(ory, Universi~of California, tirrh Sciences Division, lCyclorron Road, Berkeley, CA 94720. I I PREFACE This report is the second document in a series of reports documenting experimental volubility and speciation studies ofradionuclides ingroundwaters from the Yucca Mountain region. The objectives and experimental concepts were discussed in detail in the first report of this series (Milestone 30 10), titled "Measured Solubilities and Speciations of Neptunium, Plutonium, and Americium in a TypicalGroundwater from the Yucca Mountain Region." I Sections 2,3, and 4 of this report are, except for minor changes, identical totheres~ctive sections of the first repofl, Theyare, however, inchsdedheretomake this report a stand-alone document. Solution concentrations of Z~TNp in contact with precipitate obtained from supersaturation of UE-25p#l groundwater at 25°C as a function of time. pH 6.() f 0.1 (closed circles), pH 7.0* 0.1 (closed triangles), and pH 8.5 * 0.1 (closed squares). The neptunium was added initially (day 0) as NpOZ+; initial concentrations were 4.8 x 103 M (pH 6), 1.5x 10-3M (pH 7), and 1.4x 103 M (pH 8.5) . ....... 22Solution concentrations of 2~TNp in contact with precipitate obtained from supersaturation of UE-25p #1 groundwater at 60°C as a function of time. pH 6.0 + (),1 (closed circles), pH 7.0+ 0.1 (closed trimrgles), and pH 8.5 * 0.1 (closed syuares). The neptunium was added initially (day O)as NpOZ+; initial concentrations were 5.6 x lo-~M (pH 6), 1.5 x 10-~M (pH 7), and 1.5 x 10-3 M (pH 8.5). The volubility-controlling steady-state solids were identified and the speciation and/or oxidation states present in the supematant solutions were determined. The neptunium sohrbility decreased with increasing temperature and pH. Plutonium concentrations significantly decreased with increasing temperature at pH 6 and 7. The concentration at pH 8.5 hardly decreased at all with increasing temperature. At both temperatures the concentrations were highest at pH 8.5, lowest at pH 7, and in between at pH 6. For the americium/neodymium solutions, the solrrbility decreased significantly with increasing temperature and increased somewhat with increasing pH. EXECUTIVE SUMMARYWe studied the soIubiIities of neptunium, plutonium, and americium in a modified UE-25p #1groundwater from the Yucca Mountain region (Nevada) at two temperatures and three hydrogen concentrations. They are 25°and 60°C and pH 6,7, and 8.5. Tables I, II, and III summarize the results for neptunium, plutonium, and americium, respectively. The nuclides were added to UE-25p #1groundwater from oversaturation at the beginning of each experiment as l~7Np02+, z~gpud+, and Nds+ with tracer 241Am~+ added to facilitate nuclear counting. Because we maintained constant pH values of 6,7, and 8.5 during the course of the ex~riments, the final sohrtions were closer to ().1 M in total ionic strength with the primary constituents being sodium and pcrchlorate. The steady-state sotids formed in the experiments may not represent the thermody...

ABSTRACT. Mechanism of two-photon induced oxidation of single-layer graphene on Si/SiO 2 substrates is studied by atomic force microscopy (AFM) and Raman microspectroscopy and imaging. AFM imaging of areas oxidized by using a tightly focused femtosecond laser beam shows that oxidation is not homogeneous but oxidized and non-oxidized graphene segregate into separate domains over the whole irradiated area. Oxidation process starts from point-like "seeds" 2 which grow into islands finally coalescing together. The size of islands before coalescence is 30 -40 nm and the density of the islands is on the order of 10 11 cm -2 . Raman spectroscopy reveals growth of the D/G band ratio along the oxidation. Sharpness of the D-band which persists over large range of oxidation and the maximal value of the intensity ratio of the D-and G-bands (~0.8) indicates that graphene oxidation proceeds by increase of the oxidized area rather than progression of oxidized areas to fully disordered structure. A phenomenological model is developed which explains the observations. According to the model, the probability for oxidation of a site next to already oxidized site is five orders of magnitude higher than oxidation of pristine graphene. Irradiation of an extended area by raster scanning leads to a formation of an irregular nanomesh of oxide islands with a narrow size distribution. The phenomenological model yields similar results as the experiment. This study forms a basis for controlled use of two-photon oxidation for tailoring properties of graphene and patterning it with sub-micrometer resolution.

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We report experimental evidence that crystalline neptunium dioxide, NpO

The rate at which elements can be transported in groundwater systems is governed in part by the solubility of the element in the groundwater. This report documents plutonium solubility experiments, conducted over the past two years at the Lawrence Berkeley Laboratory, in a brine simulant relevant to the Waste Isolation Pilot Plant. Approximately 1 to 2.5 mL of five stock solutions containing single oxidation states of plutonium (Pu(IV)-polymer, Pu 3+ , Pu 4+ , Pu0 2 + , and PuOD were added to -75 mL of synthetic H-17 Brine in five reaction vessels. Initial plutonium concentrations ranged from 1.3 X10 4 to 5.1 Χ10" 4 Μ (moles per liter) total plutonium. Because these initial concentrations were far above the plutonium solubility limit in H-17 Brine, plutonium-containing solids precipitated. Aqueous plutonium concentrations were measured over time until steadystate was reached, requiring over 300 days in H-17 Brine. Steady-state plutonium concentrations ranged from 3.0 X 10~8 to 7.6 X 10~7 M, and the predominant plutonium oxidation state in solution was Pu(VI). The solid phase from the initially Pu(IV)polymer experiment remained polymeric-Pu(IV). The solids that formed in the initially Pu 3+ and Pu 4+ experiments were crystalline yet remain unidentified. The solids that formed in the initially Pu0 2 + and PuOi + experiments appear to be sodium plutonyl(V) carbonates.