2 billion year old natural analogs for nuclear waste disposal: the natural nuclear fission reactors in Gabon (Africa)

Two billion years ago, the increase of oxygen in atmosphere and the high ²³⁵U/²³⁸U uranium ratio (>3%) made possible the occurrence of natural nuclear reactors on Earth. These reactors are considered to be a good natural analogue for nuclear waste disposal. Their preservation during such a long period of time is mainly due to the geological stability of the site, the occurrence of clays surrounding the reactors and acting as an impermeable shield, and the occurrence of organic matter that maintained the environment in reducing conditions, favourable for the stability of uraninite. Hydrogeochemical studies and modelling have shown the complexity of the geochemical system at Oklo and Bangombé (Gabon) and the lack of precise data about uranium and fission products retention and migration mechanisms in geological environments. To cite this article: F. Gauthier-Lafaye, C. R. Physique 3 (2002) 839–849.     

Photoinduced multipolar tensorial patterning in polymer films by coherent control of molecular orientation

Based on an early proposition by R.J. Glauber in 1967, the possibility to break centrosymmetry in molecular media by interference between one- and two-photon absorption pathways has been implemented in polymers throughout the last decade. This effect has been more recently advantageously generalized to optically induce adjustable multipolar molecular ordering in polymer thin films for nonlinear optics. A major benefit of this approach lies in the control of the final molecular orientational distribution by pure optical parameters such as phase or polarization of write beams. In this article, we extend a tensorial multipolar engineering experiment to encompass tensorial monitoring of photo-induced molecular orientational orders up to the 4th order. Coherent control of optical write beams, combined with real-time tensorial probing of optical properties in the material, provide access to a complete characterization of each excitation pathway contributing to the process. To cite this article: S. Brasselet et al., C. R. Physique 3 (2002) 479–492.     

Shedding light on the nanoworld: diffusion-limited nanostructures from laser-focused atom deposition

We study the role of surface diffusion in the fabrication of nanostructures by laser-focused (“cold”) atom lithography, using kinetic Monte Carlo simulations of a growth model that accounts for spontaneous organisation of 3D islands. Contrary to intuition, we find that the lateral size of the nanostructures is barely affected by surface diffusion of deposited adatoms, even when the adatom diffusion length exceeds the standing-wave field wavelength. To cite this article: F. Nita, A. Pimpinelli, C. R. Physique 5 (2004).     

Global variational calculations of high-resolution rovibrational spectra: isotopic effects,intensity anomalies and experimental confirmations for H2S,HDS, D2S molecules

Variational calculations of high-resolution infrared molecular spectra for isotopically substituted triatomic molecules from potential and dipole moment functions are discussed. A study of intensity anomalies and of their isotopical behavior especially for symmetry-breaking substitutions represents a particularly interesting subject. Extreme manifestations of intensity anomalies present in spectra of the hydrogen sulfide molecule are considered. A first qualitative experimental confirmation of reported theoretical results for deuterium containing species is discussed. To cite this article: Vl.G. Tyuterev et al., C. R. Physique 5 (2004).     

Fuels and targets for transmutation

The major technological aspects of fuels and targets for the transmutation of minor actinides are discussed. The changes in the fuel properties, the effects on the fabrication processes and the irradiation behaviour caused by recycling of minor actinides (compared to conventional uranium-based fuel) are outlined. The most promising developments are identified. To cite this article: R.J.M. Konings, D. Haas, C. R. Physique 3 (2002) 1013–1022.     

Mechanical properties of carbon nanotubes: theoretical predictions and experimental measurements

Mechanical properties of carbon nanotubes are discussed based on recent advances in both modeling and experiment. To cite this article: R.S. Ruoff et al., C. R. Physique 4 (2003).     

Molecules in nuclei

The possible existence of analogues of atomic molecules within nuclei is considered in the context of the neutron-rich beryllium and carbon isotopes, where the underlying α cluster structure is believed to produce a multi-centred potential in which valence neutrons move. The generation of molecular wave-functions is examined and the link with the deformed harmonic oscillator and the Nilsson single-particle level scheme traced. Experimental evidence for the existence of molecular exotic cluster structures is reviewed particularly the nature of spectroscopic information provided by break-up reaction measurements. To cite this article: M. Freer, C. R. Physique 4 (2003).     

