Computation and Analysis of the Global Distribution of the Radioxenon Isotope 133Xe based on Emissions from Nuclear Power Plants and Radioisotope Production Facilities and its Relevance for the Verification of the Nuclear-Test-Ban Treaty

Monitoring of radioactive noble gases, in particular xenon isotopes, is a crucial element of the verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The capability of the noble gas network, which is currently under construction, to detect signals from a nuclear explosion critically depends on the background created by other sources. Therefore, the global distribution of these isotopes based on emissions and transport patterns needs to be understood. A significant xenon background exists in the reactor regions of North America, Europe and Asia. An emission inventory of the four relevant xenon isotopes has recently been created, which specifies source terms for each power plant. As the major emitters of xenon isotopes worldwide, a few medical radioisotope production facilities have been recently identified, in particular the facilities in Chalk River (Canada), Fleurus (Belgium), Pelindaba (South Africa) and Petten (Netherlands). Emissions from these sites are expected to exceed those of the other sources by orders of magnitude. In this study, emphasis is put on ¹³³Xe, which is the most prevalent xenon isotope. First, based on the emissions known, the resulting ¹³³Xe concentration levels at all noble gas stations of the final CTBT verification network were calculated and found to be consistent with observations. Second, it turned out that emissions from the radioisotope facilities can explain a number of observed peaks, meaning that atmospheric transport modelling is an important tool for the categorization of measurements. Third, it became evident that Nuclear Power Plant emissions are more difficult to treat in the models, since their temporal variation is high and not generally reported. Fourth, there are indications that the assumed annual emissions may be underestimated by factors of two to ten, while the general emission patterns seem to be well understood. Finally, it became evident that ¹³³Xe sources mainly influence the sensitivity of the monitoring system in the mid-latitudes, where the network coverage is particularly good.     

The origin of organic matter in the Martian meteorite ALH84001.

Stable carbon isotope measurements of the organic matter associated with the carbonate globules and the bulk matrix material in the ALH84001 Martian meteorite indicate that two distinct sources are present in the sample. The delta 13C values for the organic matter associated with the carbonate globules averaged -26% and is attributed to terrestrial contamination. In contrast, the delta 13C values for the organic matter associated with the bulk matrix material yielded a value of -15%. The only common sources of carbon on the Earth that yield similar delta 13C values, other then some diagenetically altered marine carbonates, are C4 plants. A delta 13C value of -15%, on the other hand, is consistent with a kerogen-like component, the most ubiquitous form of organic matter found in carbonaceous chondrites such as the Murchison meteorite. Examination of the carbonate globules and bulk matrix material using laser desorption mass spectrometry (LDMS) indicates the presence of a high molecular weight organic component which appears to be extraterrestrial in origin, possibly derived from the exogenous delivery, of meteoritic or cometary debris to the surface of Mars.     

Phases d'érosion—comblement de la vallée de la Papenoo et volcanisme subrécent à Tahiti,en relation avec l'évolution des iles de la Société (Pacifique Sud)

A detailed mapping and data from borings support the conclusion that there is a late lava flow inside the Papenoo valley, the main valley of Tahiti island. This last volcanic manifestation which took place 400,000 years ago came after the phase of erosion corresponding to the Illinoian glacial period. It is one of the four phases of erosion followed by filling observed in the cross section of the Papenoo valley.     

Stratospheric Photolysis Frequencies: Impact of an Improved Numerical Solution of the Radiative Transfer Equation

Numerical schemes for the calculation of photolysis rates are usually employed in simulations of stratospheric chemistry. Here, we present an improvement of the treatment of the diffuse actinic flux in a widely used stratospheric photolysis scheme (Lary and Pyle, 1991). We discuss both the consequences of this improvement and the correction of an error present in earlier applications of this scheme on the calculation of stratospheric photolysis frequencies. The strongest impact of both changes to the scheme is for small solar zenith angles. The effect of the improved treatment of the diffuse flux is most pronounced in the lower stratosphere and in the troposphere. Overall, the change in the calculated photolysis frequencies in the region of interest in the stratosphere is below about 20%, although larger deviations are found for H₂O, O₂, NO, N₂O, and HCl.     

A Database for Volatile Organic Compounds

The database for volatile organic compounds (VOC data base) was created with the aim of providing an overview of tropospheric hydrocarbon measurements. The data base contains 202 substances, for which atmospheric and useful kinetic data such as rate coefficients, photolysis frequencies, mixing ratios, emission data and ozone formation potentials are compiled from available literature. The database file can be downloaded without charge from http://www.physchem.uni-wuppertal.de/voc-database. Registered users will be informed about the appearance of updates.     

