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This paper presents a scheme of an x‐ray spectrometer with exchangeable secondary targets and investigation of its characteristics. A high‐voltage power source with a voltage up to 75 kV and x‐ray tubes with power up to 2.5 kW were used in the spectrometer to generate the primary x‐ray radiation. The exchangeable secondary targets made it possible to get monochromatic radiation with a rather high degree of the spectral contrast. The use of tubes with different anodes materials (chromium, tungsten and rhodium) and different secondary targets provides efficient performance for the analysis of a range of concentrations of elements with atomic numbers 13 < Z < 92. In this case, it was possible to optimize the sample analysis for definite groups of elements, reaching detection limits (DL) of 10−6 g/g in aqueous solutions. According to the sensitivity (DL), this device can act as a spectrometer with total external reflection of the primary beam (TXRF spectrometer). However, its design is simpler, it has better optical efficiency, its adjustment is simple and convenient and it has a high operating efficiency. Besides, the design of the device makes it possible to perform simultaneously, if necessary, x‐ray fluorescence and x‐ray absorption analyses of a sample. Examples of the application of the device for the determination of heavy‐metal content in the aqueous solutions and measurement of thickness of films are presented in this paper. Copyright © 2007 John Wiley & Sons, Ltd.

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Most of the exoplanets with known masses at Earth-like distances to Sun-like stars are heavier than Jupiter, which raises the question of whether such planets are accompanied by detectable, possibly habitable moons. Here we simulate the accretion disks around super-Jovian planets and find that giant moons with masses similar to Mars can form. Our results suggest that the Galilean moons formed during the final stages of accretion onto Jupiter, when the circumjovian disk was sufficiently cool. In contrast to other studies, with our assumptions, we show that Jupiter was still feeding from the circumsolar disk and that its principal moons cannot have formed after the complete photoevaporation of the circumsolar nebula. To counteract the steady loss of moons into the planet due to type I migration, we propose that the water ice line around Jupiter and super-Jovian exoplanets acted as a migration trap for moons. Heat transitions, however, cross the disk during the gap opening within ≈10 4 years, which makes them inefficient as moon traps and indicates a fundamental difference between planet and moon formation. We find that icy moons larger than the smallest known exoplanet can form at about 15-30 Jupiter radii around super-Jovian planets. Their size implies detectability by the Kepler and PLATO space telescopes as well as by the European Extremely Large Telescope. Observations of such giant exomoons would be a novel gateway to understanding planet formation, as moons carry information about the accretion history of their planets.