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Abstract  

An analysis has been made of the surface distribution of137Cs and90Sr in soils of the province of Cáceres (Spain), of some 20.000 km2 area, situated on the frontier with Portugal. From the distribution of depth profiles of concentrations of these radionuclides and their fit to a negative exponential, determination was made of the mean values of the respective inventories and of the corresponding137Cs/90Sr ratio. The external dose rates from the presence of these man-made isotopes in the soil are calculated and compared with that originating from the concentrations of natural radioisotopes.

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Abstract  

With the object of quantifying the radiological impact that the Almaraz Nuclear Power Station, situated beside the Tajo river in Spain, induces on its ecosystem, since 1986 we have been carrying out multiple gamma-spectrometric studies and determinations of90Sr concentrations on the receptor media: surface waters, sediments, fishes, aerosols, and soils, in the two likeliest critical transmission pathways of transmission of the radioactive contamination. The principal results are summarized in the present work, and they allow the impact to be quantified, as well as the most probable source to be assigned for each of the levels detected.

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Abstract  

This paper examines the polymerization of acrylonitrile to poly(acrylonitrile)(PAN), and its cyclization, in bulk form and using N,N-dimethylformamide (DMF) as solvent in which both monomer and polymer are soluble. Thermal analysis of the resultant products after polymerization has been performed by DSC and pyrolysis gas chromatography/mass spectrometry (Py-GC/MS). Scanning electron microscopy has been used to study the morphology of the resultant products and after thermal treatments. The DSC thermal curve of PAN-DMF sample is quite different from the PAN bulk sample, showing a single sharp exothermic peak associated with nitrile group polymerization (cyclization) of PAN at lower temperature (240°C) than that of bulk PAN sample (314°C). Cyclization of PAN was confirmed by IR spectroscopy. It was found that the amide molecules are difficult to eliminate completely in the product obtained after the polymerization reaction, even after prolonged heating at 110°C, and remain occluded. The formation of a complex by dipolar bonding is also possible and it is discussed. It is concluded that the amount of heat evolved as well as the temperature interval over which it is released are influenced by the chemical processing of PAN when using DMF as solvent of both monomer and polymer. Pyrolysis of these PAN samples revealed the release of occluded molecules of DMF, and several compounds containing nitrogen produced from the thermal degradation processes. All these results are interesting to know the chemical processing of carbon fibres and activated carbon fibres from PAN modified precursors.

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Abstract  

The radioactive concentrations of226Ra,232Th,235U and40K in surface soil of the province of Cáceres (Spain) were studied as a function of the geology and grain size. The activities of the four radionuclides in granitic and metamorphic soils have normal frequency distributions, with the mean value being significantly higher for the granitic soils than for the metamorphic soils. Sedimentary soils present asymmetric distributions, and their activities lie between the previous two types. The specific activities of the four radionuclides rises as the particle radius decreases. The equationA e=(P 1/R)+P 2 describes the dependence of the specific activityA e on radiusR, P 1 andP 2 being parameters that are related to the surface area and volume activities of the grains. The isotopes226Ra,232Th and235U accumulate with greater intensity on the surface of the grains than40K. This effect is more pronounced in granitic and sedimentary soils than in metamorphic soils.

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Abstract  

We have quantified the evolution during 1994 of the impact on the Tagus river of liquid releases of3H (51.3 TBq in the cited year), originating from the functioning of the Almaraz Nuclear Power Plant, and conditioned by the management of the cooling reservoir water. Taking into account, on the one hand, that tritiated water is hydrodynamically indistinguishable from untritiated water when both form part of the same mass of liquid, and, on the other, the practically null stratification and forced circulation of the water in the cited cooling reservoir, together with the hydrological fluxes interchanged between the said reservoir and the Tagus river (which is entirely regulated in the section under study and, because of prolonged drought, had a relatively small flow during the study period), we were able to model satisfactorily the temporal evolution of the3H activity in the cooling reservoir.

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Journal of Flow Chemistry
Authors: Druval S. De Sá, Bojan A. Marinkovic, Eric C. Romani, Tommaso Del Rosso, Rodrigo O. M. A. de Souza, Alessandro Massi, and Omar Pandoli

We present prototyping of meso- and microfluidic photocatalytic devices, functionalized through incorporation of TiO2 nanoparticles in polydimethylsiloxane (PDMS), and comparison of their efficiencies for the degradation of rhodamine B (10−5 mol/L). The prototyping of the photocatalytic devices involves simple and low-cost procedures, which includes microchannels fabrication on PDMS, deposition and impregnation of TiO2 on PDMS, and, finally, plugging on the individual parts. For the microfluidic device with 13 μL internal volume, photocatalytic TiO2–PDMS composite was sealed by another PDMS component activated by O2 plasma (PDMS–TiO2–PDMS). For the mesofluidic device, a homemade polyetheretherketone (PEEK) flow cell with 800 μL internal volume was screwed on a steel support with a glass slide and the photocatalytic composite. The photocatalytic activities of the devices were evaluated using two different pumping flow systems: a peristaltic pump and a syringe pump, both at 0.05 mL/min under the action of 365 nm ultraviolet (UV) light. The characterization of TiO2–PDMS composite was performed by confocal Raman microscopy, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The photocatalytic microreactor was the most efficient, showing high organic dye photodegradation (88.4% at 12.5 mW/cm2).

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