A proposed new type of arsenian pyrite: Composition, nanostructure and geological significance

This report describes a new form of arsenian pyrite, called As³⁺-pyrite, in which As substitutes for Fe [(Fe,As)S₂], in contrast to the more common form of arsenian pyrite, As¹⁻-pyrite, in which As¹⁻ substitutes for S [Fe(As,S)₂]. As³⁺-pyrite has been observed as colloformic overgrowths on As-free pyrite in a hydrothermal gold deposit at Yanacocha, Peru. XPS analyses of the As³⁺-pyrite confirm that As is present largely as As³⁺. EMPA analyses show that As³⁺-pyrite incorporates up to 3.05 at % of As and 0.53 at. %, 0.1 at. %, 0.27 at. %, 0.22 at. %, 0.08 at. % and 0.04 at. % of Pb, Au, Cu, Zn, Ni, and Co, respectively. Incorporation of As³⁺ in the pyrite could be written like: As³⁺+yAu⁺+1-y(□)⇔2Fe²⁺; where Au⁺ and vacancy (□) help to maintain the excess charge. HRTEM observations reveal a sharp boundary between As-free pyrite and the first overgrowth of As³⁺-pyrite (20-40 nm thick) and co-linear lattice fringes indicating epitaxial growth of As³⁺-pyrite on As-free pyrite. Overgrowths of As³⁺-pyrite onto As-free pyrite can be divided into three groups on the basis of crystal size, 8-20 nm, 100-300 nm and 400-900 nm, and the smaller the crystal size the higher the concentration of toxic arsenic and trace metals. The Yanacocha deposit, in which As³⁺-pyrite was found, formed under relatively oxidizing conditions in which the dominant form of dissolved As in the stability field of pyrite is As³⁺; in contrast, reducing conditions are typical of most environments that host As¹⁻-pyrite. As³⁺-pyrite will likely be found in other oxidizing hydrothermal and diagenetic environments, including high-sulfidation epithermal deposits and shallow groundwater systems, where probably kinetically controlled formation of nanoscale crystals such as observed here would be a major control on incorporation and release of As³⁺ and toxic heavy metals in oxidizing natural systems.     

Chemical and structural characterization of As immobilization by nanoparticles of mackinawite (FeSm)

The mobility and availability of arsenite, As(III), in anoxic environments is largely controlled by adsorption onto iron sulfides and/or precipitation of arsenic in solid phases. The interaction of As(III) with synthetic mackinawite (FeS_m) in pH 5 and 9 suspensions was investigated using high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM), STEM elemental mapping, high resolution TEM, and X-ray photoelectron spectroscopy (XPS). At pH 5, arsenic sulfide phases precipitate among the FeS_m particles as discrete particles that are an amorphous hydrous phase of arsenic sulfide. The oxidation state of As in the surface layers of the arsenic sulfide precipitates is ‘realgar-like’ based on XPS results showing that > 75% of the As 3d peak area is due to As with oxidation states between 0 and 2+. Discrete, arsenic sulfide precipitates are absent at pH 9, but elemental mapping in STEM-EDX mode shows that arsenic is uniformly distributed on the FeS_m, suggesting that uptake is caused by the sorption of As(III) oxyanions and/or the precipitation of highly dispersed arsenic sulfides on FeS_m. XPS also revealed that the FeS_m that equilibrated without As(III) has a more oxidized surface composition than the sample at pH 9, as indicated by the higher concentration of O ( three times greater than that at pH 9) and the larger fraction of Fe(III) species making up the total Fe (2p_3/2) peak. These findings provide a better understanding of redox processes and phase transitions upon As(III) adsorption on iron sulfide substrates.     

Fractionation,hybridisation and magma-mixing in the Kialineq centre East Greenland

The igneous rocks of the Kialineq centre on the coast of East Greenland at 67°N include a number of quartz syenite and granite plutons intruded 35my BP. These are subvolcanic bodies emplaced by cauldron subsidence and with ring-dike and bell-jar form. Associated with the major intrusions is an extensive acid-basic mixed magma complex. Two-liquid structures, chilling of basic against acid magma, pillows of basic in acid, and net-veining of basic by acid magma, are superbly displayed. The basic magma was of a transitional or alkaline type and underwent varying degrees of fractionation in a regime of repeated intrusions and diverse chambers. Heterogeneous hybrid rocks intermediate between basalt and quartz syenite are strongly developed and were formed by repeated mechanical mixing of contrasting magmas. The energy for this mixing probably came in the main from cauldron-block subsidence. The quartz syenite magma, which itself fractionated towards granite, has initial ⁸⁷Sr/⁸⁶Sr ratios the same as the basic magma and is itself believed to be a fractionation product of alkali basalt magma.