Safety procedures for the electron spectroscopy of actinides at the ALS

This is an addendum to the ALS Experimental Safety Form Renewal for the continuation of actinide microspot experiments on beamlines 7.0. There are several modifications to the previously approved. procedures. There is an increase in the amount of allowable material of the low activity isotopes {sup 238}U, {sup 237}Np, {sup 242}Pu, and {sup 248}Cm. There is also the addition of {sup 99}Tc and the activity isotopes {sup 232}Th and {sup 243}Am to the list of permissible sample materials. All of the materials are alpha-emitters with negligible gamma fields with the exception of {sup 99}Tc which is a beta-emitter. There is a series of new experiments that requires the use of a crystal cleaver in the preparation chamber of the ultraESCA end station. The beamline 7.0 ultraESCA endstation has been suitably modified to permit the safe cleave of YUPd alloy rectangular ingots. AR of the sample materials are solids. The exact nature and composition of the samples are delineated in the sample preparation section that follows. A corresponding Radiological Work Authorization (RWA) must be issued for this work at ALS since the material amounts exceed those in the Low Activity Source (LAS) guidelines in Table I and those in the Values for Exemption of Sealed Source Inventory in Table II. The preliminary date for the next run of these sample materials has been tentatively scheduled in early February 1996 and this will be with the uranium cleave alloys, not the transuranic materials

EXAFS spectroscopic studies of uranium(VI) oxide precipitates

We have investigated the structures of U(VI) oxides precipitated from room temperature aqueous solutions at low ionic strength as a function of pH. Using the uranium L{sub III} - edge extended x-ray absorption fine structure (EXAFS) as a probe of the local structure around the uranium, a trend is observed whereby the axial oxygen bond lengths from the uranyl groups increase from 1.80 {Angstrom} at pH=7 to 1.86 {Angstrom} at pH=11. A concomitant decrease in the equatorial oxygen and nearest-neighbor uranium bond lengths also occurs with increasing pH. Expansion of the linear O=U=O group is seen directly at the L{sub III} absorption edge where multiple scattering resonances systematically shift in energy. EXAFS curve-fitting analysis on these precipitates and a sample of synthetic schoepite indicate that the structure of the species formed at pH=7 is similar to the structure of schoepite. At pH=11, the precipitate structure is similar to that of a uranate

Soft X-ray synchrotron radiation investigations of actinidematerials systems utilizing X-ray emission spectroscopy and resonantinelastic X-ray scattering

Synchrotron radiation (SR) methods have been utilized with increasing frequency over the past several years to study topics in actinide science, ranging from those of a fundamental nature to those that address a specifically-targeted technical need. In particular, the emergence of microspectroscopic and fluorescence-based techniques have permitted investigations of actinide materials at sources of soft x-ray SR. Spectroscopic techniques with fluorescence-based detection are useful for actinide investigations since they are sensitive to small amounts of material and the information sampling depth may be varied. These characteristics also serve to simplify both sample preparation and safety considerations. Examples of investigations using these fluorescence techniques will be described along with their results, as well as the prospects for future investigations utilizing these methodologies

Studies of Actinides Reduction on Iron Surfaces by Means ofResonant Inelastic X-ray Scattering

The interaction of actinides with corroded iron surfaces was studied using resonant inelastic x-ray scattering (RIXS) spectroscopy at actinide 5d edges. RIXS profiles, corresponding to the f-f excitations are found to be very sensitive to the chemical states of actinides in different systems. Our results clearly indicate that U(VI) (as soluble uranyl ion) was reduced to U(IV) in the form of relatively insoluble uranium species, indicating that the iron presence significantly affects the mobility of actinides, creating reducing conditions. Also Np(V) and Pu (VI) in the ground water solution were getting reduced by the iron surface to Np(IV) and Pu (IV) respectively. Studying the reduction of actinides compounds will have an important process controlling the environmental behavior. Using RIXS we have shown that actinides, formed by radiolysis of water in the disposal canister, are likely to be reduced on the inset corrosion products and prevent release from the canister

