Nuclear Microanalysis Research Articles

Studying distribution of gaseous impurities and carbon in titanium alloys using nuclear microanalysis

The mechanism of the formation and modification of macrodefects containing atoms of light elements upon melting and thermal and mechanical treatment of titanium alloys has been studied. To this end, an approach based on the investigation of the concentration distribution of oxygen, nitrogen, and carbon in the zone of a macrodefect using nuclear microanalysis with a locality of measurements over the sample surface to about 90 μm has been used. It has been established that a decrease in the concentration of carbon in tungstencarbide-based macrodefects upon alloy melting occurs according to the diffusion mechanism. The same mechanism is characteristic of the process of dissolution of defects of deformation origin, such as titanium oxynitrides, upon solid-state heat treatment.

Application of ion beams in materials science of radioactive waste forms: focus on the performance of spent nuclear fuel

Ion beam techniques provide unique tools for the qualification of radioactive waste forms. They address three major issues: (i) the simulation by ion irradiation of the stability of a matrix submitted to radiative environment; (ii) the doping of a material with stable or radioactive elements which simulate the species to be confined; (iii) the characterisation of a material via nuclear microanalysis techniques. Among various classes of nuclear matrices the spent nuclear fuel is widely considered as a potential candidate for the stabilisation of radioactive wastes in scenarios of long term interim storage or final geological disposal. Illustrative examples revealing the potentialities of the use of ion beams either as a pure characterisation tool – to investigate the chemical stability of the UO2 matrix under an oxygen potential – or in a combined way (e.g. irradiation/characterisation, doping/characterisation) – to explore the radiation stability and the behaviour of foreign species – are presented. Transformations (stoichiometry, depth and structure of growing hyperstoichiometric U4O9/U3O7 oxides) occurring during low-temperature air oxidation of uranium dioxide single crystals are reported. Swift heavy ion irradiation of UO2 single crystals leads to a peculiar single crystal–polycrystal transformation (i.e. polygonisation of the fluorite-type structure of the material). Irradiation of UO2 at low energy shows that the damage production is directly linked to the energy deposited in nuclear elastic collisions. The lattice location of helium atoms (generated in large amount during the storage period) in interstitial octahedral positions is discussed.

Spectroscopic study using FTIR, Raman, XPS and NEXAFS of carbon nitride thin films deposited by RF magnetron sputtering

The spectroscopic study of a-CN x thin films deposited by R.F. magnetron sputtering is reported. The bonding structure was determined using FTIR, Raman Scattering, NEXAFS and XPS results. The combination of the FTIR and Raman spectroscopy using the vibrational properties and the XPS and NEXAFS using the electronic properties of the materials is useful for a good description of the local structure in carbon nitride. The investigation is focused on the effect of the RF power and substrate temperature on the nitrogen surrounding in carbon nitride thin films. A good correlation is observed between the evolution of the π* electron states as calculated from NEXAFS, the evolution of the sp 2 bonding of carbon observed in XPS, and the evolution of the electrical and optical properties of the films. These results combined with FTIR and Raman analysis and the elemental composition determined by nuclear microanalysis allow to follow the evolution of the local structure with the deposition conditions in a-CN x films.

On the use of ion beams for the selection of radioactive waste matrices

The safe and long-term control of radioactive waste arising from nuclear power plants is one of the major challenges to the future use of nuclear energy. The evaluation of nuclear waste matrices relies on numerous conditions regarding the physico-chemical properties of the selected materials, such as resistance against oxidation or aqueous corrosion, stability in a radioactive environment, and ability to confine radioactive elements. Ion beams provide efficient tools for the evaluation of radwaste matrices since they allow to address three major issues: (i) the simulation of ion irradiation; (ii) the doping of the matrix with stable elements simulating the nuclei to be confined; and (iii) the characterization of the material by the use of nuclear microanalysis techniques. Illustrative examples are provided in the case of urania and zirconia.

Dinophysis blooms in the deep euphotic zone of the Baltic Sea: do they grow in the dark?

