X ray diffraction investigation of Pu-Ce and Pu-Ce-Ga alloys stabilized in the delta-phase

International audienceIn the actinides series (progressive filling of the 5f-sub shell), Pu interlinks the light actinides withdelocalized 5f electrons, and the heavy actinides with localized Sf electrons. At this boundary, 8-Pu is a hightemperature allotrope with an intermediate Sf behaviour. It reaches stability at room temperature by alloying withdeltagen solutes like At, Ga, Am, Ce. X-Ray Diffraction showed that the Sf electrons of 5Pu tend to delocalize in thePu-Al and Pu-Ga alloys (Ga and Al atoms are smaller than 8-Pu atoms) whereas they tend to localize in the Pu-Amalloys (Am atoms are bigger than 8-Pu atoms). Ce atoms, also bigger than 8-Pu atoms, are expected to induce asimilar behaviour as Am atoms. However, in the Pu-Ce alloys, Ce atoms exhibit an aiiotropic transformation(y-Ce->a-Ce) caused by the lattice strains: a derealization of the 4f electrons of Ce involves a reduction of itsatomic volume and disturbs the investigation of the Sf electrons behaviour. In this work, some Pu-Ce and Pu-Ga-Cealloys were studied and showed a cooperative deltagen effect of Ga and Ce. This result, together with previousstudies in literature, indicates that the mechanism of the 8 phase stabilization by Ce and Am are not equivalent. Itseems mat the localization of the Sf electrons of Pu by Ce alloying is uncertain. Photoemision measurements areplanned in order to confirm this hypothesis

ENDOMMAGEMENT SOUS CHOC DE L'ALLIAGE D'ALUMINIUM AU4G

Des essais de choc de plaques ont permis d'étudier l'endommagement d'un alliage d'aluminium AU4G. Une procédure expérimentale simple, fondée uniquement sur la connaissance de la vitesse d'impact et sur l'observation microscopique des cibles récupérées a été utilisée pour quantifier l'endommagement en fonction de la pression de choc. Cet endommagement est, par ailleurs, simulé à l'aide d'une approche théorique dérivée du modèle NAG.Damage in a 2024 aluminium alloy is studied by means of plate impact experiments. The experimental procedure, based on the projectile velocity measurement and on microscopic observations of recovered targets, has been used to quantify the damage. The experimental results are compared with theoretical prediction calculated with a code derived from NAG model

Fracture initiation of metals at high loading rates

SIGLEAvailable from CEN Saclay, Service de Documentation, 91191 Gif-sur-Yvette Cedex (France) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Influence of strain-rate on the flow stress and ductility of copper and tantalum

SIGLEAvailable from CEN Saclay, Service de Documentation, 91191 Gif-sur-Yvette Cedex (France) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Etude du cisaillement adiabatique en compression dynamique

Available from CEN Saclay, Service de Documentation, 91191 Gif-sur-Yvette Cedex (France) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc

Magnetic Properties of Radiation Damage in Pu and Pu Alloys

Among the many exceptional properties of Pu is its apparent lack of either local moments or cooperative magnetism. Lashley et al., have recently noted that little experimental evidence for the existence of local moments or collective magnetism has been found in over 50 years. Nevertheless the search for local moments in Pu and Pu-alloys continues, why? Plutonium's physical properties: resistance, magnetic susceptibility, and heat capacity, all support a system with an enhanced electron density of states. Pu sits on the edge of both magnetism and superconductivity and possesses one of the highest elemental Pauli susceptibilities, consistent with a highly correlated electron system. The low-density {delta}-Pu has eluded full first principles description and is both a challenge and an area of active investigation for theorists. The complex changes associated with the transition between the light and heavy actinides happen within the phase diagram of Pu, thus making Pu an intriguing and challenging solid-state system for continuing experimental and theoretical investigation. Recently, Griveau et al., observed the variations in the resistance and superconducting properties of Am metal as a function of pressure to 27GPa and T>0.4K. They postulate that the interesting features in the superconducting critical temperature, T{sub c}, vs. pressure, indicate a Mott-like, f-electron localization-delocalization transition as pressure drives Am towards a Pu and then a U-like structure. Hence, we posit that it would be reasonable to expect that dilating the Pu lattice will bring one to a similar transition. Experimental evidence supporting this point of view is given here

Self-Irradiation Effects in Plutonium Alloys Stabilized in the delta-Phase.

Abstract not availableJRC.E-Institute for Transuranium Elements (Karlsruhe

Character of 5f5f states in the Pu-Am system from magnetic susceptibility, electrical resistivity, and photoelectron spectroscopy measurements

International audienceAlloying Pu with Am stabilizes the fcc structure of $\delta$−Pu for all temperatures and expands the lattice. $\delta$-Pu is assumed close to the borderline of $5f$ localization. It is a nonmagnetic strongly correlated system, which should be sensitive to doping or lattice expansion. However, magnetic susceptibility, electrical resistivity, and photoelectron spectroscopy studies performed for the Pu-rich part (from 5 to 43 % Am) of the Pu-Am phase diagram indicate that the character of the $5f$ states does not vary with the Am doping. These findings are discussed within the present debate about the electronic structure of plutonium