Bordeaux Gradignan Center of Nuclear Studies

Gradignan, France

Bordeaux Gradignan Center of Nuclear Studies

Gradignan, France
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Avez B.,Bordeaux Gradignan Center of Nuclear Studies | Avez B.,French National Center for Scientific Research | Bender M.,Bordeaux Gradignan Center of Nuclear Studies | Bender M.,French National Center for Scientific Research
Physical Review C - Nuclear Physics | Year: 2012

We derive an expression that allows for the unambiguous evaluation of the overlap between two arbitrary quasiparticle vacua, including its sign. Our expression is based on the Pfaffian of a skew-symmetric matrix, extending the overlap formula recently proposed by Robledo to the most general case of quasiparticle vacua, including the one of the overlap between two different blocked n-quasiparticle states for either even or odd systems. The powerfulness of the method is illustrated for a few typical matrix elements that appear in realistic angular-momentum-restored generator coordinate method calculations when breaking time-reversal invariance and using the full model space of occupied single-particle states. © 2012 American Physical Society.

Yao J.M.,Free University of Colombia | Yao J.M.,Southwest University | Bender M.,Bordeaux Gradignan Center of Nuclear Studies | Heenen P.-H.,Free University of Colombia
Physical Review C - Nuclear Physics | Year: 2015

Background: Electron scattering provides a powerful tool to determine charge distributions and transition densities of nuclei. This tool will soon be available for short-lived neutron-rich nuclei. Purpose: Beyond-mean-field methods have been successfully applied to the study of excitation spectra of nuclei in the whole nuclear chart. These methods permit determination of energies and transition probabilities starting from an effective in-medium nucleon-nucleon interaction but without other phenomenological ingredients. Such a method has recently been extended to calculate the charge density of nuclei deformed at the mean-field level of approximation [J. M. Yao, Phys. Rev. C 86, 014310 (2012)PRVCAN0556-281310.1103/PhysRevC.86.014310]. The aim of this work is to further extend the method to the determination of transition densities between low-lying excited states. Method: The starting point of our method is a set of Hartree-Fock-Bogoliubov wave functions generated with a constraint on the axial quadrupole moment and using a Skyrme energy density functional. Correlations beyond the mean field are introduced by projecting mean-field wave functions on angular momentum and particle number and by mixing the symmetry-restored wave functions. Results: We give in this paper detailed formulas derived for the calculation of densities and form factors. These formulas are rather easy to obtain when both initial and final states are 0+ states but are far from being trivial when one of the states has a finite J value. Illustrative applications to Mg24 and to the even-mass Ni58-68 have permitted an analysis of the main features of our method, in particular the effect of deformation on densities and form factors. An illustrative calculation of both elastic and inelastic scattering form factors is presented. Conclusions: We present a very general framework to calculate densities of and transition densities between low-lying states that can be applied to any nucleus. Achieving better agreement with the experimental data will require improving the energy density functionals that are currently used and also introducing quasiparticle excitations in the mean-field wave functions. © 2015 American Physical Society.

Dermer C.D.,U.S. Navy | Yan D.,CAS Institute of High Energy Physics | Yan D.,Yunnan University | Zhang L.,Yunnan University | And 2 more authors.
Astrophysical Journal | Year: 2015

Fermi-LAT analyses show that the γ-ray photon spectral indices of a large sample of blazars correlate with the peak synchrotron frequency according to the relation . The same function, with different constants d and k, also describes the relationship between and peak Compton frequency . This behavior is derived analytically using an equipartition blazar model with a log-parabola description of the electron energy distribution (EED). In the Thomson regime, for external Compton (EC) processes and for synchrotron self-Compton (SSC) processes, where b is the log-parabola width parameter of the EED. The BL Lac object Mrk 501 is fit with a synchrotron/SSC model given by the log-parabola EED, and is best fit away from equipartition. Corrections are made to the spectral-index diagrams for a low-energy power-law EED and departures from equipartition, as constrained by absolute jet power. Analytic expressions are compared with numerical values derived from self-Compton and EC scattered γ-ray spectra from Ly broad-line region and IR target photons. The versus behavior in the model depends strongly on b, with progressively and predictably weaker dependences on γ-ray detection range, variability time, and isotropic γ-ray luminosity. Implications for blazar unification and blazars as ultra-high energy cosmic-ray sources are discussed. Arguments by Ghisellini et al. that the jet power exceeds the accretion luminosity depend on the doubtful assumption that we are viewing at the Doppler angle. © 2015. The American Astronomical Society. All rights reserved..

