[en] The author gives a rather detailed overview of his research activities on the behaviour of ceramics subjected to irradiations by charged or not-charged particles. He reports the development of a new application of low incidence X ray diffraction to assess the evolutions within irradiated solids. Coupling this technique with Raman spectroscopy studies enabled the monitoring of order parameter evolution in these solids. He shows that, in some oxides, irradiation effects entail order-disorder type transitions and, more surprisingly, displacive phase transitions. From this experimental work, he developed a modelling of these phase transitions induced by irradiation. Quantitative data obtained on the evolutions of order parameters enabled these phase transitions to be explained within the frame of the thermodynamics of off-equilibrium phenomena

[en] Because of its great neutronic efficiency, the boron carbide is used for the control rods of nuclear reactors. To build a model governing the material damage under irradiation many techniques have been used: nuclear microprobe, X-rays profiles diffraction study, the Raman spectroscopy and the nuclear magnetic resonance. (A.L.B.)

[en] The optimal dose of gadolinium contrast agent in intracranial MR is not established. Higher doses may improve lesion detection and conspicuity, but the upper limit is determined by toxicity and/or the presence of signal loss from T2 effects. This evaluates higher doses of a new nonionic MR contrast agent, gadoteridol. Patients had known, enhancing intracranial metastasis. Baseline T1 and T2 images and 3 serial postinjection T1 images were obtained. At 30 minutes, 0.2 mmol/kg was injected and a T1 image obtained immediately. Lesion signal intensity measurements were normalized to a reference standard. Number of lesions, lesion conspicuity, and presence of signal loss due to T2 effects from the contrast were evaluated. Eight patients had acceptable-diagnostic-quality examinations. All showed increased lesion conspicuity with the 0.3 mmol/kg cumulative does; 3 of 8 showed new lesions, and none displayed signal loss due to T2 effects

[en] Zirconia (ZrO₂) thin films were deposited by RF magnetron sputtering on zircaloy-4 (Zy-4) substrates directly from the ZrO₂ target. These thin films, deposited at different substrate temperatures from 40 to 800 deg. C and within different times from 10 to 240 min, were investigated by Raman spectroscopy and by X-ray diffraction (XRD). A rather good agreement between the results given by the two techniques was obtained. By comparison between the Raman studies on zirconia thin films and on bulk zirconia, it is possible to conclude the following: (i) films are polycrystalline; (ii) ZrO₂ is not completely dissociated during the deposition process; (iii) the structure and phase composition of the films depend on the substrate temperature and on the deposition time, thickness and, therefore, vary as a function of the distance from the film surface

[en] Zirconia produced by the oxidation of zirconium alloys in nuclear reactors exhibits a phase transition under ionic irradiation, simulating a neutron irradiation. To understand the mechanism responsible for this irradiation driven phase transition, different kinds of projectiles were used to irradiate pure monoclinic zirconia samples. The evolution of these irradiated samples as a function of dpa has been studied using grazing X-ray diffraction. The Rietveld method has been applied on collected X-ray diffraction diagrams to study the phase produced under irradiation and the kinetics of its formation. Even at high dpa values, only the monoclinic and tetragonal phases were used to simulate X-ray diffraction diagrams. No amorphisation of zirconia was observed. The evolution of unit cells and short range strains in both phases under irradiation leads us to think that the irradiation driven transition is martensitic. Supposing that the inelastic stopping power in sub-cascades is responsible for the irradiation driven phase transition, we propose a model based on the Landau-Ginzburg effective hamiltonian to explain both the m→t transition observed under irradiation and the t→m transition measured during isochronal annealing after irradiation

[en] HfB₂, a solid poor in boron, was irradiated by thermal neutrons in an experimental reactor. Using a nuclear microprobe, we have tracked lithium atoms produced by the ¹⁰B(n,α)⁷Li reaction and compared the calculated and measured ⁷Li profiles in HfB₂ irradiated samples. This comparison shows that Li atoms do not diffuse during irradiation (323 K). The comparison of non-annealed and annealed irradiated HfB₂ plates clearly shows that lithium atoms do not migrate out of samples even at high temperatures (1273 K). These results associated to previous transmission electron microscopy (TEM) observations seem to show that lithium atoms are trapped by dislocation loops created by displacement cascades during neutron irradiation

