摘要:

Most people seem to agree that the 5f state in the uranium chalcogenides is a relatively broad (about 1 eV wide) band1and in Cm compounds the 5f state is localized. We follow the width and hybridization of the 5f states from the uranium chalcogenides to AmTe. The simple crystal structure and the availability of large single crystals permitted new and unusual measurements. The electrical transport properties (measured between dc and optical frequencies), the magnetic susceptibilities and magnetization (between 1K and 1000 K, and between 10 Oe and 100 kOe), and the specific heat and its &ggr; value are correlated to derive the electronic structure and relative arrangement of p, d and f states. In addition to electronic properties the elastic and phononic properties are measured and used to support the electronic structure. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1292188

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We are using the techniques of neutron and x-ray powder diffraction to learn more about the driving forces for structural transformations in Pu metal. This research is currently being conducted in three areas: (1) understanding the low melting point of Pu, (2) measuring the intergranular stresses that arise in solid-solid phase transitions of Pu, and (3) determining whether the idiosyncratic crystal structures of Pu are stabilized by Pu atoms in different valence states at different crystallographic sites. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1292189

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Substitution of plutonium (Pu) by so-called deltagen elements (Ga, Al, Am, Ce&ellip;) allows us to stabilize the high-temperature expanded fcc &dgr;-phase of Pu at room temperature or down to 4 K, depending on the concentration of the deltagen.1The nature of this stabilization is still a question of fundamental interest. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1292190

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The magnetic scattering of x-rays is a weak process, difficult to observe even with present day synchrotrons if heavy elements, with their associated high absorption cross sections, are used. A decade ago it was discovered that by tuning the photon energy to an absorption edge there is often a large enhancement of the magnetic signal. Some of the largest signals are, in fact, found at the M edges (which lie around 4 keV) of the actinides. This is because these resonant energies signify transitions from core3dto empty orbits in the5fshells, and it is electrons in the5fshells of the actinides that give rise to their magnetism. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1292191

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

It has been evident for some time that the unusual structural behavior found in plutonium is related to the localization mechanism for the5felectrons in going from alpha to delta plutonium. The atomic volume expands by sharply defined steps at the alpha-to-beta, beta-to-gamma, and gamma-to-delta transition temperatures. Here we explain this behavior on the basis of a multistep5flocalization process involving spatially nonuniform localization. That is, we suggest that a disordered array of two types of plutonium on crystallographically equivalent fcc sites breaks the translational symmetry and provides an entropy generating mechanism that drives the transition to the delta structure. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1292192

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Despite extensive work over several decades, the electronic structure of Pu in its various allotropes is not yet understood in detail. It is generally accepted that f-bands in &agr;-Pu are strongly hybridized with 6d bands, and moreover that there may exist direct f-f overlap, while in &dgr;-Pu there is a much greater tendency toward localization of the 5f electrons. Since photoemission spectroscopy (PES) is the most direct experimental tool for probing the electronic structure of materials, it is utilized to observe the assumed differences described above. We report PES results on &agr;- and &dgr;-Pu using a laser plasma light source (LPLS) as well as HeI and HeII radiation. Surprisingly, we find only minimal differences in the electronic structures of &agr;- and &dgr;-Pu (except near the Fermi energy) despite large differences in structural and mechanical properties. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1292193

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The measurement of elastic moduli can provide crucial input to fundamental descriptions of the electronic structure and thermodynamics of Pu because elastic moduli play a leading role in determining how thermal energy is distributed among internal vibrations, which, for the most part, control the entropy at ambient temperatures and above. In addition, elastic moduli are important parameters for engineering processes related to the fabrication and function of Pu components and are often the most sensitive of physical parameters to changes in material properties with age, composition or temperature. We describe here the rationale, techniques, and results for recent studies of the elastic moduli of Pu. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1292194

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The worldwide civilian use of nuclear energy generates yearly about 11,000 tons of spent-fuel from 433 nuclear power plants (NPP) in operation for the moment with an installed capacity of approximately 350 GWe (36 NPP are being under construction). This contributes to the world electricity production about 17&percent;. The hitherto discharged spent-fuel is estimated to be around 220,000 tons, which contain about 1,400 tons of plutonium and a considerable amount of minor actinides and fission products. The total quantity of long-lived radioactive elements mostly actinides, increases steadily. The foreseeable solution for their isolation from the biosphere is a geological disposal with safe confinement. The long-term safety assessment of such containment entails well-founded knowledge on the aquatic chemistry of actinides, most of all, their thermodynamic properties in the geochemical environment. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1292195

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

In the present work, we have performed a series of laboratory batch sorption experiments of plutonium (IV) on zeolite (clinoptilolite) colloids to understand the role of colloids in the transport of plutonium under groundwater conditions similar to those found at the NTS. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1292196

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

To understand the environmental behavior of metals we must consider a tremendous range of phenomena, from simple individual reactions, such as ligand complexation and solubility equilibria, to quite complicated and collective processes, such as metal-mineral-microbial interactions. Because of pressing contamination problems at DOE sites and the paucity of relevant actinide chemistry knowledge, research is needed in this entire range of science. The determination and evaluation of key thermodynamic data for actinide species and the development of geochemical, hydrological, and environmental transport models are progressing. In contrast, we know almost nothing about how actinides interact with microorganisms. Ubiquitous microorganisms can absorb, reduce, oxidize, solubilize, or precipitate actinides, thereby affecting their speciation, solubility, bioavailability, and migration. These effects are due to both direct and indirect interactions, such as sorption to the cell wall and reaction with microbial byproducts, respectively. Our goal is to fully characterize specific microbial-actinide interactions, both to develop this area of fundamental research and to determine how the interactions may be exploited to affect environmental actinide mobility/immobility and remediation efforts. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1292197

出版商:AIP    

年代:1900

数据来源: AIP