Dermer C.D.,U.S. Navy | Cerruti M.,Harvard - Smithsonian Center for Astrophysics | Cerruti M.,University of Paris Descartes | Lott B.,Bordeaux Gradignan Center of Nuclear Studies | And 2 more authors.
Astrophysical Journal | Year: 2014

Blazar spectral models generally have numerous unconstrained parameters, leading to ambiguous values for physical properties like Doppler factor δD or fluid magnetic field B′. To help remedy this problem, a few modifications of the standard leptonic blazar jet scenario are considered. First, a log-parabola function for the electron distribution is used. Second, analytic expressions relating energy loss and kinematics to blazar luminosity and variability, written in terms of equipartition parameters, imply δD, B′, and the peak electron Lorentz factor . The external radiation field in a blazar is approximated by Lyα radiation from the broad-line region (BLR) and 0.1 eV infrared radiation from a dusty torus. When used to model 3C 279 spectral energy distributions from 2008 and 2009 reported by Hayashida et al., we derive δD20-30, B′few G, and total (IR + BLR) external radiation field energy densities u10-2-10-3 erg cm -3, implying an origin of the γ-ray emission site in 3C 279 at the outer edges of the BLR. This is consistent with the γ-ray emission site being located at a distance R ≲ Γ2 ct var0.1(Γ/30)2(t var/104 s) pc from the black hole powering 3C 279's jets, where t var is the variability timescale of the radiation in the source frame, and at farther distances for narrow-jet and magnetic-reconnection models. Excess ≳ 5 GeV γ-ray emission observed with Fermi LAT from 3C 279 challenges the model, opening the possibility of a second leptonic component or a hadronic origin of the emission. For low hadronic content, absolute jet powers of 10% of the Eddington luminosity are calculated. © 2014. The American Astronomical Society. All rights reserved.

Carjan N.,Horia Hulubei National Institute of Physics and Nuclear Engineering | Carjan N.,Bordeaux Gradignan Center of Nuclear Studies | Rizea M.,Horia Hulubei National Institute of Physics and Nuclear Engineering
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2015

The main properties of the neutrons released during the neck rupture are calculated for U236 in the frame of a dynamical scission model: the angular distribution with respect to the fission axis (on spheres of radii R=30 and 40 fm and at time T=4×10-21s), the distribution of the average neutron energies (for durations of the neck rupture δT=1 and 2×10-22s) and the total neutron multiplicity (for two values of the minimum neck-radius rmin=1.6 and 1.9fm). They are compared with measurements of prompt fission neutrons during U235(nth,f). The experimental trends are qualitatively reproduced, i.e., the focusing of the neutrons along the fission axis, the preference of emission from the light fragment, the range, slope and average value of the neutron energy-spectrum and the average total neutron multiplicity. © 2015.

Dermer C.,U.S. Navy | Lott B.,Bordeaux Gradignan Center of Nuclear Studies
Journal of Physics: Conference Series | Year: 2012

Some questions raised by Fermi-LAT data about blazars are summarized, along with attempts at solutions within the context of leptonic models. These include both spectral and statistical questions, including the origin of the GeV breaks in low-synchrotron peaked blazars, the location of the gamma-ray emission sites, the correlations in the spectral energy distributions with luminosity, and the difficulty of synchrotron/SSC models to fit the spectra of some TeV blazars. © Published under licence by IOP Publishing Ltd.

Ortega R.,Bordeaux Gradignan Center of Nuclear Studies
Particle and fibre toxicology | Year: 2014

The mechanisms of toxicity of metal oxide particles towards lung cells are far from being understood. In particular, the relative contribution of intracellular particulate versus solubilized fractions is rarely considered as it is very challenging to assess, especially for low-solubility particles such as cobalt oxide (Co3O4). This study was possible owing to two highly sensitive, independent, analytical techniques, based on single-cell analysis, using ion beam microanalysis, and on bulk analysis of cell lysates, using mass spectrometry. Our study shows that cobalt oxide particles, of very low solubility in the culture medium, are readily incorporated by BEAS-2B human lung cells through endocytosis via the clathrin-dependent pathway. They are partially solubilized at low pH within lysosomes, leading to cobalt ions release. Solubilized cobalt was detected within the cytoplasm and the nucleus. As expected from these low-solubility particles, the intracellular solubilized cobalt content is small compared with the intracellular particulate cobalt content, in the parts-per-thousand range or below. However, we were able to demonstrate that this minute fraction of intracellular solubilized cobalt is responsible for the overall toxicity. Cobalt oxide particles are readily internalized by pulmonary cells via the endo-lysosomal pathway and can lead, through a Trojan-horse mechanism, to intracellular release of toxic metal ions over long periods of time, involving specific toxicity.

