Physical Characterization of Actinide Particles - A Study on Novel Techniques for Radiological and Nuclear Safeguard Investigations

This thesis presents a study of advanced analytical techniques, for the characterization of actinide particles originating from the non-peaceful use of nuclear technology and from international inspections of the nuclear fuel cycle associated with non-proliferation agreements. The thesis is based on five papers, which will be referred to by Paper I-V in the text. Individual particle analysis has several advantages over bulk analysis as it can give detailed information on elemental surface and internal compositions, elemental distributions, and compositional information. This information is valuable in tracing the source of the material, and in modelling and predicting the transport of radionuclides in the environment, for instance, in a release scenario. In bulk sample analysis, these characteristics are largely masked. The specific objectives of this work, which was aimed at improving the techniques used in actinide particle analysis, were: 1) the analysis of microscopic materials from nuclear weapons tests and an accidental release involving nuclear weapons (Papers I and II) and materials from nuclear inspection samples (Paper III) in order to obtain elemental and isotopic fingerprints. Single-particle analysis were performed using techniques such as secondary ion mass spectrometry (SIMS) and scanning electron microscopy (SEM) to characterize the particles, regarding elemental, isotopic, size and morphology structures, and fundamental limitations were identified; 2) the optimization of SIMS analysis of uranium particles by tuning the instrument to obtain the highest obtainable efficiency (Paper III); 3) the investigation of large-geometry SIMS applied to inspection samples to allow isotopic analysis of particles that is not possible with conventional SIMS (Paper III); 4) the production and characterization of new particle materials suitable for calibration purposes (Papers IV and V); and 5) the application of the calibration material produced for the evaluation of SIMS and SEM (Papers III and V)

Phisical Characterization of Actinide Particles. A Study on Novel Techniques for Radiological and Nuclear Safeguards Investigations

see attachmentJRC.DG.E.8-Nuclear safeguards and Securit

Human metabolism of orally administered radioactive cobalt chloride.

This study investigated the human gastrointestinal uptake (f1) and subsequent whole-body retention of orally administered inorganic radioactive cobalt. Of eight adult volunteers aged between 24 and 68 years, seven were given solutions of (57)Co (T1/2 = 272 d) containing a stable cobalt carrier, and six were given carrier-free (58)Co (T1/2 = 71 d). The administered activities ranged between 25 and 103 kBq. The observed mean f1, based on 6 days accumulated urinary excretion sampling and whole-body counting, was 0.028 ± 0.0048 for carrier-free (58)Co, and 0.016 ± 0.0021 for carrier-associated (57)Co. These values were in reasonable agreement with values reported from previous studies involving a single intake of inorganic cobalt. The time pattern of the total retention (including residual cobalt in the GI tract) included a short-term component with a biological half-time of 0.71 ± 0.03 d (average ± 1 standard error of the mean for the two nuclides), an intermediate component with a mean half-time of 32 ± 8.5 d, and a long-term component (observed in two volunteers) with half-times ranging from 80 to 720 d for the two isotopes. From the present data we conclude that for the short-lived (57)Co and (58)Co, more than 95% of the internal absorbed dose was delivered within 7 days following oral intake, with a high individual variation influenced by the transit time of the unabsorbed cobalt through the gastro-intestinal tract

Production and Characterization of Monodisperse Plutonium, Uranium, and Mixed Uranium–Plutonium Particles for Nuclear Safeguard Applications

In Safeguards work under the Non-Proliferation Treaty, the isotopic analysis of uranium and plutonium micro particles has strengthened the means for detecting undeclared nuclear activities. In order to assure accuracy and precision in the analytical methodologies used, the instrumental techniques need to be calibrated. The objective of this study was to produce and characterize particles consisting of U, Pu and mixed U–Pu, suitable for such reliability verifications. A TSI vibrating orifice aerosol generator in connection with a furnace system was used to produce micrometer sized, monodispersed particles from reference U and Pu materials in solutions. The particle masses (in the range of 3-6 pg between batches) and sizes (~1.5 μm) were controlled by the experimental conditions and the parameters for the aerosol generator. Size distributions were obtained from scanning electron microscopy, and energy-dispersive X-ray analysis confirmed that the particle composition agreed with the starting material used. A secondary ion mass spectrometer (SIMS) was used to characterize the isotopic composition of the particles. Isobaric and polyatomic interference in the SIMS spectra was identified. In order to obtain accurate estimates of the interference, a batch of Pu particles were produced of mainly 242Pu. These were used for SIMS analysis to characterize the behavior of Pu hydride and to determine the SIMS useful yields of U and Pu. It was found that Pu had a higher propensity to form the hydride than U. Useful yields were determined at a mass resolution of 450 for U–Pu particles: (1.71 ± 0.15) % for Pu and (0.72 ± 0.06) % for U, and for Pu particles: (1.65 ± 0.14) % for Pu. This gave a relative sensitivity factor between U and Pu of 2.4 ± 0.2

A biokinetic study of (209)Po in man.

