The chalk is the most extensive French aquifer, and numerous tracer tests are executed here each year to delimit the protection zones of water supply wells. In the karstic chalk of Normandy, only 49 % of the tracer tests emerge at one of the monitoring points and subsequently pass into the water distribution network where they generally undergo chlorination. The majority of the tracers remains adsorbed in the subsurface or emerges at other points, notably untapped springs, in which case the tracers reach surface streams where they can be degraded by photolysis. Here, we study the degradation in the laboratory of three of the main fluorescent tracers, submitted to a chlorine flow or a strong luminosity. The tests were carried with concentrations greatly higher than the maximum ever recorded during tracer tests in chalk. In spite of an important degradation, the tests carried out on the by-products of degradation show an absence of acute toxicity and a moderate ecotoxicity, except for naphthionate (to relativize due to the high tested concentrations).

The synthesis of niobium nitride by reactive diffusion in a furnace at 1395–1475°C and under nitrogen pressure in the range 2–25MPa was investigated. In experiments, we used compacted Nb powder with a mean particle size of 43μm. Phase transformations in the product as studied by electron probe microanalysis (EPMA) were found to proceed in the following order: Nb→α-Nb(N)→β-Nb2N1±x→γ-Nb4N3±x→δ-NbN1±x. The size of niobium particles which could react with nitrogen to yield cubic niobium nitride was estimated (SEM analysis) from the dependence of the thickness Δ of the δ-NbN1±x outer layer formed on the surface of Nb particles on the dwell time tdw at 1460–1473°C. It was shown that Δ grew nearly proportional to tdw. At tdw=30min and P(N2)=2MPa, Δ was found to attain a value of about 15.5μm. Prolonged heating (tdw≈60min) was found to result in decomposition of the single-phase cubic niobium nitride into a two-phase (multiphase) product. This was confirmed by XRD data and magnetic measurements which showed the occurrence of two different critical temperatures Tc in the same sample. The maximum critical temperature Tc was found to attain a value of 15.6K.

Our laboratory is involved in the French EUV (Extreme Ultra-Violet) program PREUVE to develop Mo/Si mirrors for blanks free of defects by using an ion beam sputtering deposition technique. This paper illustrates a reduction strategy used to lead to an EUV mirror with a defect density as low as possible. One of the methods adopted is the analysis of the process step by step, therefore, the defect number added by each process step has been quantified. It appears that the most critical step is substrate cleanness. Today, our best performance for a final mirror is 1.2 def/cm2 with a defect size >200 nm. This value has been measured on our home-made counting device COMNET. Our counting device has been validated by comparison with a commercial tool. Two improvements have been implemented on COMNET to increase its routine performance which allows to detect particles of 200 nm. The first one is the sample illumination with a laser in oblique incidence (60°) which increases the signal-to-noise ratio. The noise is the roughness of the sample. The second one is the implementation of a cooled CCD camera with a variable exposure time. Thanks to these improvements, the detection of particles with a diameter size of 155 nm has been demonstrated. On the basis of the experimental results and calculations, the detection of 100 nm particles on silicon and EUV blanks can be reasonably predicted.