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Symposium : M

Basic research on ionic-covalent materials for nuclear applications

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 Electronic excitations with lasers and swift heavy ions : Akihiro Iwase
09:00Nonequilibrium electron dynamics and energy dissipation during and after high-energy irradiation of dielectric solids
Authors : Baerbel Rethfeld (1), Nils Brouwer (1), Anika Raemer (1), Orkhan Osmani (2)
Affiliations : (1) Department of Physics and Optimas Research Center, TU Kaiserslautern, Germany; (2) Fakultaet für Physik, Universitaet Duisburg-Essen, Duisburg, Germany;
Resume : When dielectrics are irradiated with an ultrashort laser pulse or a swift heavy ion, the density of electrons in the conduction band is considerably increasing. This density is a crucial parameter for the subsequent behaviour of the material: After ion irradiation it influences energy dissipation to the lattice as well as the energy transport to the outer track. For the case of laser irradiation on a timescale of about hundred femtoseconds, the density increase due to irradiation also determines the further absorption of the pulse energy. Also the distribution function of the excited electrons may influence the energy absorption and dissipation. We study microscopic processes in laser-irradiated solids on ultrashort timescales. Out calculations give insights also to the case of irradiation with a swift heavy ion. Various theoretical approaches are applied to trace the non-equilibrium distribution function of the highly excited electronic system, as well as the energy transfer to the lattice and the transport of heat to the depth of the irradiated material. We check whether and to what extend the concept of temperature is applicable shortly after excitation and study in particular the dependence of the electron--phonon coupling parameter on excitation strength for different materials.
9 1
09:40Damage formation and sputtering with energetic heavy ions: Synergy effects of electronic and nuclear energy losses
Authors : M. Toulemonde1, W. Assmann2, C. Trautmann3,4, Y. Zhang5,6, M. Backman7 and W.J. Weber5,6
Affiliations : 1 CIMAP-GANIL, Caen France; 2 LMU, München, Germany, 3 GSI, Darmstadt, Germany, 4 Technische Universität Darmstadt, Darmstadt, Germany; 5 University of Tennessee, Knoxville, USA; 6 Oak Ridge National Laboratory, Oak Ridge, USA.
Resume : Experimental investigations with heavy projectiles in the energy range where nuclear and electronic energy losses are in competition show clear synergy effects. This applies for sputtering processes of Ti as well as for track formation in SiO2. The sputtering yields for metallic Ti recorded with the catcher technique under UHV conditions [1] are much larger than values expected from the TRIM-cascade code [2] and can only be described quantitatively using combined contributions from the inelastic thermal spike (electronic stopping) and the elastic collisions spike (nuclear stopping) [3]. Track formation in crystalline as well as in amorphous SiO2 quartz irradiated with energetic Au ions has revealed also synergy effects. Analyzing SiO2 quartz exposed to different fluences by channeling Rutherford Backscattering spectrometry shows a damage evolution that can be fitted by an Avrami function (1-exp(-t)n, where  is the cross section, t the fluence. The exponent n is 3.5 when the irradiation was performed in the pure nuclear energy loss regime and is unity for the pure electronic energy loss regime [4]. Irradiated vitreous silica was analyzed by infra-red absorption spectroscopy providing quantitative information on the damage cross section. The corresponding track radius is deduced by applying a Poisson law. For Au ions of energy between 0.5 and 15 MeV, the track radius varies from 4.9 to 2.6 nm, respectively [5]. These values are surprising compared vitreous SiO2 irradiated with Au ions of much higher energies with track radii from 2.4 nm at 23 MeV increasing to 5.4 nm at 168 MeV. Plotting the different radii over the entire energy range (0.5 to 168 MeV) yields a hook-shaped dependence on the beam energy. To describe this evolution of the track size, we suggest a unified approach which considers synergetic contributions from both nuclear and electronic energy losses and combines effects due to the inelastic thermal spike and the elastic collision spike. This interpretation is supported by molecular dynamics calculations [6]. [1] H. D. Mieskes, W. Assmann, F. Grüner, H. Kucal, Z. G. Wang and M. Toulemonde, Phys. Rev. B 67 (2003) 155414 [2] J. P. Biersack and L. G. Haggmark Nucl. Instr. Meth 174 (1980) 257 [3] P. Sigmund and C. Claussen, J. Appl. Phys. 52 (1981) 990 [4] M. Toulemonde, S.M.M. Ramos, H. Bernas, C. Clerc, B. Canut, J. Chaumont and C. Trautmann Nucl. Instr. Meth. B 178 (2001) 331 [5] M. Toulemonde, W. J. Weber, G. Li, V. Shutthanandan, P. Kluth, T. Yang, Y. Wang and Y. Zhang Phys. Rev. B 83 (2011) 054106 [6] M. Backman, F. Djurabekova, O. H. Pakarinen, K. Nordlund, Y. Zhang, M. Toulemonde and W. J. Weber (2012) J. Phys. D: Appl. Phys. 45 (2012) 505305
