of isotope ratio were obtained in the wide range of measurement parameters even though analyte losses occurred in inappropriate temperature conditions. The pyrolysis and vaporization temperature dependence of the integrated signal was different from those of the solution sample, which is ascribed to the difference of transport efficiency of the vaporized analyte in both samples. Absolute limit of detection for PC film sample was found to be about 2 fg, which corresponds to 2 pg/g for a typical sample mass of 1 mg.

Efficient Isotope Ratio Analysis of Uranium Particles in Swipe Samples by Total-Reflection X-ray Fluorescence Spectrometry and Secondary Ion Mass Spectrometry

Efficient Isotope Ratio Analysis of Uranium Particles in Swipe Samples by Total-Reflection X-ray Fluorescence Spectrometry and Secondary Ion Mass Spectrometry

Studies on treatment methods of the safeguards swipe samples for uranium isotope ratio measurement

In the environmental sampling and analyses for safeguards, precise and accurate isotope ratio determination of uranium at trace levels is required for detection of undeclared nuclear activities. Currently, swipe (smear) samples are being taken by IAEA from the nuclear facilities. The amount of uranium collected on the cotton swipe is expected to be in the wide range including the order of nano-gram or less. In order to measure the isotope ratios by ICP-MS, we have studied sample preparation procedures for the trace amount of uranium. Elements causing spectroscopic and non-spectroscopic interferences in ICP-MS measurement were sufficiently removed by anion-exchange of hydrochloric acid media. The uranium contamination introduced throughout the process of sample preparation was below 10 pg uranium per sample. The applicability of the treatment process for uranium isotope measurement up to 100 pico-grams was proposed.

Characterisation of environmental radioactive particles

Control samples produced as 1pm size uranium oxide particles are described for the calibration of the instrumental techniques when applied for the characterisation of environmental radioactive particles. The efficiency of nuclear track methods is demonstrated for the location of hot spots in swipe and environmental samples. Examples of the characterisation in terms of morphology, structure, elemental and isotopic composition of radioactive environmental particles detected in sediments and soil samples from different origin are illustrated. The characteristics of the particles are related with the source term and the release scenarios. Correlation between measurements of bulk samples and particles are given.

SCREENING OF URANIUM PARTICLES BY TOTAL-REFLECTION X-RAY FLUORESCENCE SPECTROMETRY FOR SAFEGUARDS ENVIRONMENTAL SAMPLE ANALYSIS

The capability of total-reflection X-ray fluorescence spectrometry (TXRF) technique was studied to screen a swipe sample for uranium content, which was employed to decide on the further isotopic ratio measurements by secondary ion mass spectrometry (SIMS) for safeguards environmental sample analysis. A part of the measurement system of TXRF was modified to be able to use the same glassy carbon carrier for SIMS analysis. Particles in the swipe sample were recovered on the carbon carrier. The relative sensitivities of 11 elements including uranium were determined using selenium as an internal standard. The detection limit of uranium was 0.4 ng. The screening technique studied was applied to the practical swipe samples taken from the laboratories. The results confirm that TXRF can be a promising screening technique for uranium in swipe samples for safeguards environmental sample analysis.

Radioactive particle analysis by digital autoradiography.

We have been exploring ways to evaluate the activity of radioactive particles that have been detected by phosphor plate digital autoradiography based on photostimulated luminescence (PSL). A PSL system with 25 μm pixel digitization has been applied to particle analysis problems, both qualitatively and quantitatively. Two data evaluation methods are currently employed: (1) bulk area signal measurement, and (2) discrete event counting which may include spectral evaluation. The first method is conventional, whereas the second method requires high spatial resolution and is presented here for the first time. The counting methods can discriminate between alpha and background counts. The unshielded background signal accumulation rate was determined by the bulk area method. Using the spectral method of evaluation for α-particle events, the mean signal intensity per recorded α-particle was measured, and the detective quantum efficiency (DQE) was found to be nominally 100%. We present a comparison to gamma-spectrometry for sub-Bq 137Cs activities, and demonstrate an application for the qualitative assay of International Atomic Energy Agency swipe samples collected from uranium enrichment facilities.

Application of secondary ion mass spectrometry to the identification of single particles of uranium and their isotopic measurement

An instrumental method based on the use of secondary ion mass spectrometry (SIMS) is presented for the identification of uranium particles, and the determination of their isotopic composition. The particles collected on swipe samples were transferred to a special adhesive support for analysis by SIMS. Charging effects during analysis were avoided by a coating with 20 nm carbon. For the measurements of the isotope ratios a mass resolution of 1000 was sufficient. At this resolution, flat-top peaks were obtained which greatly improve the accuracy of the measurement. A detection limit in the ng/g—pg/g range was obtained by optimizing different instrumental parameters, such as the acquisition time. Blank samples, consisting only of the adhesive support and of swipes collected in an environment where uranium was absent, were employed for the evaluation of the background signals in the mass range 233–240. The level of background was eliminated by applying a voltage offset. From the results obtained on simulated swipe samples containing certified enriched uranium, the approach used was found to be very promising and after further improvements has been applied for the routine analysis of uranium particles in swipe samples.

