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Equation of State of Uranium and Plutonium  [PDF]
Dalton Ellery Gir?o Barroso
Physics , 2015,
Abstract: The objective of this work is to define the parameters of the three-term equation of state for uranium and plutonium, appropriate for conditions in which these materials are subjected to strong shock compressions, as in cylindrical and spherical implosions. The three-term equation of state takes into account the three components of the pressure that resist to compression in the solid: the elastic or "cold" pressure (coulombian repulsion between atoms), the thermal pressure due to vibratory motion of atoms in the lattice of the solid and the thermal pressure of electrons thermally excited. The equation of state defined here permits also to take into account the variation of the specific heat with the transition of the solid to the liquid or gaseous state due to continued growth of temperature in strong shock compressions. In the definition of uranium equation of state, experimental data on the uranium compression, available in the open scientific literature, are used. In the plutonium case, this element was considered initially in the alpha-phase or stabilized in the delta-phase. In the last case, an abrupt and instantaneous transition to the alpha-phase was considered when the delta-phase plutonium is submitted to strong compressions.
Janusz Adamski
Bulletin of the Institute of Heat Engineering , 1988,
Abstract: In this paper the production of plutonium isotopes in the nuclear reactor core has been investigated. The effect of the resonances and fluex magnitude and fuel enrichment on the concentration growth of plutonium has been shown.
Absence of magnetic moments in plutonium  [PDF]
J. C. Lashley,A. C. Lawson,R. J. McQueeney,G. H. Lander
Physics , 2004, DOI: 10.1103/PhysRevB.72.054416
Abstract: Many theories published in the last decade propose that either ordered or disordered local moments are present in elemental plutonium at low temperatures. We present new experimental data and review previous experimental results. None of the experiments provide any evidence for ordered or disordered magnetic moments (either static or dynamic) in plutonium at low temperatures, in either the alpha- or delta-phases. The experiments presented and discussed are magnetic susceptibility,electrical resistivity, NMR, specific heat, and both elastic and inelastic neutronscattering. Many recent calculations correctly predict experimentally observed atomic volumes, including that of delta-Pu. These calculations achieve observed densities by the localization of electrons, which then give rise to magnetic moments. However, localized magnetic moments have never been observed experimentally in Pu. A theory is needed that is in agreement with all the experimental observations. Two theories are discussed that might provide understanding of the ensemble of unusual properties of Pu, including the absence of experimental evidence for localized magnetic moments; an issue that has persisted for over 50 years.
Plutonium and Quantum Criticlity  [PDF]
G. Chapline,M. Fluss,S. McCall
Physics , 2007,
Abstract: The unusual properties of elemental plutonium have long been a puzzle. It has been suggested that these properties may be related to quantum criticality [G. Chapline, J. L. Smith LA Sci 26 (2000) 1]. In this talk we will describe some experimental observations on rare earth and actinide materials which suggest that there are pairing correlations in all f-electron metals, and that the anomalous properties of the elemental actinides in the vicinity of Np/Pu/Am,even at elevated temperatures, is associated with a critical point in the variation of the density of paired electrons with atomic number.
Energetics and Electronic Structure of Plutonium  [PDF]
Nicola Lanatà,Yong-Xin Yao,Cai-Zhuang Wang,Kai-Ming Ho,Gabriel Kotliar
Physics , 2014,
Abstract: Plutonium is the most exotic and mysterious element in the periodic table. It has 6 metallic phases and peculiar physical properties not yet understood. One of the most intriguing properties of Pu is that relatively small changes of temperature can induce transitions between different structures, that are accompanied by very large changes of equilibrium volumes. This fact has stimulated extensive theoretical and experimental studies. In spite of this, a convincing explanation of the metallurgic properties of Pu based on fundamental principles is still lacking, and none of the previous theories has been able to describe simultaneously the energetics and the $f$ electronic structure of all of the phases of Pu on the same footing. Here we provide a bird's eye view of Pu by studying the zero-temperature pressure-volume phase diagram and the $f$ electronic structure of all of its crystalline phases from first principles. In particular, we clarify the way in which the $f$-electron correlations determine its unusual energetics. Our theoretical energetics and ground-state $f$ electronic structure are both in good quantitative agreement with the experiments.
Theory of Antineutrino Monitoring of Burning MOX Plutonium Fuels  [PDF]
A. C. Hayes,H. R. Trellue,Michael Martin Nieto,W. B. WIlson
Physics , 2011, DOI: 10.1103/PhysRevC.85.024617
Abstract: This letter presents the physics and feasibility of reactor antineutrino monitoring to verify the burnup of plutonium loaded in the reactor as a Mixed Oxide (MOX) fuel. It examines the magnitude and temporal variation in the antineutrino signals expected for different MOX fuels, for the purposes of nuclear accountability and safeguards. The antineutrino signals from reactor-grade and weapons-grade MOX are shown to be distinct from those from burning low enriched uranium. Thus, antineutrino monitoring could be used to verify the destruction of plutonium in reactors, though verifying the grade of the plutonium being burned is found to be more challenging.