Five adult volunteers participated in a biokinetic study of radioactive polonium. Portions of about 10Bq of (209)Po were orally administrated to four of the volunteers in a single ingestion. The fifth volunteer ingested a daily amount of 53mBq of 209Po for 243d to study the time to achieve equilibrium between intake and excretion for protracted intakes. For the subjects ingesting single intakes of (209)Po complete sampling of urine and feces was subsequently collected the first few days upon the ingestion. The samples were processed with radiochemical extraction and analyzed with alpha spectrometry. In the study, the maximum daily excretion rates in feces were 18-50% of the ingested activity, observed within 3d after intake. Regarding the urine excretion, the daily excretion peaked, on average, at 0.15-1% of the ingested activity within two days upon intake. These results indicate an average gastro-intestinal uptake fraction of 0.46±0.08, which agrees well with earlier biokinetic studies of polonium in man

Characterization of radioactive particles using non-destructive alpha spectrometry.

Spherical particles with known properties were used to demonstrate and test a novel software package known as AASIFIT, which is able to unfold complex alpha spectra. A unique feature of the program is that it uses simulated peak shapes in the fitting process. The experimental reference particles in the testing were artificially produced U particles of diameter 1.4mum and a nuclear bomb particle with a twenty-fold greater diameter, mainly composed of U and Pu dioxides. AASIFIT was used to determine the density of the U particles. In addition, the activities of (239+240)Pu and (241)Am were determined for the nuclear bomb particle and compared to earlier determinations in the literature. The results of this investigation demonstrated that the software can be used to estimate the properties of particles emitting alpha radiation. However, the composition and geometry of the investigated particles need to be known with good accuracy for reliable estimates. Furthermore, uncertainties in the stopping power data, especially for U and Pu, may have an influence on the results obtained from the software

Improved isotopic SIMS measurements of uranium particles for nuclear safeguard purposes

The isotopic analysis of particles containing sub-pg to pg levels of uranium, released from nuclear material handling, has been proven as an efficient tool for international safeguard purposes. Precise and accurate measurement of both enrichment and the minor isotopes is, however, a challenging analytical task due to the low levels of material. One of the mainstay techniques for particle measurement is Secondary Ion Mass Spectrometry (SIMS), this study evaluates the analytical benefit of an alternative in the form of large geometry SIMS (LG-SIMS), which combines high transmission with high mass resolution. We report here that LG-SIMS instruments provide a significantly better measurement quality than the small geometry SIMS as almost all isobaric background interferences are removed at a high useful ion yield. Useful yield measurements, performed on uranium oxide particles with calibrated uranium content, showed an overall useful yield of 1.2% for the LG-SIMS at a mass resolution of 3000. These improvements were then demonstrated by comparing results from actual nuclear inspection samples measured on both instruments. Additional benefits include an increased ability to detect particles of interest in a dust matrix while simultaneously reducing the time of sample analysis. An evaluation on the performance of LG-SIMS compared to Thermal Ion Mass Spectrometry (TIMS) is also presented. This evaluation shows that LG-SIMS has an advantage due to its high ion yield but with a limitation in the detection limit of U-236 at higher enrichments due to the necessity for a hydrogen correction

Improved Isotopic SIMS Measurements of Uranium Particles for Nuclear Safeguard Purposes

The isotopic analysis of particles containing sub-pg to pg levels of uranium, released from nuclear material handling, has been proven as an efficient tool for international safeguard purposes. Precise and accurate measurement of both enrichment and the minor isotopes is, however, a challenging analytical task due to the low levels of material. One of the mainstay techniques for particle measurement is Secondary Ion Mass Spectrometry (SIMS), this study evaluates the analytical benefit of an alternative in the form of large geometry SIMS (LG-SIMS), which combines high transmission with high mass resolution. We report here that LG-SIMS instruments provide a significantly better measurement quality than the small geometry SIMS as almost all isobaric background interferences are removed at a high useful ion yield. Useful yield measurements, performed on uranium oxide particles with calibrated uranium content, showed an overall useful yield of 1.2% for the LG-SIMS at a mass resolution of 3000. These improvements were then demonstrated by comparing results from actual nuclear inspection samples measured on both instruments. Additional benefits include an increased ability to detect particles of interest in a dust matrix while simultaneously reducing the time of sample analysis. An evaluation on the performance of LG-SIMS compared to Thermal Ion Mass Spectrometry (TIMS) is also presented. This evaluation shows that LG-SIMS has an advantage due to its high ion yield but with a limitation in the detection limit of 236U at higher enrichments due to the necessity for a hydrogen correction.JRC.E.8-Nuclear safeguards and Securit