Preliminary results for RR Lyrae stars and Classical Cepheids from the Vista Magellanic Cloud (VMC) Survey

The Vista Magellanic Cloud (VMC, PI M.R. Cioni) survey is collecting $K_S$-band time series photometry of the system formed by the two Magellanic Clouds (MC) and the "bridge" that connects them. These data are used to build $K_S$-band light curves of the MC RR Lyrae stars and Classical Cepheids and determine absolute distances and the 3D geometry of the whole system using the $K$-band period luminosity ($PLK_S$), the period - luminosity - color ($PLC$) and the Wesenhiet relations applicable to these types of variables. As an example of the survey potential we present results from the VMC observations of two fields centered respectively on the South Ecliptic Pole and the 30 Doradus star forming region of the Large Magellanic Cloud. The VMC $K_S$-band light curves of the RR Lyrae stars in these two regions have very good photometric quality with typical errors for the individual data points in the range of $\sim$ 0.02 to 0.05 mag. The Cepheids have excellent light curves (typical errors of $\sim$ 0.01 mag). The average $K_S$ magnitudes derived for both types of variables were used to derive $PLK_S$ relations that are in general good agreement within the errors with the literature data, and show a smaller scatter than previous studies.Comment: 7 pages, 6 figure. Accepted for publication in Astrophysics and Space Science. Following a presentation at the conference "The Fundamental Cosmic Distance Scale: State of the Art and the Gaia Perspective", Naples, May 201

The plutonium-oxygen phase diagram

Identification of products formed by the reaction of plutonium metal with liquid water at 23{degree}C indicates that the plutonium-oxygen phase diagram is similar to the cerium-oxygen and praseodymium-oxygen diagrams. Quantitative measurements of H{sub 2} formation and analytical data suggest that a sequence of hydrolysis reactions produces oxide hydrides of trivalent plutonium, Pu{sub 2}O{sub 3}, mixed-valent oxides and PuO{sub 2}. The intermediate oxides are the n {equals} 7, 9, 10 and 12 members of the Pu{sub n}O{sub 2n{minus}2} homologous series. Properties of the residue formed by thermal decomposition of the initial hydrolysis product, plutonium monoxide monhydride (PuOH), are consistent with the formation of metastable plutonium monoxide. Crystal-chemical, thermodynamic, and kinetic factors are evaluated, but definitive assignment of the equilibrium Pu-O diagram is not possible. 22 refs., 6 figs., 1 tab

Oxidation of delta-phase plutonium alloy: Corrosion kinetics in dry and humid air at 35 {degree}C

Kinetic data for oxidation of delta-phase plutonium alloy are evaluated to provide a technical basis for assessing the merit of an existing time limitation on air exposure of components during process operations. Data describing the effects of humidity and oxygen pressure on the oxidation rate of the Pu-1.0 wt% Ga alloy at elevated temperatures are obtained from literature sources and used to predict the oxidation behavior of the alloy in air at 35 C and 0 to 100% relative humidity. A mandated six-hour limit on air exposure is inconsistent with a predicted thirty-day period required for formation of a 1-{micro}m-thick oxide layer in moisture-saturated air at 35 C. Relationships are defined for predicting kinetic behavior of the alloy at other conditions, and recommendations for addressing oxidation-related concerns in production are presented

Reactions of plutonium and uranium with water: Kinetics and potential hazards

The chemistry and kinetics of reactions between water and the metals and hydrides of plutonium and uranium are described in an effort to consolidate information for assessing potential hazards associated with handling and storage. New experimental results and data from literature sources are presented. Kinetic dependencies on pH, salt concentration, temperature and other parameters are reviewed. Corrosion reactions of the metals in near-neutral solutions produce a fine hydridic powder plus hydrogen. The corrosion rate for plutonium in sea water is a thousand-fold faster than for the metal in distilled water and more than a thousand-fold faster than for uranium in sea water. Reaction rates for immersed hydrides of plutonium and uranium are comparable and slower than the corrosion rates for the respective metals. However, uranium trihydride is reported to react violently if a quantity greater than twenty-five grams is rapidly immersed in water. The possibility of a similar autothermic reaction for large quantities of plutonium hydride cannot be excluded. In addition to producing hydrogen, corrosion reactions convert the massive metals into material forms that are readily suspended in water and that are aerosolizable and potentially pyrophoric when dry. Potential hazards associated with criticality, environmental dispersal, spontaneous ignition and explosive gas mixtures are outlined

Reaction kinetics relevant to the recycle hydride-dehydride process for plutonium recovery

Objectives of this one-year, Laboratory Directed Research and Development (LDRD) project were the expansion of fundamental knowledge of plutonium chemistry and the development of information for enhancing plutonium recovery methods and weapons safety. Results of kinetic studies demonstrate that the monoxide monohydride, PuO(H), formed during corrosion of plutonium by water in pyrophoric when dry and acts as an initiator for hydride-catalyzed reaction of the metal with air. The catalyzed corrosion rate of Pu is 10{sup 8} times faster than that in dry air and transforms plutonium into a readily aerosolized material. A potential application for the catalytic reaction is in the direct recovery of plutonium as oxide. Wet PuO(H) is non-pyrophoric and the safety hazard posed by its formation is reduced if the material is not allowed to dry

White paper on possible inclusion of mixed plutonium-uranium oxides in DOE-STD-3013-96

This report assesses stabilization issues concerning mixed plutonium-uranium oxides containing 50 mass % Pu. Possible consequences of uranium substitution on thermal stabilization, specific surface areas, moisture readsorption behavior, loss-on-ignition analysis, and criticality safety of the oxide are examined and discussed