9 2
10:00Coffee break
10:30TEM study of damage recovery in SiC by swift Xe ion irradiation
Authors : V.A. Skuratov, J. O'Connell , A.S.Sohatsky, J. Neethling
Affiliations : Joint Institute for Nuclear Research, Dubna, Russia; Centre for HRTEM, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa
Resume : Dense electronic excitations in wake of swift heavy ions are able to induce an epitaxial recrystallization of the damage created by low energy ion irradiation in silicon carbide [1-3]. This effect was studied mainly using RBS/C technique and very limited TEM data on this subject are available [2]. In this report we discuss the results of TEM examination of SiC samples predamaged by 20 keV (1e16 cm-2) He and 220 keV (1e14, 1e15 cm-2) Ti ions and then irradiated with 167 MeV Xe ions (2e12 - 1e14 cm-2). It was shown that no, or negligible defect recovery is observed in fully amorphous layers. High energy Xe ion induced recrystallization is detected in partially amorphous areas and is most significant in the subsurface layer.
9 3
10:50A MULTI-SCALE APPROACH TO ION-IRRADIATION EFFECTS ON MECHANICAL PROPERTIES OF SIC COMPOSITES.
Authors : J. Huguet-Garcia1*, A. Jankowiak1, S. Miro2, Y. Serruys2, C. Grygiel3, I. Monnet3, and J-M. Costantini1
Affiliations : 1.CEA, DEN, SRMA, F-91191 Gif-sur-Yvette, France; 2.CEA, DEN, SRMP, F-91191 Gif-sur-Yvette, France.; 3 CIMAP, CEA, CNRS, Université de Caen, F14070 Caen cedex 5, France.
Resume : Third generation SiC fibers have significantly improved the thermo-mechanical properties of SiCf/SiC ceramic matrix composites, which are considered as advanced materials for nuclear system applications. In order to determine if the SiCf/SiC can fully comply with the requirements of nuclear applications, a multi-scale approach related to these materials is currently ongoing. In this work, irradiation effects are studied in these materials by both in and ex-situ experiments at JANNUS (Saclay) and GANIL (Caen) facilities. We firstly investigated the mechanical stress induced by recrystallization in SiC single crystal, fibers and composites simultaneously irradiated with 4MeV Au ions from RT to 300°C. Indeed, for fully amorphized samples (threshold determined by Raman spectroscopy) annealed at T> 850°C, surface cracking and irradiated layer exfoliation were found. Moreover, in the composites, it has been shown that cracks mainly occur in the matrix along the residual stress lines revealed by Raman mapping in the virgin composite. In a second time, regarding specifically the fibers, we performed in-situ tensile tests (300 MPa) at high temperatures (1000ºC) and under ion-irradiation (9MeV C3+, 12MeV C4+ and 92MeV Xe23+) on single SiC fiber. Irradiation-enhanced creep was evidenced since the strain rate was increased up to 2.5 depending on the ion flux. Also, a strong dependence between the residual strain and the damage profile homogeneity across the fiber was also found.
9 4
11:10Microstructural changes in swift heavy ions ?irradiated graphite
Authors : M. Tomut 1,2, C. Hubert 1,3, M. Krause 1,3, S. Amirthapandian 4, C. Trautmann 1,3
Affiliations : 1GSI, Darmstadt, Germany; 2NIMP, Bucharest, Romani; 3TU Darmstadt, Germany; 4MSD, IGCAR, Kalpakkam, India
Resume : The present work assesses damage in the nuclear and electronic stopping regimes in swift heavy ion ?irradiated graphite by means of Raman spectroscopy, X-Ray diffraction (XRD) and scanning electron microscopy (SEM). High density polycrystalline graphite grades are used as materials for collimators, targets and beam dumps in high-power heavy ion accelerators. Lifetime prediction for these components requests a basic understanding of microstructural changes due to intense electronic excitation within the ions tracks and related material property degradation mechanisms. Depth evolution of the damage along the ion trajectory was monitored by XRD using a micrometer size X-ray beam. Cross-section micro- Raman spectra within the irradiated graphite layer show that the graphitic structure evolves toward glassy carbon in the case of electronic stopping regime and towards nanocrystalline carbon in the elastic collisions regime. For highly oriented pyrolitic graphite (HOPG), a model material for the layered graphitic structure, the depth information was obtained by stepwise cleaving thin sample layers. In this case, Raman spectra show that damage mechanism is less efficient in the region dominated by electronic stopping than in the nuclear stopping regime.
