Haydn Barros | Universidad Simón Bolívar (original) (raw)
Papers by Haydn Barros
Geoderma, 2021
Abstract In semiarid environments, the total inorganic carbon (TIC) in soil may contribute to the... more Abstract In semiarid environments, the total inorganic carbon (TIC) in soil may contribute to the total carbon (C) pool more than the total organic C pool (TOC), thus playing a key role in storing atmospheric CO2. However, due to the different origin pathways of soil carbonates, not all of the TIC pool can be accounted for CO2 sequestration. Indeed, the inorganic C can be accounted for a net sink of CO2 only when calcium (Ca2+) forming carbonates originate from non-carbonate minerals (atmogenic inorganic C, AIC). The aim of this study carried out in a gypsiferous area is to investigate the dissolution of Ca2+ that comes from gypsum (CaSO4·2H2O) in the formation of soil atmogenic carbonates and to quantify the different forms of inorganic C pools to understand their role in storing CO2 in comparison to the TOC pool. To this end, five soil profiles were studied along a hillslope in a gypsiferous afforested area. Soil samples were analysed to determine their main chemical properties, as well as Ca2+, Sr2+, and the 87/86Sr isotopes ratios in different soil fractions. Ca2+ that comes from gypsum, which contributes to the formation of atmogenic carbonates, ranged from 0% to 63%; the remaining percentage resulted from the parent material or other sources (e.g., aeolian dust). The distribution of Ca2+ in soils depended on the relief and the distance of the soils from gypsum outcrops. The accumulation of AIC in soil developed on Holocene deposits reached a maximum accumulation of 16 kg m−3 in the first meter of depth. The average Sr2+/Ca2+ ratio in primary carbonates was 0.333, whereas it was 0.192 in secondary carbonates, thus suggesting that different sources contribute to Ca2+ in both carbonate types. Consequently, the Sr2+/Ca2+ ratio of soil carbonates could be a useful indicator of the presence of secondary carbonates. Overall, results suggest that gypsum plays a key role in the net accumulation of inorganic C in the soil, contributing to store atmospheric CO2. Finally, considering that the AIC pool was lower than the organic C pool, the latter was by far the most important element in fixing atmospheric CO2 in the soils of the semiarid Mediterranean environment that were surveyed.
We develop a method, employing Compton peak standardization and the use of matrix‐matched spiked ... more We develop a method, employing Compton peak standardization and the use of matrix‐matched spiked samples with Total Reflection X‐ray Fluorescence (TXRF), for the determination of platinum plasma concentrations of patients undergoing chemotherapy with Pt‐bearing drugs. Direct blood plasma analysis attains Pt detection limits of 70 ng/ml. Measurement results of prescribed drug doses are compared to achieved blood Pt concentrations indicating a lack of expected correlations. Direct analysis of Pt‐containing infused drugs from a variety of suppliers indicates cases of abnormal concentrations which raises quality control issues. We demonstrate the potential usefulness of the method for pharmacokinetic studies or for routine optimization and quality control of Pt chemotherapy treatments.
Radioprotection, 2005
Environmental radiation levels are modified in regions where the oil industrial activity is more ... more Environmental radiation levels are modified in regions where the oil industrial activity is more aggressive, such as in the Zulia State and the Orinoco´s Oil Belt. In these regions Venezuela is producing 1750 thousand barrels of oil from the near-to-the-surface or deep oil drilling, being its 2003 total OPEC market share 2932 thousand barrels of oil per day [1]. Petroleum constitutes an important source of energy and as the majority of natural sources it contains radionuclides and their disintegration products. The combustion of oil concentrates in the ashes those radioelements, which later enters the environment by different pathways producing adverse effects on the quality of man life. The concentration of radioelements varies greatly between oil fields, and then still requiring local survey studies in this area. Moreover due to the recent national interest in recycling processes, it becomes important to take care in the selection of materials that may contain by-products of industrial origin. In fact the oil ashes and other mining by-products are employable in the building industry. The concentration of radioactivity and heavy metals in crude oil, fuel oil Nº 6 and the ashes from power plants were determined. The analysis includes the two major thermoelectric power plants in Venezuela, Ricardo Zuluaga on the northern seaside of Caracas and Planta Centro on the littoral of Carabobo State. The study covers different samples: fuel oil N o 6, heavy and medium petroleum as well as fuel Oil N o 6 ashes. Gamma spectrometry was used for measuring 226 Ra, 214 Pb, 214 Bi, 228 Ac, 212 Pb, 212 Bi, 208 Tl and 40 K, and heavy metallic cations were determined by ICP-MS, which also allows the direct determination of 232 Th and 238 U. In this material (oil ashes) the total activity concentration is above 300 Bq.kg-1. Some criteria from the literature have been compared and used to investigate the applicability of oil ashes as an additive for building materials. The combustion concentrate also heavy metal cations, as is the case of Pb, Ni, Mn, V, Zn among others. The found high metal concentrations can represent an important environmental risk since the high amount of sulfates in the Venezuelan oil and ashes contributes to their dissolution and bioavailability.
