C.V. Barros Leite

STUDY OF WORKER'S EXPOSURE TO THORIUM, URANIUM AND NIOBIUM MINERAL DUST

The aim of this study is to evaluate worker’s exposure to particles, with special attention to thorium, uranium and niobiumbearing particles. A cascade impactor (CI) with six stages was used to collect particles with aerodynamic diameter in the rangeof 0.64 to 19.4 μm. The elemental mass concentrations impacted in each stage of the CI were determined using the PIXE(Particle Induced X-ray Emission) technique. The Mass Median Aerodynamic Diameter (MMAD) and elemental mass concentration in the fine fraction of aerosol (0.5 to 2.5 μm) were determined.Personal air samplers were used by workers to collect fine particles of aerosol. The concentrations of 232Th and 228Th in these air samplers were measured by the alpha spectrometry technique. Faeces and urine samples from the workersand their wives were analyzed to determine the thorium, uranium and niobium mass concentration (mass spectrometry) and 232Th, 228Th, 238U and 234U concentrations (α spectrometry) and then compared to inhabitants of regions with low metal concentrations. The analysis of thefaecesand urine samples from workers and their wives indicated that themain pathway of thorium, uranium and niobium incorporation was byingestion. The observed concentrations of niobium and uranium inurine samples from workers showed a systemic incorporation of niobium and uranium.

PIXE and PDMS Methods Applied to Aerosols Analysis

The aim of this study was to apply the PIXE (Particle Induced X-ray Emission) and PDMS (Plasma Desorption Mass Spectrometry) techniques to characterize airborne dust particles containing metals. Aerosols generated at a mineral-sand processing plant were characterized in this study. The aerosol samples were collected at a plant that processes mineral sands to obtain rutile, ilmenite, zircon, and monazite concentrates. A cascade impactor with six stages was used to collect mineral dust particles with aerodynamic diameters in the range of 0.64 to 19.4 mum. The particles impacted on each stage of the cascade impactor were analyzed by PIXE, which permits the determination of the elemental mass air concentration and the MMAD (Mass Median Aerodynamic Diameter). The chemical compositions of the aerosol samples were identified by PDMS analysis. This study shows that, by using PIXE and PDMS techniques, it is possible to determine the chemical compounds in which the elements are associated in the aerosol particles. Based on the results of the PIXE analysis, the elemental mass concentrations and the MMADs were determined.

A cascade impactor for mineral particle analysis

ABSTRACT A cascade impactor (NCI) made of stainless steel with six stages was developed to collect particles using 50% cutpoints in the range of 0.64 to 19.4 μm. The sixth stage of the NCI was calibrated using monodisperse aerosols. The experimental MMAD (mass median aerodynamic diameter) was 0.634 μm, which agreed with the calculated MMAD. The NCI, stacked filter unit (SFU) and personal air samplers with the cyclone were used to characterize the workers exposure in two Brazilian plants where niobium minerals with thorium associated to the crystal lattice are processed. The Th, U, Nb, Zr, Pb, Fe, Sr, and Y air concentrations were determined. The MMAD of the particles containing these elements have shown the availability of mineral particles in the fine particles of aerosols. The Th concentration in the samples collected using SFU were in the same order of magnitude of those collected with the cascade impactor and are correlated.

PIXE analysis of elemental concentrations in human hair and nails

Abstract The PIXE technique was applied to examine the elemental concentrations in scalp hair and nails collected over several months from three subjects living in Rio de Janeiro, Brazil. The results were then compared with data taken from the literature, and with the range and average elemental concentrations obtained by analyzing, using the same technique and laboratory conditions, samples of scalp hair taken from 51 men and 50 women living in another region of Latin America.

