The equilibrium H-and O-isotope fractionations can be approximated by the following equations which are based on experimental, empirical and/or theoretical data:Hydrogen: 1000 In ~kaolinite-water ~" -2.2 x 106 X T -2 -7.7 Oxygen: 1000 In ~kaolinite-water = 2.76 x 106 • _ 6.75 1000 In (~smectite-water = 2.55 x 106x T -2 -4.05 1000 In ~illite-water = 2.39 X 106 • T -2 -3. 76 The equilibrium H-isotope fractionation factors vs. 106 • T -2 for kaolinite and probably smectite and illite are monotonic curves between 350-0~ More complex curves, with a minimum fractionation near 200~ are probably influenced by surface effects and/or disequilibrium fractionations among the different hydrogen sites. The H-isotope fractionations between smectite-water increase by 70% from Fe-poor montmorillonite to nontronite at low temperatures. The pore-interlayer water in smectite H-isotope fractionation at low temperatures is ~20__+ 10%. The presence of organic matter can modify both the ~SD value of the clay analysis and its 'water' content. Clays --kaolinite, illite, smectite and probably halloysite --tend to retain their D/H and 180/160 ratios unless subjected to more extreme diagenetic or metamorphic conditions or special local processes. Kinetic information is still only qualitative: for comparable grain sizes, hydrogen exchanges more rapidly than oxygen in the absence of recrystallization. Low-temperature diffusion coefficients cannot be calculated with sufficient precision from the higher temperature exchange data. The H-and O-isotope studies of clays can provide useful information about their conditions of formation.Studies of the stable isotope ratios D/H (or 2H/1H) and lSO/160 of clay minerals effectively started with Savin's thesis (1967; see Saviu & Epstein, 1970a,b). They established a number of general isotopic systematics of clay minerals from continental and oceanic environments at surface temperatures. Subsequent studies on natural samples and laboratory experiments (see review by Savin & Lee, 1988 and references therein) have developed the stable isotope geochemistry of clay minerals to a wide range of applications such as: geothermometry; provenance of clays: detrital vs. authigenic; diagenetic processes; origin and evolution of upper crustal fluids; hypogene vs. supergene origin; hydrothermal systems; mineral-water interaction; and palaeoclimates.All of these applications depend directly or indirectly on knowledge of: (1) the H-and O-isotope fractionation factors in clay-water systems (unless specified to the contrary, water is used to refer to the aque0us-rich fluid phase that is associated with the clay; it may be more or less saline); and (2) the temperature and time when isotopic exchange with and/or in the clay ceased. Either equilibrium or kinetic isotope fractionation with another phase is responsible for variations in the isotopic compositions of clays. Equilibrium isotopic fractionation factors are a function of temperature. However, variations in the chemical composition of the mineral may be o...

HADES is a versatile magnetic spectrometer aimed at studying dielectron production in pion, proton and heavy-ion induced collisions. Its main features include a ring imaging gas Cherenkov detector for electron-hadron discrimination, a tracking system consisting of a set of 6 superconducting coils producing a toroidal field and drift chambers and a multiplicity and electron trigger array for additional electron-hadron discrimination and event characterization. A two-stage trigger system enhances events containing electrons. The physics program is focused on the investigation of hadron properties in nuclei and in the hot and dense hadronic matter. The detector system is characterized by an 85 % azimuthal coverage over a polar angle interval from 18• to 85• , a single electron efficiency of 50 % and a vector meson mass resolution of 2.5 %. Identification of pions, kaons and protons is achieved combining time-of-flight and energy loss measurements over a large momentum range. This paper describes the main features and the performance of the detector system.

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