In situ growth rates of the toxin-producing dinoflagellate Dinophysis norvegica collected in the central Baltic Sea were estimated during the summers of 1998 and 1999. Flow cytometric measurements of the DNA cell cycle of D. norvegica yielded specific growth rates ( μ) ranging between 0.1 and 0.4 per day, with the highest growth rates in stratified populations situated at 15–20 m depth. Carbon uptake rates, measured using 14 C incubations followed by single-cell isolation, at irradiances corresponding to depths of maximum cell abundance were sufficient to sustain growth rates of 0.1–0.2 per day. The reason for D. norvegica accumulation in the thermocline, commonly at 15–20 m depth, is thus enigmatic. Comparison of depth distributions of cells with nutrient profiles suggests that one reason could be to sequester nutrients. Measurements of single-cell nutrient status of D. norvegica, using nuclear microanalysis, revealed severe deficiency of both nitrogen and phosphorus as compared to the Redfield ratio. It is also possible that suitable prey or substrate for mixotrophic feeding is accumulating in the thermocline. The fraction of cells containing digestive vacuoles ranged from 2 to 22% in the studied populations. Infection by the parasitic dinoflagellate Amoebophrya sp. was observed in D. norvegica in all samples analysed. The frequency of infected cells ranged from 1 to 3% of the population as diel averages, ranging from 0.2 to 6% between individual samples. No temporal trends in infection frequency were detected. Estimated loss rates based on observed infection frequencies were 0.5–2% of the D. norvegica population daily, suggesting that these parasites were not a major loss factor for D. norvegica during the periods of study.

Determination of the Oxygen Diffusion Coeficient in Polycrystalline Li-Ti Ferrites

Two independent methods, the isotope method based on nuclear microanalysis and the method based on measuring the electronic-conductivity activation energy, are used to determine the grain-boundary diffusion and volume diffusion of an oxygen isotope 18O in a polycrystalline lithium-titanium ferrite at the thermal annealing temperature 1073 K. A comparative analysis is conducted of the potential of the methods in studying oxygen diffusion in the material concerned. It is shown that the technique for obtaining the diffusion parameters from the electronic conductivity measurements allows a comparatively precise determination of both the volume and grain-boundary diffusion coefficients of oxygen in polycrystalline ferrites.

Application of ion beams to nuclear waste issues:: evaluation of nuclear ceramics

Oxide ceramics are promising matrices for nuclear waste immobilization or transmutation. The most important issue concerning these materials is the investigation of their physico-chemical properties with respect to safety criteria. This paper shows the potentiality of ion beams for the evaluation of ceramics as nuclear waste matrices. Several items are concerned. The different sources of radiation damage occurring in the reactor and during the storage term may be simulated by irradiation of the matrix with a variety of ions in a wide energy range. The doping of the material with foreign species produced by radioactive desintegration may be performed by ion implantation of stable or radioactive isotopes. The modifications induced in the matrices may be characterized by nuclear microanalysis techniques using medium-energy light ion beams. Examples relative to these various items are provided.

Behaviour of lanthanide aluminosilicate glass in water: Preliminary results

Lanthanide aluminosilicate glasses have been developed for their high mechanical properties. Nevertheless, little is known about their chemical durability and the role of rare-earth elements on the dissolution mechanisms of such glasses. This type of glass appears to be a suitable complement waste forms of borosilicate glass for the specific immobilisation of trivalent actinides. The first part of this paper deals with the synthesis and the characterisation of glasses in the system SiO 2–Al 2O 3–Y 2O 3–Ln 2O 3 (with Ln=La or Ce) and the second part with the study of their leachability in deionised water using a reflux column at 100°C. Hydrated glass surfaces have been examined with scanning electron microscopy coupled with X-ray microanalysis and nuclear microanalysis. Leachates have been characterised by using ICP-MS and UV-visible spectrophotometry. After leaching, the formation of a surface layer slightly depleted in Si and Al and containing Y and La hydroxicarbonates and hydroxides is discussed.

Microanalysis of Light Elements by Means of a Nuclear Microprobe: Application to Boron Compounds

The nuclear microanalysis is an elemental analysis technique based on the use of the atomic and nuclear interactions of a light ion microbeam with the sample to be analyzed. Both light particles and photons (X, γ) are detected. The determination of the local stoichiometry of boron-based compounds is possible with the use of nuclear reactions. Boron and carbon mapping of YPd-based borocarbides is presented. Additional possibilities of in-depth carbon profiling are also reported.

The role of nitrogen and sulphur bearing compounds in the wettability of oil reservoir rocks: an approach with nuclear microanalysis and other related surface techniques

Oil recovery is strongly influenced by the wettability of the reservoir rock. Some constituents of the crude oil (polar compounds and heavy fractions such as asphaltenes with heteroatoms) are believed to react with the reservoir rock and to condition the local wettability. Therefore, it is important to obtain as much knowledge as possible about the characteristics of the organic matter/mineral interactions. This study is devoted to the description at the microscopic scale of the distribution of some heavy fractions of crude oil (asphaltenes) and nitrogen molecules (pyridine and pyrrole) on model minerals of sandstone reservoir rocks such as silica and clays. Nuclear microanalysis, X-Ray Photoelectron Spectroscopy and other related microscopic imaging techniques allow to study the distribution and thickness of the organic films. The respective influences of the nature of the mineral substrate and the organic matter are studied. The important role played by the nitrogen compounds in the adsorption of organic matter is emphasized.