Experimental results: an update

This article is a summary of experimental results from highest energy cosmic ray measurements, focusing on data and analyses that became available after 1999. To cite this article: R. Engel, H. Klages, C. R. Physique 5 (2004).     

Radionuclides retention: from macroscopic to microscopic

In order to determine the radionuclides' sorption constants on solid natural minerals, both thermodynamic and structural investigations, using spectroscopic techniques, are presented. The natural clays, that could be used as engineering barriers in the nuclear waste geological repository, are rather complex minerals. Therefore, in order to understand how these natural materials retain the radionuclides, it is necessary first to perform these studies on simple substrates such as single crystal, oxides and silicates, and then extrapolate the obtained results on the natural minerals. We examine in this paper the sorption processes of the hexavalent uranium on zircon (ZrSiO₄) and the trivalent curium on a natural clay (bentonite). The corresponding sorption curves are simulated using the results obtained with the following spectroscopic techniques: laser induced spectrofluorimetry, X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (EXAFS), diffuse reflectance infrared Fourier transform (DRIFT). To cite this article: E. Simoni, C. R. Physique 3 (2002) 987–997.     

CMB polarization as complementary information to anisotropies

The origin of CMB polarization is reviewed. Special emphasis is placed on the cosmological information encoded in it: the nature of primordial fluctuations, the connection with the inflation paradigm. Insights into more recent epochs are also discussed: early reionization and high redshift matter distribution from CMB lensing. To cite this article: J. Kaplan et al., C. R. Physique 4 (2003).     

Can the CMB reveal the topology of the universe?

This article summarizes recent progress in the development of tools to study the topology of the universe with the cosmic microwave background. The different signatures of the topology and observational constraints are described. The ability of future experiments to reveal the topological structure of our universe is then discussed. To cite this article: J.P. Uzan, A. Riazuelo, C. R. Physique 4 (2003).     

Comment on “A new model of charge transfer during ice–ice collisions”: [C. R. Physique 3 (2002) 1293–1303]

A model which proposes modifications of a theory of collisional charging of ice is criticized. To cite this article: J.G. Dash, J.S. Wettlaufer, C. R. Physique 4 (2003).     

Helium and point defect accumulation: (ii) kinetic modelling

The main outstanding issues regarding modeling He diffusion and defect accumulation in α-iron are reviewed. During recent years, first principles calculations have provided a better understanding of defect stability and migration properties in pure α-iron, and accurate values of energetics of He migration and He-vacancy interactions. Such information has been used by several authors to study damage evolution under different irradiation conditions using both kinetic Monte Carlo and rate theory models. In this article a review of the main results is provided, in particular for He desorption. The influence of impurities such as carbon is discussed as well as the main challenges ahead for modeling. To cite this article: M.J. Caturla et al., C. R. Physique 9 (2008).     

Searching for extra dimensions at colliders

The phenomenology as well as the main experimental aspects of large extra space dimensions at colliders are briefly presented. To cite this article: M. Besançon, C. R. Physique 4 (2003).     

InP-based wavelength tunable vertical cavity surface emitting laser structures

We report on the design, fabrication and characteristics of both hybrid and monolithic micro-electro-mechanically wavelength tunable 1.55 μm InP-based Vertical-Cavity Surface-Emitting Laser (VCSEL) structures. Photo-pumped tunable VCSELs are successfully realized using both configurations, and a design for electrically pumped tunable VCSEL is presented. To cite this article: I. Sagnes et al., C. R. Physique 4 (2003).     