9 5
11:30Damage creation in porous silicon irradiated by swift heavy ions
Authors : B. Canut 1, M. Massoud 1, P. Newby 1, V. Lysenko 1, L. Frechette 2, J.M. Bluet 1, I. Monnet 3
Affiliations : 1 Université de Lyon, Institut des Nanotechnologies de Lyon, CNRS, INSA de Lyon, France ; 2 Department of Mechanical Engineering, Université de Sherbrooke, Québec J1K 2R1, Canada ; 3 Centre de Recherche sur les Ions, les Matériaux et la Photonique, CEA-CNRS, Université de Caen, France
Resume : Mesoporous silicon (PS) samples were processed by anodising p+ Si wafers in (1:1) HF-ethanol solution. Different current densities were used to obtain three different porosities (40%, 60% and 80%). In all cases the morphology of the PS layer is columnar with a mean crystallite size between 10 nm (80% porosity) and 20 nm (40% porosity). These targets were irradiated at the IRRSUD beamline of the GANIL accelerator, using different projectiles (238U ions of 110 MeV, 130Xe ions of 91 MeV and 29 MeV) in order to vary the incident electronic stopping power Se. The fluences ranged between 1012 and 7 x 1013 cm-2. Raman spectroscopy and cross sectional SEM observations evidenced damage creation in the irradiated nanocrystallites, without any degradation of the PS layer morphology at the lowest irradiation fluences (< 3 x 1012 cm-2). For the highest doses, the columnar morphology transforms into a spongy-like structure. The damage cross sections, extracted from Raman results, increase with the electronic stopping power and with the sample porosity. At the highest Se (12.3 keV.nm-1) and the highest porosity (80%), the track diameter coincides with the crystallite diameter, indicating that only one projectile impact is able to induce the crystallite amorphization along the major part of the ion path. These results were interpretated in the framework of the thermal spike model, taking into account of the low thermal conductivity of the PS samples in comparison with that of bulk silicon.
9 6
12:00Lunch break
 Electronic excitations with swift heavy ions : Christina Trautmann
14:00Ferromagnetism of CeO2 induced by high energy heavy ion irradiation and its thermal stability
Authors : K. Shimizu(1), T. Kishino(1), N. Ishikawa(2), Y. Saitoh(3), T. Matsui(1), A. Iwase(1)
Affiliations : (1)Department of Materials Science, Osaka Prefecture University; (2)Nuclear Science and Engineering Directorate, Japan Atomic Energy Agency: (3)Takasaki Advanced Radiation Research Institute, Japan Atomic Energy Agency
Resume : We have so far reported that the ferromagnetism is induced in CeO2 sintered pellets by 200 MeV Xe ion irradiation[1]. The value of the saturation magnetization, Ms, depends on the ion-fluence. The value of Ms increases with increasing the ion-fluence and reaches a maximum value at about the fluence of 2e13/cm2, and then decreases. The ion beam induced ferromagnetism is accompanied by the lattice expansion. In the present experiment, to study the thermal stability of the ion beam induced ferromagnetism, we annealed the irradiated CeO2 specimens in the atmosphere at various temperatures from 200C to 1000C, and measured the magnetization and the lattice constant. The magnetization and the lattice constant start to change at 400C and nearly completely recover to the values before irradiation at 800-1000C. This phenomenon can be explained as follows; the specimen reduced by the ion-irradiation becomes re-oxidized through the high temperature annealing in the atmosphere, and oxygen vacancies which contribute to the appearance of ferromagnetism and the lattice expansion disappear. In the symposium, we will also discuss the effect of low energy (about 10 MeV) ion irradiation and the effect of the high temperature annealing in a vacuum, which is another method for CeO2 reduction, on the magnetism and lattice constant of CeO2. [1]K. Shimizu et. al., Nucl. Instr. Meth. B286(2012) 291-294.
