NUSIMEP-7: Uranium isotope amount ratios in uranium particles

The Additional Protocol (AP) authorizes safeguards authorities to verify the absence of undeclared nuclear activities in all parts of a state’s nuclear fuel cycle as well as any other location where nuclear material is or may be present. As part of the Additional Protocol, environmental sampling has become an important tool for the detection of non-declared nuclear activities. In environmental sampling micrometer-sized uranium particles with an isotopic composition characteristic for the processes at the inspected facility need to be collected, identified and analysed. Considering the potential consequences of the analyses, these measurements need to be subjected to a rigorous quality management system. NUSIMEP-7 focused on measurements of uranium isotope amount ratios in uranium particles aiming to support laboratories involved in uranium particle analysis. It was the second NUSIMEP on particle analysis coordinated by IRMM. NUSIMEP-7 was open for participation to all laboratories in the field of particle analysis, particularly also to the IAEA network of analytical laboratories for environmental sampling (NWAL). The NUSIMEP test samples were prepared by controlled hydrolysis of well certified uranium hexafluoride. Participating laboratories in NUSIMEP-7 received the test samples of uranium particles on two graphite disks with undisclosed isotope amount ratio values n(234U)/n(238U), n(235U)/n(238U) and n(236U)/n(238U). The uranium isotope amount ratios had to be measured using their routine analytical procedures. Measurement of the major ratio n(235U)/n(238U) was obligatory; measurement of the minor ratios n(234U)/n(238U) and n(236U)/n(238U) were optional. 24 institutes registered for NUSIMEP-7, whereof 17 have reported measurement results using different analytical methods, among those were 7 NWAL laboratories. The participants’ measurement results have been evaluated against the certified reference values in compliance with ISO 13528:2005. The results of NUSIMEP-7 confirm the capability of laboratories in measuring n(234U)/n(238U), n(235U)/n(238U) and n(236U)/n(238U) in uranium particles of <1 µm. Furthermore they underpin the recent advances in instrumental techniques in the field of particle analysis. In addition feedback from the measurement communities from nuclear safeguards, nuclear security and earth sciences was collected in view of identifying future needs for NUSIMEP interlaboratory comparisons.JRC.D.2-Reference material

Development of Uranium Reference Particles to Support Nuclear Safeguards

Controlled hydrolysis of certified uranium hexafluoride, carried out in a specifically constructed aerosol chamber, leads to the production of uranyl fluoride particulates which ¿deposited on a graphite planchet support ¿ may be used as a quality control reference material. The particle size and surface distribution depends on several parameters, such as relative humidity inside the aerosol chamber and the concentration of gaseous uranium hexafluoride, determined by the distillation conditions. The best quality samples were obtained a RH ranging from 55 to 70% and low gas amount. These improvements for a single deposition were used to prepare a reference sample with two different uranium enrichments. Preliminary SIMS measurements proved good results with respect to both type of particles. It was also revealed that ¿ in some case ¿ the micrometer size uranium particles are accompanied by a large medium background.JRC.DG.D.2-Reference material

Structural bases of peptidoglycan recognition by lysostaphin SH3b domain.

Staphylococcus simulans lysostaphin cleaves pentaglycine cross-bridges between stem peptides in the peptidoglycan of susceptible staphylococci, including S. aureus. This enzyme consists of an N-terminal catalytic domain and a cell wall binding domain (SH3b), which anchors the protein to peptidoglycan. Although structures of SH3bs from lysostaphin are available, the binding modes of peptidoglycan to these domains are still unclear. We have solved the crystal structure of the lysostaphin SH3b domain in complex with a pentaglycine peptide representing the peptidoglycan cross-bridge. The structure identifies a groove between β1 and β2 strands as the pentaglycine binding site. The structure suggests that pentaglycine specificity of the SH3b arises partially directly by steric exclusion of Cβ atoms in the ligand and partially indirectly due to the selection of main chain conformations that are easily accessible for glycine, but not other amino acid residues. We have revealed further interactions of SH3b with the stem peptides with the support of bioinformatics tools. Based on the structural data we have attempted engineering of the domain specificity and have investigated the relevance of the introduced substitutions on the domain binding and specificity, also in the contexts of the mature lysostaphin and of its bacteriolytic activity