APPLICATIONS OF NUCLEAR MICROPROBE ANALYSIS IN CANCER CELL BIOLOGY AND PHARMACOLOGY

Nuclear microprobe analysis studies in cancer cell pharmacology and biology carried out at Bordeaux-Gradignan are reported. The cellular pharmacology of two anticancer agents, cis-diammine-dichloroplatinum(II), and 4′-iodo-4′-deoxy-doxorubicin, were investigated, as well as the role of iron in neuroblastoma carcinogenesis, and chromium(III) in trans-generation carcinogenesis. Nuclear microprobe analysis, using PIXE and particle backscattering microanalysis, was able to reveal intracellular and tissue distributions of the elements under investigation. Moreover, the fully quantitative and multi-elemental character of nuclear microprobe analysis offered information on possible mechanisms of drug action, metal carcinogenesis, and interactions with endogenous trace elements in cancer cells.

Occurrence of Boron-Rich Potassic Melts in the Vulsini Volcanic District, Italy: Evidence From Melt Inclusions

Boron was analyzed by nuclear microanalysis technique, using the 11B(p, α) 8Be reaction, in potassic to highly potassic melts (Mg# [Mg 2+/(Mg 2++ Fe 2+)] > 0.70) trapped as melt inclusions in olivine (Fo 91.7–90.5) phenocrysts from the Vulsini Volcanic District (northwestern Roman Province, Italy). These data evidence unusual B concentrations from 60 to 100 ppm, up to five times higher than any documented values in primitive subduction-related magmas. The melt inclusions display variable concentrations in B, K, Sr, and F, with constant ratios between elements, for a single volcanic event, that strongly suggest variations of the extents of batch partial melting of a mantle source enriched in B, K, Sr, and F. Conversely B/K and B/Cl ratios in potassic magmas (Mg# > 0.70), as exemplified by melt inclusions in olivine (Fo > 90), are variable on the scale of the whole Roman Province. These variations cannot be explained by either fractional crystallization or differing extents of the mantle source melting alone. This is also supported by the range in Th/Ta ratios (52–10) of the whole rock samples. Variability of the B/K or B/Cl ratios cannot be related to a single-stage metasomatism event. The data indicate the possible occurrence of B-rich contaminant and/or high inputs of subducted-derived components in the mantle wedge beneath the Vulsini area, within the peculiar geodynamic setting of the northern part of the Apenninic arc. In addition, by determining boron concentrations using nuclear microanalysis involving the 11B (p, α) 8Be nuclear reaction, we have illustrated the sensitivity of the nuclear reactions in the analysis of the light elements.

Investigation of superconducting crystals by neutron scattering and nuclear microanalysis

A combination of nuclear microanalysis (ion x-ray spectral analysis, Rutherford backscattering, and nuclear reactions) with low-angle neutron diffraction in the bulk of a Y-Ba-Cu-O ceramic rod, recrystallized by zone refining, was used to determine the elemental and phase composition of the initial ceramic, the crystal, and the transition sections. The degree of local homogeneity of the medium was also determined at scales of ∼101−102 nm.

Effects of lithium-implantation on the hydrogen retention in both a-C:H and a-SiC:H materials submitted to deuterium bombardment

The hydrogen release in plasma facing materials is a challenging problem for the hydrogen recycling. The hydrogen desorption from the a-C:H and a-SiC:H materials induced by deuterium bombardment has been investigated. Prior to the deuterium bombardment, both materials were implanted with different fluences of lithium ions. Before and after each irradiation, depth profiles of H, Li and deuterium were determined by nuclear microanalysis. After deuterium bombardment, it is shown that the retention of the initial hydrogen in both materials was enhanced by increasing the total dose of the implanted Li. For the a-C:H samples, the hydrogen desorption under deuterium bombardment was strongly reduced by lithium implantation. This effect was also evidenced in a-SiC:H samples, even though it is less spectacular than in a-C:H. Also, nuclear analyses showed that the retained dose of deuterium decreases when the lithium concentration increases. This could be a result of the formation of LiH bonds which occurs to the detriment of deuterium retention in both a-C:H and a-SiC:H materials. Preliminary results of both materials exposed to TdeV tokamak discharges confirms the role of Li in hydrogen retention, already observed in deuterium bombardment exposure.

Neutron dosimetry at low and high fluences with CR-39

In the Laboratory of Nuclear Microanalysis, we have developed two techniques for neutron dosimetry; the first for low fluence, the second for high fluence. These two techniques use a Solid State Nuclear Track Detector (SSNTD): the CR-39. The low fluence technique is based on the measurement of etched tracks resulting from a neutron-proton conversion. A Monte Carlo code performs a simulation of the (n,p) collision in the detector, and a numerical computer code of latent track etching allows the evaluation of the etched track parameters. The object of this is to obtain characteristics of a neutron fluence from the measured etched track parameters. When there is a high fluence and high doses, CR-39 is unsuited for optical microscopy analysis. This is because of track overlapping which makes it impossible to carry out counting and exploitation. We have therefore developed a new method permitting the reading of samples based on the measurement of the angular distribution of coherent light (HeNe laser) transmitted through the irradiated etched SSNTD. We present these two techniques and our initial results.