The Valence-Fluctuating Ground State of Plutonium  [PDF]
M. Janoschek,Pinaki Das,B. Chakrabarti,D. L. Abernathy,M. D. Lumsden,J. M. Lawrence,J. D. Thompson,G. H. Lander,J. N. Mitchell,S. Richmond,M. Ramos,F. Trouw,J. -X. Zhu,K. Haule,G. Kotliar,E. D. Bauer
Physics , 2015, DOI: 10.1126/sciadv.1500188
Abstract: A central issue in material science is to obtain understanding of the electronic correlations that control complex materials. Such electronic correlations frequently arise due to the competition of localized and itinerant electronic degrees of freedom. While the respective limits of well-localized or entirely itinerant ground states are well-understood, the intermediate regime that controls the functional properties of complex materials continues to challenge theoretical understanding. We have used neutron spectroscopy to investigate plutonium, which is a prototypical material at the brink between bonding and non-bonding configurations. Our study reveals that the ground state of plutonium is governed by valence fluctuations, that is, a quantum-mechanical superposition of localized and itinerant electronic configurations as recently predicted by dynamical mean field theory. Our results not only resolve the long-standing controversy between experiment and theory on plutonium's magnetism, but also suggest an improved understanding of the effects of such electronic dichotomy in complex materials.
Avoided Valence Transition in a Plutonium Superconductor  [PDF]
B. J. Ramshaw,A. Shekhter,R. D. McDonald,J. B. Betts,J. N. Mitchell,P. H. Tobash,C. H. Mielke,E. D. Bauer,A. Migliori
Physics , 2014, DOI: 10.1073/pnas.1421174112
Abstract: Some of the most remarkable phenomena---and greatest theoretical challenges---in condensed matter physics arise when $d$ or $f$ electrons are neither fully localized around their host nuclei, nor fully itinerant. This localized/itinerant "duality" underlies the correlated electronic states of the high-$T_c$ cuprate superconductors and the heavy-fermion intermetallics, and is nowhere more apparent than in the $5f$ valence electrons of plutonium. Here we report the full set of symmetry-resolved elastic moduli of $PuCoGa_5$---the highest $T_c$ superconductor of the heavy fermions ($T_c$=18.5 K)---and find that the bulk modulus softens anomalously over a wide range in temperature above $T_c$. Because the bulk modulus is known to couple strongly to the valence state, we propose that plutonium valence fluctuations drive this elastic softening. This elastic softening is observed to disappear when the superconducting gap opens at $T_c$, suggesting that plutonium valence fluctuations have a strong footprint on the Fermi surface, and that $PuCoGa_5$ avoids a valence-transition by entering the superconducting state. These measurements provide direct evidence of a valence instability in a plutonium compound, and suggest that the unusually high-$T_c$ in this system is driven by valence fluctuations.
Electronic structure and energetics of praseodymium and $α$-plutonium under pressure  [PDF]
Nicola Lanatà,Yongxin Yao,Cai-Zhuang Wang,Kai-Ming Ho,Gabriel Kotliar
Physics , 2014,
Abstract: We develop a new implementation of the Gutzwiller approximation (GA) and interface it with the local density approximation (LDA). This formulation enables us to study complex $4f$ and $5f$ systems. We perform calculations of praseodymium and $\alpha$-plutonium under pressure, which compare very well with the experiments. Our study of praseodymium indicates that both structure change and $f$-delocalization are important to obtain the correct phase diagram and, in particular, the pressure-induced volume-collapse transition. Our calculations of $\alpha$-plutonium indicate that, even though the $f$ electrons are delocalized in this phase, the electron-correlations affect substantially its electronic structure and thermodynamical properties.
Modeling Superionic Behavior of Plutonium Dioxide  [PDF]
S. D. Günay,B. Akgen?,?. Ta?seven
Physics , 2015,
Abstract: The Bredig transition to the superionic phase indicated with the lambda-peak in Cp was highly expected for PuO2 as other actinide dioxides. However, least-square fit and local smoothing techniques applied to the experimental enthalpy data of plutonium dioxide in 80's could not detect a lambda-peak in specific heat that might be due to too scattered and insufficient experimental data. Therefore, this issue has not been yet put beyond the doubts. In the current article, a superionic model of PuO2 is developed with partially ionic model of a rigid ion potential. Thermophysical properties were calculated in constant pressure-temperature ensemble using molecular dynamics simulation. The Bredig transition with vicinity of a lambda-peak in specific heat was a successfully observed for the model system at about 2100K. Moreover, the experimental enthalpy change was well reproduced before and after the estimated transition temperature.
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