Identification of nanomaterials through measurements

This report addresses identification of nanomaterials according to the European Commission's Recommendation on the definition of nanomaterial (2011/696/EU) by measurements and discusses options and points to consider when assessing whether a particulate material is a nanomaterial or not. The primary criterion to identify nanomaterials is the median of the number-based distribution of the constituent particles’ external dimensions, regardless of whether these particles appear separate from one another or are parts of aggregates or agglomerates. The main steps in the nanomaterial identification process are collecting information on the material, acquiring knowledge of the measurement method(s), matching method(s) and material, sample preparation, measurement/analysis and decision (nanomaterial / no nanomaterial). Assessment of particle size measurements requires specification of the measurand, the physical principle of the measurement technique, the applied sample preparation protocol, the covered size range and the data analysis procedure to allow a reliable classification of a material according to the EC nanomaterial definition. A variety of screening and confirmatory techniques is available to analyse particle size distributions. Screening techniques do not measure directly the number-based distribution of the external particle dimensions, but they are fast and inexpensive and still allow to positively identify a material as a nanomaterial. Confirmatory techniques are usually more costly and time-intensive, but may provide a more reliable classification and allow resolving doubts or disputes. The volume specific surface area can serve as proxy to identify nanomaterials, provided that certain requirements are fulfilled. For a correct classification whether a material is a nanomaterial or not, a thorough knowledge of the applied measurement method is needed to correctly interpret the outcome of a measurement and to understand whether a specific technique is fit for the purpose. Reliable measurement results can be obtained if a reference measurement system is implemented, which is typically based on documented and validated methods and reference materials. Best practices should be applied when reference measurement systems are not available. This report provides examples and practical options for consideration, including a flowchart that can assist users with relevant technical knowledge in the identification of nanomaterials.JRC.F.2-Consumer Products Safet

NUSIMEP-7: uranium isotope amount ratios in uranium particles

The Institute for Reference Materials and Measurements (IRMM) has extensive experience in the development of isotopic reference materials and the organization of interlaboratory comparisons (ILC) for nuclear measurements in compliance with the respective international guidelines (ISO Guide 34:2009 and ISO/IEC 17043:2010). The IRMM Nuclear Signatures Interlaboratory Measurement Evaluation Program (NUSIMEP) is an external quality control program with the objective of providing materials for measurements of trace amounts of nuclear materials in environmental matrices. Measurements of the isotopic ratios of the elements uranium and plutonium in small amounts, typical of those found in environmental samples, are required for nuclear safeguards and security, for the control of environmental contamination and for the detection of nuclear proliferation. The measurement results of participants in NUSIMEP are evaluated according to international guidelines in comparison to independent external certified reference values with demonstrated metrological traceability and uncertainty. NUSIMEP-7 focused on measurements of uranium isotope amount ratios in uranium particles aiming to support European Safeguards Directorate General for Energy (DG ENER), the International Atomic Energy Agency’s (IAEA) network of analytical laboratories for environmental sampling (NWAL) and laboratories in the field of particle analysis. Each participant was provided two certified test samples: one with single and one with double isotopic enrichment. These NUSIMEP test samples were prepared by controlled hydrolysis of certified uranium hexafluoride in a specially designed aerosol deposition chamber at IRMM. Laboratories participating in NUSIMEP-7 received the test samples of uranium particles on two graphite disks with undisclosed isotopic ratio values n(234U)/n(238U), n(235U)/n(238U) and n(236U)/n(238U). The uranium isotope ratios had to be measured using their routine analytical procedures. Measurement of the major ratio n(235U)/n(238U) was obligatory; measurement of the minor ratios n(234U)/n(238U) and n(236U)/n(238U) was optional. Of the twenty-four institutes that registered for NUSIMEP-7, 17 have reported their results achieved by different analytical methods. The results of NUSIMEP-7 confirm the capability of laboratories in measuring n(234U)/n(238U), n(235U)/n(238U) and n(236U)/n(238U) in uranium particles of the size below 1 mm diameter. Furthermore, they underpin the recent advances in instrumental techniques in the field of particle analysis. In addition, feedback from the measurement communities from nuclear safeguards, nuclear security and earth sciences was collected in view of identifying future needs for NUSIMEP interlaboratory comparisons.JRC.D.2-Standards for Innovation and sustainable Developmen