10 1
14:20Role of electronic excitations on Xe migration in UO2
Authors : B. Marchand, N. Bérerd, Y. Pipon, N. Moncoffre, M. Toulemonde, T. Epicier, L. Raimbault, C. Garnier, C. Delafoy
Affiliations : AREVA, AREVA NP, 10 rue Juliette Récamier, 69 456 Lyon, France; Université de Lyon, CNRS/IN2P3, Université Lyon 1, Institut de Physique Nucléaire de Lyon, 4 rue Enrico Fermi, 69 622 Villeurbanne cedex, France; Université de Lyon, CNRS/IN2P3, Université Lyon 1, Institut de Physique Nucléaire de Lyon, 4 rue Enrico Fermi, 69 622 Villeurbanne cedex, France; Université de Lyon, CNRS/IN2P3, Université Lyon 1, Institut de Physique Nucléaire de Lyon, 4 rue Enrico Fermi, 69 622 Villeurbanne cedex, France; CIMAP, GANIL, CEA-CNRS-ENSICAEN, BP 5133, Bd H. Becquerel, 14070 Caen, France; Université de Lyon, INSA Lyon, MATEIS, UMR CNRS 5510, 7, avenue Jean-Capelle, 69621 Villeurbanne Cedex, France; Ecole des Mines de Paris, Centre de Géosciences, 35 rue Saint Honoré, F-77305 Fontainebleau cedex, France; Université de Lyon, CNRS/IN2P3, Université Lyon 1, Institut de Physique Nucléaire de Lyon, 4 rue Enrico Fermi, 69 622 Villeurbanne cedex, France;Université de Lyon, CNRS/IN2P3, Université Lyon 1, Institut de Physique Nucléaire de Lyon, 4 rue Enrico Fermi, 69 622 Villeurbanne cedex, France
Resume : During Pressurized Water Reactor operation, around 25% of the created Fission Products (FP) are gaseous (Xenon and Krypton). These last atoms, their precipitation (fission gas bubbles), migration and segregation are known to influence the thermo-mechanical properties of the UOX and MOX fuel. Moreover, Fission Gas Release (FGR) can lead to cladding failure at high burn-up. Therefore, it is crucial to determine the evolution of the bubble population associated with Xe (and Kr) migration under irradiation in order to fully predict the fuel performance in reactors. A new methodology has been developed at IPNL to measure the Xe migration in UO2. Indeed, whereas most of previous studies coupled measurements of gas release with Booth model to access diffusion parameters, we propose a direct measurement of the Xe profiles in UO2 thanks to SIMS analyses and a specific software called SDPA (SIMS Depth Profile Achievement). Depleted UO2 samples were first implanted with 136Xe at 800 keV corresponding to a projected range of 150 nm. They were then irradiated at RT, 600°C or 1000°C with 200 MeV Iodine ions corresponding to a high electronic stopping power of around 30 keV nm-1 at the surface. It is shown that Xe is mobile under swift heavy ion irradiation. SIMS and TEM characterizations reveal fission tracks. The interpretation of the Xe radiation enhanced diffusion in UO2 is proposed on the basis of the Thermal Spike model.
10 2
14:40Electronic interaction effects under Kr 74 MeV irradiation: X-Ray Diffraction study of UO2 and (U,Gd)O2 nuclear fuels
Authors : R. Delorme*1, Ch. Valot1, P. Martin 1, C. Sabathier 1, G. Trillon 2, V. Auret 3, C. Grygiel 4, S. Bouffard 4
Affiliations : 1: CEA, DEN, DEC, Département d’Etudes des Combustibles, F-13108 Saint Paul lez Durance, France ; 2: AREVA/NP SAS, 10 rue Juliette Recamier, 69456 Lyon cedex 06, France ; 3: EDF-DIN/SEPTEN, 12-14 avenue Dutriévoz, 69628 Villeurbanne cedex, France ; 4: CIMAP, CEA-CNRS-ENSICAEN-Université de Caen, Bd Henri Becquerel, 14070 Caen cedex 5, France.