[en] The spinel MgAl₂O₄ is a ceramic with relatively high thermal conductivity and results on good behaviour under irradiation by neutrons had been published since twenty years. This material is therefore among the inert matrix studied for nuclear uses for the future: targets for the transmutation of the actinide nuclear wastes, and plutonium nuclear fuels without uranium. Unfortunately, unexpected important swellings (up to more than 20%) had been measured after some of our recent irradiations with neutrons and fission products in nuclear fission reactors. On the other hand, these results on swelling are not systematically reproducible. This study has been done to determine the influent parameters on the behaviour of the ceramics under irradiation and particularly on the swelling. The polished surface of different disks of sintered polycrystalline spinel have been irradiated at room temperature and 500 deg C, at different fluencies between 10¹¹ and 5.10¹⁶ ions/cm², with different heavy ions (from S to Pb) of energy up to more than 1 GeV. Disks of ZnAl₂O₄ spinel have been also irradiated in the same conditions for more accurate characterisation of the irradiated zone by grazing XRD. The influence of electronic stopping power and fluence on the deviation of the lattice parameter of the oxides will be analysed: the lattice parameter variation presents a maximum for dE/dx near 7 keV/nm. The conditions for amorphization will be discussed, and the damages produced by nuclear stopping power or electronic stopping power will be compared. Characterisation of the defects has been done by optical spectroscopy before and after irradiation, and the results will be reported. The influence of the spinel tested (purity, grain size, density and internal stress) on the behaviour under irradiation will be analyzed. Outline of mechanism of ceramic damage under irradiation will be presented. (authors)

[en] When a material is subjected to a flux of high-energy particles, its constituent atoms can be knocked from their equilibrium positions with a wide range of energies, depending on the exact nature of the collision. The spectrum of damage energy, derived from the exact knowledge of the recoil spectra for each nuclear reaction occurring in the solid, constitutes a vital data set required for understanding how materials evolve under irradiation. The project will be aimed at using the latest, most modern nuclear data to produce, evaluate and assess the damage energy spectra for a range of nuclear-relevant materials. The knowledge of such a damage energy is relevant to compare the impact of different facilities on the structural behaviour and relevant properties of materials

[en] Grazing X-ray diffraction was used to study in details the behaviour of two spinels, ZnAl₂O₄ and MgAl₂O₄ irradiated by swift ions. Such an irradiation allows to have an important irradiated depth and then accurate diffraction diagrams. Rietveld refinement done on these diagrams clearly show an order-disorder transition due to a melting of cations under irradiation in these two spinels. More especially, these results clearly exhibit that no new phase is created under irradiation in MgAl₂O₄. Raman spectroscopy, sensitive to the crystallographic space group, seems to confirm this analysis

[en] Boron carbide, B₁₂C₃, is an absorbing material used to control the reactivity of nuclear reactors by taking advantage of nuclear reactions (e.g. ¹⁰B(n,α)⁷Li), where neutrons are absorbed. During such reactions, radiation damages originating both from these nuclear reactions and from elastic collisions between neutrons and atoms lead to a partial destruction of this material, which gives the main limitation of its lifetime in nuclear reactors. In order to understand the evolution of B₁₂C₃ in nuclear plants, the effect of neutron irradiation in B₁₂C₃ has been investigated by Raman and nuclear magnetic resonance (NMR) spectroscopies. Comparisons of B₁₂C₃ samples irradiated by 1 MeV electrons, 180 keV helium ions and neutrons are used to study the microstructure evolution of this material by Raman scattering. The analysis of Raman spectra of different B₁₂C₃ samples irradiated by neutrons clearly shows that during the cascade displacements, the 485 and 527 cm^-1 modes disappear. These characteristic features of Raman spectra of the neutron irradiated samples are interpreted by a microscopic model. This model assumes that the CBC linear chain is destroyed whereas icosahedra are self-healed. ¹⁰B atoms destroyed during the neutron irradiation are replaced in icosahedra by other boron and carbon atoms coming from the linear CBC chain. The ¹¹B NMR analysis performed on unirradiated and irradiated B₄C samples shows the vanishing of a strong quadrupolar interaction associated to the CBC chain during the high neutron irradiation. The ¹¹B NMR spectroscopy confirms the previous Raman spectroscopy and the proposed microscopic model of B₁₂C₃ evolution under neutron irradiation