Physicochemical Study of 'Dolomitic' Sorbents Prepared under Different Thermal Conditions. Part I. The Influence of Temperature

The partial decomposition of dolomite performed within the temperature range 800-1000°C provides new sorbents, the so-called 'dolomitic' sorbents, composed of calcite and magnesium oxide. Their surface properties, such as their porosity and adsorption capabilities towards hydrocarbons, are discussed. The 'dolomitic' sorbents show a much higher specific surface area and pore volume when compared to the raw dolomite; moreover, their porous structure depends on the temperature of heating. The adsorption of selected hydrocarbons on the examined sorbents was also investigated and the adsorption energy distribution functions calculated from the adsorption data

Physicochemical Study of 'Dolomitic' Sorbents Prepared under Different Thermal Conditions. Part II. Sintering as a Result of Long-term Heating

The influence of prolonged heating (12,24 and 46 h) on the porous structure and surface properties of 'dolomitic' sorbents was investigated. No important changes in the specific surface areas were found. However, increasing the heating time resulted in a decrease in the total pore volume and the average pore radius as well as considerable differences in the pore size distributions. These changes may be explained by the effect of sintering which accompanies many gas-solid reactions. The adsorption properties of the sorbents towards hydrocarbons were also investigated and the adsorption energy distribution functions calculated. The investigated surfaces appeared to be strongly heterogeneous

Micro-Raman Spectroscopy of Uranium Oxyfluoride Particulate Material for Nuclear Safeguards

Environmental samples collected by safeguards organizations such as IAEA often contain particles of uranium oxyfluoride. UO2F2 is a compound formed from the hydrolysis of uranium hexafluoride. In order to investigate its changes in the environment, uranium oxyfluoride particulate material was measured by micro-Raman spectroscopy. The uranyl symmetric stretching frequency was detected in the majority of the spectra. Depending on the conditions under which the particles were prepared and stored, additional peaks and features appeared in the spectrum. Experiments were carried out using different incident laser wavelengths at the lowest possible power setting, as the particles appeared to be very heat-sensitive.JRC.DG.D.2-Reference material

In-SEM Raman microspectroscopy coupled with EDX – a case study of uranium reference particles

Information about the molecular composition of airborne uranium-bearing particles may be useful as an additional tool for nuclear safeguards. In order to combine the detection of micrometer-sized particles with the analysis of their molecular forms, we used a hybrid system enabling Raman microanalysis in high vacuum inside a SEM chamber (SEM-SCA system). The first step involved an automatic scan of a sample to detect and save coordinates of uranium particles, along with X-ray microanalysis. In the second phase, the detected particles were relocated in a white light image and subjected to Raman microanalysis. The consecutive measurements by the two beams showed exceptional fragility of uranium particles, leading to their ultimate damage and change of uranium oxidation state. We used uranium reference particles prepared by hydrolysis of uranium hexafluoride to test the reliability of the Raman measurements inside the high vacuum. The results achieved by the hybrid system were verified by using a standalone Raman microspectrometer. When deposited on exceptionally smooth substrates, uranyl fluoride particles smaller than 1000 nm could successfully be analyzed with the SEM-SCA system.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

Combined SEM/EDX and micro-Raman spectroscopy analysis of uranium minerals from a former uranium mine

Samples of the secondary uranium minerals collected in the abandoned uranium mine at Pecs (Hungary) were investigated by two micro-techniques: scanning electron microscopy (SEM/EDX) and micro-Raman spectroscopy (MRS). They were applied to locate U-rich particles and identify the chemical form and oxidation state of the uranium compounds. The most abundant mineral was a K and/or Na uranyl sulphate (zippeite group). U(VI) was also present in the form of a trioxide; evidently in much lower content.than sulphate. Few particles with U3O8 and uraninite (primary mineral exploited formerly in this mine) were also detected. This research has shown the successful application of micro-Raman spectroscopy for the identification of uranyl mineral species on the level of individual particles