Silicon self-diffusion in quartz and diopside measured by nuclear micro-analysis methods

Diffusion coefficients of silicon have been measured for synthetic quartz and natural diopside, using two micro-analysis techniques, Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis (NRA). Diffusion experiments on quartz have been performed between 1350°C and 1600°C for durations of a few days to a few minutes, at high pressure (2 GPa) in the β-quartz field, as well as at atmospheric pressure on metastable β-quartz. Both experiments give approximately the same results and no pressure effect on silicon diffusion is observed. We find the following diffusion coefficient for silicon in synthetic quartz: (cm 2s −) =2.9 × 10 7exp −746kJ mol −1 RT In the case of diopside, we have used a natural gem-quality single crystal. Annealings were performed between 1040°C and 1250°C for durations ranging from 1 month to 6 days under controlled atmosphere. From these preliminary results, we obtain (cm 2s −) =2.3 × 10 −10exp −211kJ mol −1 RT which is not corrected for an eventual pO 2 dependence. On the basis of our results, we propose an interstitial diffusion mechanism for silicon atoms in quartz based on Frenkel pairs of defects, and we suggest also the possibility of such an interstitial mechanism occurring in diopside.

18O isotopic tracer studies of the laser ablation of Bi2Sr2Ca1Cu2O8

The mechanisms of oxygen incorporation into the growing film during the pulsed laser ablation of a Bi2Sr2Ca1Cu2O8 target have been investigated by the complementary use of 18O isotopic tracing techniques and nuclear microanalysis. Roughly 45% of the oxygen present in the film comes from the ambient gas and the remaining part is directly incorporated from the target. Moreover, oxygen is only incorporated in the Bi2Sr2Ca2Cu1O8 films during the growth period (i.e., laser pulse), since neither oxidation nor oxygen exchange occur during the time interval between successive laser pulses. It is also shown that the main mechanism of oxygen incorporation corresponds to the dissociation of molecular oxygen adsorbed at the surface, leading to the formation of very reactive atomic oxygen which is further injected in the films. This oxygen dissociation is the result of the interaction with the high flux of species coming from the target and reaching the film surface during each laser ablation pulse.

Thermal nitridation of p-type porous silicon in ammonia

The effect of nitridation at 1 000 °C in ammonia on porous silicon photoluminescence was studied. These investigations correlated the composition, the paramagnetic defects and the photoluminescence intensity. The composition of the porous layers was determined using nuclear microanalysis and Fourier transform infrared spectroscopy at 8 K. The paramagnetic defects were assessed by electron paramagnetic resonance. The results show that the hydrogen is removed from the SiHx species during the nitridation and that only nitrogen is incorporated in the layer, in the absence of hydrogen coming from ammonia. The paramagnetic defect concentration which increases at first due to the removal of hydrogen, decreases during further nitridation. The photoluminescence intensity is strongly correlated with the defect concentration. This passivation which is presently under studies is more stable than the passivation by hydrogen. Annealing at 600 °C does not lead to any increase of defect concentration.

Laser ablation of oxides: study of the oxygen incorporation by18O isotopic tracing techniques

The mechanisms of oxygen incorporation in the growing film, during the pulsed laser ablation of a BiSrCaCuO target, have been investigated by the complementary use of18O isotopic tracing techniques and nuclear microanalysis. During the film growth under18O ambient, we have shown that only 45% of the oxygen atoms present in the films comes from the ambient gas, the remaining part being directly transferred from the target. Moreover, the oxygen incorporation in the growing film was found to only occur during each laser pulse. Film oxidation, or exchange phenomena between oxygen atoms already fixed in the film, and those coming from the gas do not occur during time interval between laser pulses. It was also shown that the main mechanism of oxygen incorporation in the BiSrCaCuO thin films, corresponds to the dissociation of molecular oxygen adsorbed at the surface, leading to the creation of very reactive atomic oxygen which is further injected in the films. This dissociation being due to the bombardment by the incident energetic (5 to 10 eV) species coming from the target during each laser pulse.

Nuclear-physical methods for nondestructive thickness and quality control of multicomponent coatings

Heat-resistant coatings have been examined by nuclear-physical methods based on the study of oxygen and carbon migration inside the coatings at different stages of the coating application. The oxygen and carbon concentration was measured at various depths in the protective layer by nuclear microanalysis methods based on deuteron-proton transformation reactions and the aluminum concentration was measured by using protongamma ray transformation reactions.