Concentrations of Cr, Co, Ni, Cu, Zn, Pb and Fe in the topsoils (0-10 cm) from Las Tunas city were measured by X-ray fluorescence analysis. The mean Cr, Co, Ni, Cu, Zn and Pb contents in the urban topsoil samples (97 ± 30, 14 ± 2, 35 ± 36, 94 ± 26, 199 ± 87 and 42 ± 29 mg kg⁻¹ dry weight, respectively) were compared with mean concentrations for other cities around the world with similar population. Cr content in school grounds, parks and residential areas exceed in 20 % the average Cr background level. Highest content for Ni was determined in residential areas, for Zn in market gardens soils and as for Pb, the highest topsoil-background content ratios were observed for market gardens (2.7) and residential areas (2.3). Spatial distribution maps indicated the same behaviour for Cr-Co-Ni and Pb-Zn, respectively, whereas the spatial distribution of Cu differs from other heavy metals. On the other hand, the metal-to-iron normalisation, using (10-20 cm) bottom soil contents as background, showed that topsoils in Las Tunas city are severely enriched with lead and not enriched with the rest of the determined metals. The average values of integrated pollution index (IPI) indicated that soils are moderately contaminated by heavy metals (1.17 ≤ IPI(ave) ≤ 1.39), but enrichment index values shows that metal concentrations on the studied locations are not above the permissible levels for urban agriculture.

Levels of iron, copper, zinc and lead were determined in sediments and soft tissue of the oyster Crassostrea rhizophorae collected from Guacanayabo Gulf, Cuba. Metal-to-Iron ratio in sediments shows an average enrichment for Cu (5,1), Pb (11,7) and Zn (1,3) in the last 20 years. Metal concentrations found in soft tissue of C. rhizophorae are site dependent. The average biota-sediment accumulation factors (BSAFs) obtained for Fe, Cu and Pb are less than unity in all cases, indicating that only a little fraction of Cu and Pb in the sediments is bioavailable, independently of their enrichments. Zinc has an average BSAF value of 2.4 and may represent a serious impact in the area. The concentrations of zinc and copper in some of the oysters are above typical public health recommended limits.

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Iron, chromium, cobalt and nickel concentration levels in urban soil samples collected from Moa city (Holguín province), northeastern Cuba were determined. Both chromium and nickel contents exceed the Dutch Intervention Value soil quality standard in 2.8-5.4 and 1.3-3.3 times, respectively. Furthermore, cobalt content exceeds the Target Value in 1.3-1.8 times. Metal-to-Iron normalization predicts a natural origin for nickel and cobalt (Enrichment Factor <1), and also a moderate chromium enrichment (Enrichment Factor = 1.5-4.0) in all studied stations. The application of the Urban Environment Entropy Model show that residential area located near to industrial area is slightly affected by industrial chromium emissions and not affected by cobalt and nickel possible emissions. A chromium speciation in soil samples is recommended in order to evaluate the real impact of the current chromium content in Moa urban soils to local urban and suburban agricultures.

The results of the first experiments carried out in the new electron accelerator of the Linear Accelerator Laboratory (LAL) of the Physics Institute of Universidade de São Paulo are reported here. A 1.9 MeV beam line, which allows the use of the injector beam for experimental physics, was added to the original accelerator design. Electron bremsstrahlung spectra for Ag and Au thin targets observed at 30 o and 60 o with respect to the beam direction were collected in a HPGe coaxial detector, whose dimensions, including crystal inner hole dimensions and dead layer thickness, were estimated by means of combined experimental measurements and Monte Carlo simulations with the MCNP code, to evaluate the detector response function to perform the deconvolution of the spectrum. Cross sections for bremsstrahlung yield were determined for the entire measured energy range (100-1910 keV) and for the tip region (1700-1970 keV). The results in the tip region are in agreement with MCNPX and PENELOPE predictions. The possible causes for the disagreement at energies lower than 1800 keV are discussed. The design of a Nuclear Resonance Fluorescence (NRF) setup, aiming the study of dipolar excitations in nuclei with bremsstrahlung photons when the Microtron electron energy reaches 10 MeV, is also shown. The setup was designed with the characteristics of the Microtron building and facilities in mind, and searches to minimize the radiation caused by scattered photons and neutrons from photonuclear reactions. The behavior of the NRF setup elements: converter, collimator, detector shielding and photon beam dump, were studied by simulation as functions of their characteristics-dimensions, shapes, materials-using the MCNPX code. The spectral intensity to be observed by the photon detector in the designed NRF setup with a 27 Al reference target, typical for NRF measurements, was assessed by simulation and shows the feasibility of this sort of experiment with the Microtron. vi vii Dedicatória A minha tia Haydee, a meus pais Lucy, Aldo e Rodolfo, a meu amor Fátima, e à maior alegria de minha vida, Marquitos... A mi tía Haydee, a mis padres Lucy, Aldo y Rodolfo, a mi amor Fátima, y a la mayor alegría de mi vida, Marquitos… viii ix Agradecimentos À Prof. Nora pelos prazos estendidos, pela ajuda insuperável em muitas coisas alem do doutorado, por fazer deste trabalho quase seu segundo Phd., sem ela simplesmente eu não estaria escrevendo estes agradecimentos, Ao Prof. Vito pela linha de baixa energia, pelas correções e sugestões e pelo grande tempo dedicado, A Vicky, sempre agradecido, sem ela para mi o Brasil, fora o carnaval de Rio, as brigas no vôlei das cubanas e as brasileiras..., mas só na TV, Ao Prof. Marcos, meu primeiro orientador, sempre exigente, preciso e disposto a ajudar, A Alexandre e Alfredo por fazerem o Microtron funcionar, por conseguirem superar as múltiplas inconveniências, A Roberto e ao pessoal da oficina mecânica, sempre ágeis e atentos, À Wanda Gabriel Pereira Engel do LAFN pelo preparo dos alvos, À Prof. Márcia de Almeida ...