The international Boltzmann project – the contribution of the PTB

To support new determinations of the Boltzmann constant, which have been requested by the International Committee for Weights and Measures (CIPM) and which are necessary for preparative steps towards new definitions of the kilogram, the ampere, the kelvin and the mole, an iMERAPlus joint research project is coordinating the European activities in this field in Spain (CEM), Denmark (DFM), France (LNE-INM/CNAM, University Paris North), Italy (INRiM, Universities of Naples and Milan), United Kingdom (NPL), Germany (PTB) and in the European Institute for Reference Materials and Measurements (IRMM). In this major European research project, the Boltzmann constant will be determined with various methods. The aims and the progress to date of the PTB contribution are reviewed in this article. To cite this article: B. Fellmuth et al., C. R. Physique 10 (2009).     

Diffusion kurtosis imaging for the assessment of renal fibrosis of chronic kidney disease: A preliminary study

Purpose: To investigate the potential of diffusion kurtosis imaging (DKI) for the assessment of renal fibrosis in chronic kidney disease (CKD), using histopathology as the reference standard.Methods: Eighty-nine CKD patients and twenty healthy volunteers were recruited in this study. DKI was performed in all participants and all CKD patients received renal biopsy. The values of mean diffusivity (MD) and mean kurtosis (MK) in the renal cortex and medulla were compared between CKD patients and healthy volunteers. The Spearman correlation coefficient was calculated to assess the relationship between MD, MK values and the estimated glomerular filtration rate (eGFR), serum creatinine (SCr), 24 h urinary protein (24 h-UPRO), histopathological fibrosis score.Results: The medullary MD values were significantly lower than cortex, while the cortical MK values were significantly lower than medulla for all participants. Renal parenchymal MD values were significantly lower in the CKD patients than healthy controls, whereas MK values were significantly higher in the CKD patients than healthy controls. In the CKD patients, the significantly negative correlation was observed between the renal parenchymal MD values and the 24 h-UPRO, SCr, histopathological fibrosis score, as well as between the renal parenchymal MK values and the eGFR, while the significantly positive correlation was found between the renal parenchymal MD values and the eGFR, as well as between the renal parenchymal MK values and the 24 h-UPRO, SCr, histopathological fibrosis score.Conclusion: DKI shows great potential in the noninvasive assessment of renal fibrosis in CKD.     

High-brightness diode lasers

The basic concepts and some modelling aspects of high-brightness semiconductor lasers are reviewed. The technology of lasers with a tapered gain-region is described. They provide the highest brightness of a semiconductor source with continuous wave emission in the visible and near infrared spectral range. Experimental results are presented for tapered lasers emitting at 735 nm and 808 nm. Output powers of 3 W were achieved in nearly diffraction limited beams. To cite this article: H. Wenzel et al., C. R. Physique 4 (2003).     

Ion irradiation of TNOs: from the fluxes measured in space to the laboratory experiments

Cosmic ion irradiation is believed to be one of the processes driving the evolution of the surface materials on TNOs. We review the laboratory simulations of radiation effects induced in likely TNO materials. In particular the production of new molecular species, the formation of refractory organics, and the spectral changes induced in icy targets and in natural bitumens are described. In order to establish if the effects seen in the laboratory are in fact responsible for the surface properties of the TNOs, the present knowledge of the ion fluxes is reviewed. For objects at selected solar distances, dosage time is given versus depth into the material. As suggested by recent experiments, the contribution of the electronic energy loss and that due to knock-on collisions are given separately. The relevance of ion-irradiation for the physico-chemical properties of TNOs is demonstrated, and the need for future investigations is outlined. To cite this article: G. Strazzulla et al., C. R. Physique 4 (2003).     

International views on nuclear safety

Safety has always been an important objective in nuclear technology. Starting with a set of sound physical principles and prudent design approaches, safety concepts have gradually been refined and cover now a wide range of provisions related to design, quality and operation. Research, the evaluation of operating experiences and probabilistic risk assessments constitute an essential basis and international co-operation plays a significant role in that context. Concerning future developments a major objective for new reactor concepts, such as the EPR, is to practically exclude a severe core damage accident with large scale consequences outside the plant. To cite this article: A. Birkhofer, C. R. Physique 3 (2002) 1059–1065.