Actinide Spectroscopy Workshop

Actinide materials present an extreme scientific challenge to the materials research community. The complex electronic structures of actinide materials result in many unusual and unique properties that have yet to be fully understood. The difficulties in handling, preparing, and characterizing actinide materials has frequently precluded investigations and has the limited the detailed understanding of these relevant, complex materials. However, modern experiments with actinide materials have the potential to provide key, fundamental information about many long-standing issues concerning actinide materials. This workshop focused on the scientific and technical challenges posed by actinide materials and the potential that synchrotron radiation approaches available at the ALS can contribute to improving the fundamental understanding of actinides materials. Fundamental experimental approaches and results, as well as theoretical modeling and computational simulations, were part of the workshop program

Environmental applications of XANES: Speciation of {Tc} in cement after chemical treatment and Se after bacterial uptake

XANES (X-ray Absorption Near Edge Spectroscopy) has been employed to evaluate the efficacy of a process designed to encapsulate and reduce {Tc}O{sub 4}{sup {minus}} in cement matrices, thereby immobilizing {Tc}. The oxidation state of Se following.bioremediation of Se by bacteria has also been determined by XANES. The XANES measurements were performed at the Stanford Synchrotron Radiation Laboratory (SSRL) and the National Synchrotron Light Source (NSLS) at the respective K edges of {Tc} (21.0 keV) and Se (12.7 keV). Comparison of the XANES spectra of Tc in untreated cement to Tc in slag treated cement and to the chemical shifts of reference materials, shows that the oxidation state of {Tc} is the same in both cements. Thus, the addition of a reducing agent to the cement formulation does not significantly reduce the {Tc}O{sub 4} The common soil bacterium, Bacillus subtilis, is known to incorporate Se on or within the cell wall when exposed to a SE(IV) solution. The Se XANES spectra of B. subtilis, as well as bacillus isolated from selenium rich soil, show that the organisms reduce selenite to the red allotrope of elemental Se

Research program to investigate the fundamental chemistry of technetium. 1998 annual progress report

'Technetium ({sup 99}Tc, {beta} emitter, half-life 2.1 x 10{sup 5} years, spA= 1.7 x 10{sup -2} Ci/g) is one of the radionuclides of major concern because of regulatory considerations for radioactive waste disposal. The propensity of Tc as pertechnetate, TcO{sub 4}{sup -}, to migrate in the geosphere necessitates its safe, long-term immobilization. Technetium is found in the nuclear waste storage tanks at the Hanford and at the Savannah River sites in highly alkaline environments along with multi-molar concentrations of nitrate, nitrite, and Na ions and lesser amounts of organic complexants, phosphate, sulfate chloride, fluoride, and carbonate. It has been assumed that technetium is present in the waste tanks as the pertechnetate ion but a recent study has suggested that at least in part, technetium is present in another form. There is a lack of information on Tc chemistry in oxidation states III-V with simple inorganic (OH{sup -}, CO{sub 3}{sup 2-}, PO{sub 4}{sup 3-}, SiO{sub 4}{sup 4-}) and common organic ligands (EDTA, citrate, oxalate) under alkaline conditions. This is essential information needed for pretreatment schemes, processing, and the assessment of stability of Tc in waste form materials. Further complicating the Tc waste tank chemistry is the added effect of an intense radiation field originating from {sup 137}Cs and {sup 90}Sr. The interactions of the ionizing radiation with water, nitrate, nitrite, and other minor components create highly reactive species that can strongly perturb the oxidation-reduction conditions. The stability of Tc in waste form materials is of paramount importance for long term storage concerns and the solid state chemical properties of many candidate Tc compounds are unknown. There have been few systematic studies of Tc stability in lower valent solids with the exception of TcO{sub 2}. Thus, it is not possible at present to assess the long term stability of many Tc compounds relevant to proposed waste form materials. This experimental research program addresses the characterization of the chemistry of technetium pertinent to the waste tank environment and to various waste forms. The solution and solid state chemistry of this element will be studied in aqueous solutions as a function of pH with the various salts added such as nitrate and nitrite, and as a function of radiation dose. The second part of this program is a search for stable, lower valent Tc materials which may prove useful for waste storage. This report summarizes the results after nine months of a three year project.

Unfilled orbitals of c-60 and c-70 from carbon k-shell x-ray absorption fine-structure

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