Metal trace analysis by PIXE and PDMS techniques

Abstract The risk for the human health due to exposure to aerosols depends on the intake pattern, the mass concentration and the speciation of the elements present in airborne particles. In this work plasma desorption mass spectrometry (PDMS) was used as complementary technique to the particle-induced X-ray emission (PIXE) technique to characterize aerosol samples collected in the environment. The PIXE technique allows the identification of the elements present in the sample and to determine their mass concentrations. The mass spectrometry (PDMS) was used to identify the speciation of these elements present in the samples. The aerosol samples were collected using a 6-stage cascade impactor (CI) in two sites of Rio de Janeiro City. One is an island (Fundao Island) in the Guanabara Bay close to an industrial zone and the other, in Gavea, is a residential zone close to a lagoon and to the seashore. The mass median aerodynamic diameter (MMAD) measured indicated that the airborne particulates were in the fine fraction of the aerosols collected in both locations. In order to identify the contribution of the seawater particles from the Guanabara Bay in the aerosols, seawater samples were also collected at Fundao Island. The samples were analyzed by PIXE and PDMS techniques. The analysis of the results suggests that the aerosols are different in both sampling sites and also exist a contribution from the Guanabara Bay seawater particles to the aerosols collected in the Fundao Island. PIXE allows identification and quantification of the elements heavier than Na ( Z =11) while PDMS allows identification of organic and inorganic compounds present in the samples, as these techniques are used as complementary techniques they provide important information about the aerosols characterization.

Size distribution of airborne particulates in monazite dust

Abstract A six-stage cascade impactor was used to collect airborne dust particulates in the grinding area of a monazite separation plant. The samples were analysed using particle-induced X-ray emission (PIXE) to determine the elemental concentrations, with special attention to thorium and uranium concentrations. The particle size distribution of the samples containing thorium and uranium were determined. The mass median aerodynamic diameter (MMAD) obtained was 1.15 μm for both elements. The activity median aerodynamic diameter (AMAD) was estimated based on the MMAD. The results are compared with ICRP recommendations for derived air concentrations (DAC) for thorium and uranium in restricted areas.

Characterization of environmental exposure to mineral sands by PDMS technique

Abstract The risk to human health due to exposure to aerosols depends on the intake pattern, the mass concentration and the speciation of the elements present in airborne particles. In this work plasma desorption mass spectrometry (PDMS) was used to identify the speciation of metals present in the urine sample of an individual environmentally exposed to mineral sands airborne particles. Aerosol samples were collected at a Brazilian region with high concentration of mineral sands (Buena village), using a six-stage cascade impactor. The mass median aerodynamic diameter (MMAD) determined indicated that the airborne particulate was in the fine fraction of the aerosols. In order to characterize human exposure to mineral sands dust a sample from one inhabitant was analyzed by PDMS. The analysis of the results shows that the inhabitant incorporated metals from mineral sands and suggests that the source of aerosols is the mineral processing plant located at the village.

Effect of the pre-equilibrium charge state on the Li+ emission yield

Abstract The secondary emission yield of Li+ from a LiF target bombarded with 2.0 MeV nitrogen ions was measured as functions of the incident ion charge state and of the target temperature. The results were discussed considering current models (Bitensky et al., Nucl. Instr. and Meth. B 72 (1992) 380; da Silveira and Matos, Surf. Sci. 326 (1995) 370) and the effects of the contaminant layer adsorbed on the target surface. It was found that the Li+ emission yield shows a dependence on the ion pre-equilibrium charge state in contrast with the H+ emission yield, which is known to be strongly dependent on the incident charge state of the projectile.

H+ secondary ions emission stimulated by impact of energetic ions on heated target

Abstract The hydrogen secondary ion emission yield was measured for the impact of 2.0 MeV nitrogen ions on thin LiF targets using a time of flight mass spectrometer in a coincidence setup. The sample temperature was varied from 20°C up to 150°C using a resistor facing the target holder and the incident ion charge varied between 1+ and 5+. The H + relative yield measured was fitted to isothermal function allowing the determination of the adsorption heat for the hydrogen and other contaminant molecules adsorbed on the LiF target surface. The secondary H + emission process was described assuming the contribution of two different mechanisms namely potential and kinetic mechanisms and the results were discussed taking into account existing models for this ion emission process.