Ortega R.,Bordeaux Gradignan Center of Nuclear Studies | Carmona A.,Bordeaux Gradignan Center of Nuclear Studies | Llorens I.,Synchrotron Soleil | Solari P.L.,Synchrotron Soleil
Journal of Analytical Atomic Spectrometry | Year: 2012

X-ray absorption spectroscopy (XAS) is an element specific spectroscopy sensitive to the local chemical and structural order of the absorber element. XAS is nowadays increasingly used for the speciation analysis of chemical elements owing to the development of new synchrotron radiation facilities worldwide. XAS can be divided into X-ray absorption near edge structure (XANES), which provides information primarily about the geometry and oxidation state, and extended X-ray absorption fine structure (EXAFS), which provides information about metal site ligation. The main advantages of the XAS method are its subatomic (angstrom) resolution, the ability to analyze almost any type of samples including amorphous (non-crystalline) materials, the possibility to analyze such materials in situ requiring minor or no sample preparation. The main limitations of XAS are its sensitivity in the mM (or μg g-1) range, the difficulty to deconvolute the bulk data when the sample is composed of a mixture of structures of the absorber element, and the limited chemical selectivity of ligands to within one row of the periodic table. This tutorial will discuss the strengths and limitations of XAS and compare them to those of alternative or complementary methods such as X-ray diffraction and X-ray photoelectron spectroscopy. The tutorial will also present and discuss the specific needs in terms of sample preparation and preservation all along the process of storage and analysis, and discuss the importance of the use of cryogenic methods when XAS is applied to biological samples. Applications in life sciences are reviewed, not exhaustively, with a special emphasis on some characteristic examples. The article ends with some perspectives on future trends of XAS: micro- and nano-XAS, time-resolved XAS, and high energy resolution XAS. © 2012 The Royal Society of Chemistry.

Barberet P.,Bordeaux Gradignan Center of Nuclear Studies | Seznec H.,Bordeaux Gradignan Center of Nuclear Studies
Radiation Protection Dosimetry | Year: 2015

Charged-particle microbeams (CPMs) allow the targeting of sub-cellular compartments with a counted number of energetic ions. While initially developed in the late 1990s to overcome the statistical fluctuation on the number of traversals per cell inevitably associated with broad beam irradiations, CPMs have generated a growing interest and are now used in a wide range of radiation biology studies. Besides the study of the low-dose cellular response that has prevailed in the applications of these facilities for many years, several new topics have appeared recently. By combining their ability to generate highly clustered damages in a micrometric volume with immunostaining or live-cell GFP labelling, a huge potential for monitoring radiation-induced DNA damage and repair has been introduced. This type of studies has pushed end-stations towards advanced fluorescence microscopy techniques, and several microbeam lines are currently equipped with the state-of-the-art time-lapse fluorescence imaging microscopes. In addition, CPMs are nowadays also used to irradiate multicellular models in a highly controlled way. This review presents the latest developments and applications of charged-particle microbeams to radiation biology. © The Author 2015.

Lott B.,Bordeaux Gradignan Center of Nuclear Studies
International Journal of Modern Physics D | Year: 2010

The first three months of sky-survey operation with the Large Area Telescope (LAT) on board the Fermi satellite revealed 132 bright sources at |b| > 10° with test statistic greater than 100 (corresponding to about 10σ). Two methods, based on the CGRaBS, CRATES and BZCat catalogs, indicated high-confidence associations of 106 of these sources with known AGNs. This sample is referred to as the LAT Bright AGN Sample (LBAS). It contains two radio galaxies, namely Centaurus A and NGC 1275, and 104 blazars consisting of 58 flat spectrum radio quasars (FSRQs), 42 BL Lac objects, and four blazars with unknown classification. Remarkably, the LBAS includes 10 high-energy-peaked BL Lacs. Only 33 of the sources, plus two at |b| < 10°, were previously detected with EGRET, probably due to variability. The analysis of the gamma-ray properties of the LBAS sources reveals that the average GeV spectra of BL Lac objects are significantly harder than the spectra of FSRQs. Other spectral and variability blazar properties are discussed. Some prominent Fermi-detected radiogalaxies are presented. © 2010 World Scientific Publishing Company.

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