Strengthening IAEA safeguards through environmental sampling and analysis

The IAEA conducts nuclear safeguards world-wide to verify countries' compliance with international agreements such as the Treaty on the Non-Proliferation of Nuclear Weapons (NPT). For the past 25 years, the traditional safeguards tools of materials accountancy, containment and surveillance were focused on the declared nuclear materials in a country's fuel cycle. Following events in Iraq in 1991 and elsewhere, the IAEA initiated `Programme 93+2' with the goals of strengthening the safeguards system, making it more cost-efficient and providing an enhanced ability to detect undeclared nuclear activities in States subscribing to comprehensive IAEA safeguards agreements. Environmental sampling and analysis are one important new feature introduced to aid in the detection of undeclared nuclear activities. This paper will describe the rationale behind this programme, the sampling and analytical methodology used, and the relevant quality assurance measures. The IAEA's Class-100 Clean Laboratory in Seibersdorf will be described along with the highly sensitive analytical techniques which will be employed there to determine the uranium and plutonium content and isotopic composition in environmental swipe samples collected during routine safeguards inspections. The analytical contribution of a Network of Analytical Laboratories in the Member States will also be described.

95/01450 Court indicts thermo-lag maker for conspiracy

The 2 MV tandem accelerator named ‘STAR’ was installed at ANSTO in 2003 and commissioned in 2004. It is used for ion beam analysis (IBA) and for radiocarbon measurements by accelerator mass spectrometry (AMS). Convenient space for the accelerator was found in the same building occupied by the decommissioned Argonaut-class nuclear reactor ‘Moata’; the name derives from the aboriginal word for ‘fire stick’ or ‘gentle fire’, appropriate for a 100 kW research reactor. This reactor operated between 1961 and 1995.In 2007 ANSTO’s Engineering Division assembled a team to dismantle and remove the reactor structure, along with its 12.1 tonnes of graphite reflector. The removal and remediation was completed in November 2010 and has won the team a number of prestigious awards. The entire operation was conducted inside a negatively-pressurised double-walled vinyl tent. An air curtain was positioned around the reactor core. The exhaust air from the tent passed through 2-stage HEPA filters before venting through an external stack. Neither ANSTO staff nor contractors received any significant radiation dose during the operation.Given the sensitivity of STAR for detection of 14C/12C (∼10−16) and the numerous routes for production of 14C in the reactor such as 13C(n, γ)14C, 14N(n, p)14C and 17O(n, α)14C there was the potential to directly contaminate the STAR environment with 14C. Furthermore, there was concern that reactor-14C could find its way from this building into the building where the radiocarbon sample preparation laboratories are located. This necessitated restrictions on staff movement between the buildings.We report on 14C control measurements made during and after the operation. These involved direct measurements on the reactor graphite and concrete bioshield, blank targets that were exposed in the building, swipe samples taken inside the tent and around the building and aerosol samples that were collected inside the building throughout the operation.

95/01446 ANDROS gets ready for the hot jobs

The 2 MV tandem accelerator named ‘STAR’ was installed at ANSTO in 2003 and commissioned in 2004. It is used for ion beam analysis (IBA) and for radiocarbon measurements by accelerator mass spectrometry (AMS). Convenient space for the accelerator was found in the same building occupied by the decommissioned Argonaut-class nuclear reactor ‘Moata’; the name derives from the aboriginal word for ‘fire stick’ or ‘gentle fire’, appropriate for a 100 kW research reactor. This reactor operated between 1961 and 1995.In 2007 ANSTO’s Engineering Division assembled a team to dismantle and remove the reactor structure, along with its 12.1 tonnes of graphite reflector. The removal and remediation was completed in November 2010 and has won the team a number of prestigious awards. The entire operation was conducted inside a negatively-pressurised double-walled vinyl tent. An air curtain was positioned around the reactor core. The exhaust air from the tent passed through 2-stage HEPA filters before venting through an external stack. Neither ANSTO staff nor contractors received any significant radiation dose during the operation.Given the sensitivity of STAR for detection of 14C/12C (∼10−16) and the numerous routes for production of 14C in the reactor such as 13C(n, γ)14C, 14N(n, p)14C and 17O(n, α)14C there was the potential to directly contaminate the STAR environment with 14C. Furthermore, there was concern that reactor-14C could find its way from this building into the building where the radiocarbon sample preparation laboratories are located. This necessitated restrictions on staff movement between the buildings.We report on 14C control measurements made during and after the operation. These involved direct measurements on the reactor graphite and concrete bioshield, blank targets that were exposed in the building, swipe samples taken inside the tent and around the building and aerosol samples that were collected inside the building throughout the operation.