Resume : (U,Gd)O2 has been used for many years as a burnable absorber in Pressurized Water Reactor (PWR). Recent Post-Irradiation Examinations of PWR irradiated (U,Gd)O2 sample have suggested that Gd could enhance High Burn-up Structure (HBS) formation. HBS formation occurs when irradiation induced damage level and fission gas content are high enough to produce microstructure evolution (i.e. micrometric fission gas bubble formation and grain subdivision). Knowledge of gadolinium effect on basic phenomena such as defects creation by electronic interactions is of main importance to better understand complex HBS formation mechanisms. Swift heavy ions such as Kr at 74 MeV are fully suitable to simulate the electronic interaction between fission products and the fuel which is one contribution of damage accumulation in reactor. The main objective of this work is to study by X-Ray Diffraction (XRD) the electronic excitation effects on as-fabricated UO2 and (U,Gd)O2 fuels and on Xe implanted samples. Xe implantations simulate the presence of fission gas atoms in fuels. XRD analyses have been performed to study diffraction peak shift and broadening in order to determine respectively lattice parameter and non-uniform strain evolution with heavy ion irradiation. Material composition (Gd content), temperature and fluence effects on irradiation induced damage accumulation have been studied in this work performed on IRRSUD beamline of GANIL. The main conclusion of this work is that the electronic interaction effect induces lattice parameter expansion and non-uniform strain increase into both UO2 and (U,Gd)O2 fuels. (U,Gd)O2 samples exhibit higher lattice parameter expansion but no effect on non-uniform strain rate increase with ion irradiation was evidenced. However, as-fabricated (U,Gd)O2 samples demonstrate initial non-uniform strain than UO2 samples due to the presence of Gd3+ cations in the lattice. These experimental results are of high interest in order to understand observation made on PWR irradiated samples (i.e. enhanced HBS formation in (U,Gd)O2).
10 3
14:40Swift heavy ion induced surface modification of calcite (CaCO3) visualized by various techniques
Authors : Dedera Sebastian, Glasmacher Ulrich Anton, Burchard Michael, Trautmann Christina
Affiliations : Institute of Earth Sciences, University of Heidelberg; Institute of Earth Sciences, University of Heidelberg; Institute of Earth Sciences, University of Heidelberg; GSI Darmstadt
Resume : Natural calcite crystals were irradiated with 106 197Au ions/cm2 of 11.1 MeV/u at the UNILAC, and with 108 238U ions/cm2 of 192 MeV/u at SIS18, GSI Darmstadt to create artificial surface and in depth damage. Prior to the experiment the surface of calcite crystals was covered with a hexagonal mask to create irradiated and non-irradiated areas. Different approaches have been undertaken to visualize the damage caused by swift heavy ions: One possibility are etching techniques at which Na-Ethylenediaminetetraacetic acid (EDTA) + 0.5 - 5% Acetic acid in 1:1 proportion and highly diluted HNO3 as etching so-lution turned out to be suitable and reproducible. The resulting etch pits show linear growth and have a size of about 12µm (±1) after 20s of etching (EDTA), respectively 15 µm (±2) after 4s of etching (HNO3). Etching has the advantages of visibility of the etch pits with an optical microscope and an easy control of size, shape and areal density of the etch pits. Another approach to investigate surface modifications are spectrographical and advanced imaging methods. Different techniques have been tried out (Raman, IR, AFM, and SEM) of which raman spectroscopy provides the best results. Heavily irradiated areas show new, previously unknown bands correlating with decreasing established bands.
10 4
15:00Effects of electronic excitation on the structural stability of Y2Ti2O7 pyrochlore oxides
Authors : N. Sellami, G. Sattonnay, C. Legros, C. Grygiel, I. Monnet, A. Debelle, L. Thomé
Affiliations : Université Paris Sud, LEMHE/ICMMO; Université Paris Sud, LEMHE/ICMMO; Université Paris Sud, LEMHE/ICMMO; CIMAP de Caen; CIMAP de Caen; Université Paris Sud, CSNSM; Université Paris Sud, CSNSM.
Resume : Pyrochlore-type oxides (A2B2O6X - Fd3m space group), where A and B are cation sites, are ordered superstructures of the ideal fluorite structure with twice the lattice constant. Yttrium titanate Y2Ti2O7 is an important member of the pyrochlore family because it exhibits various properties which make it suitable for potential applications in different domains. Recently, it was reported that Y2Ti2O7 nanoparticles could be formed in the oxide dispersion strengthened steels (ODS) that are potential candidates for structural components in nuclear fission and fusion power plants. These materials possess an improved creep resistance at high temperatures. However, their stability under irradiation should be investigated. Y2Ti2O7 polycrystals were elaborated by a standard solid-state process and single crystals were synthesized by a floating zone technique. They were irradiated with 93-MeV Xe ions at GANIL in Caen. X-ray diffraction (XRD) experiments were performed on both single and polycrystals, in order to investigate the structural modifications induced by high electronic excitation. Moreover, the phase transformation build-up was followed by in situ XRD experiments using the ALIX setup on the IRRSUD beam line. Raman spectroscopy was also implemented in order to strengthen the knowledge of the mechanisms of phase transformation.
10 5
15:30Coffee break
16:00Wrap up discussion
 
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