AIP Conference Proceedings, 2010
The gamma Compton scattering over a volume of concrete has been studied in order to design an ins... more The gamma Compton scattering over a volume of concrete has been studied in order to design an instrument for density measurements. It will be used for the quality control in road construction, where large surfaces must be monitored. The experimental results and Monte Carlo simulations of the gamma Compton scattering over homogeneous and inhomogeneous volumes of concrete are shown. MC
Water Research, 2004
Dispersion of pollutants in aquatic environments depends on their uptake by suspended solids. Thi... more Dispersion of pollutants in aquatic environments depends on their uptake by suspended solids. This work deals with the uptake kinetics of 133 Ba (g-emitter and a good analogue of 226 Ra) by suspended estuarine sediments (which can be resuspended into the water column under certain conditions). This study presents a wide set of tracing experiments, including second tracing, decantation and desorption processes. The purpose is to characterize 133 Ba uptake by sediments and to investigate the use and limitations of box models in order to describe the uptake kinetics. Water and sediment samples were collected in the Huelva estuary (Spain), where environmental 226 Ra concentrations have been increased by two phosphate fertilizer industries. Samples were characterized by granulometric, organic carbon content, cation exchange capacity and XRF-EP analyses. Results revealed three-step kinetics, with characteristic times of minutes, hours and days. These results enabled the selection and calibration of a suitable box model and facilitated the testing of its use as a fully predictive tool.
Science of The Total Environment, 2004
Sediments play an important (but still poorly understood) role in the dispersion and final fate o... more Sediments play an important (but still poorly understood) role in the dispersion and final fate of radionuclides and other hazardous materials in aquatic systems. Adopting an experimental point of view, the present work deals with the transfer of a radioactive tracer from water to sediments. Sediments and waters were sampled in the Odiel and Tinto estuaries (South-West Spain) with anthropogenic-enhanced Ra concentrations. Ba was used as a tracer 226 133 since it is a gamma emitter and a good analogue of the environmental behaviour of Ra. Laboratory experiments 226 have been carried out to quantify the uptake kinetics of Ba by sediments in aqueous suspensions and by sediment 133 cores under a water column at rest. Depth distributions of Ba in sediments have been studied with different contact 133 times and using sediment samples with different grain sizes. The results reveal an important and fast uptake by suspended sediments (up to 40% in 10 min with a 20 g l suspension) and sediment cores (up to 70% in a few y1 minutes). The kinetics of the uptake by suspended sediments could be reasonably described by a model of two parallel and reversible reactions followed by a weakly-reversible reaction. The total uptake and the rate of reaction decreased with the increment of grain size. Furthermore, uptake following diffusion through the interstitial water was hardly detectable beyond 1 cm depth. For the case with more experimental results, the depth distribution could be reasonably described by the analytical solution based on the use of an effective diffusion coefficient (4.2=10 m y12 2 s) and the measured intrinsic distribution coefficient (k s63"6 l kg). y1 y1 d
Journal of Environmental Radioactivity, 2004
Modern nuclear metrological tools allow the remote surveillance of the radiological status of the... more Modern nuclear metrological tools allow the remote surveillance of the radiological status of the aquatic systems, providing an important advance in the protection of the environment. Nevertheless, the significance of the radiological data could be highly improved through simultaneous recording of physical and chemical variables that govern the behaviour and bioavailability of radionuclides in these aquatic systems. This work reviews some of these variables from the point of view of the environmental modelling. The amount, nature and dynamics of the suspended loads and bottom sediments strongly influence the behaviour of particle-reactive radionuclides. The kinetics of this process has a very fast component, as it is shown from our recent studies with 241Am, 239Pu and 133Ba in several aquatic systems from southern Spain. Changes in pH, temperature and in the electrical conductivity are influencing the uptake kinetics and the final partitioning of the radioactivity. Water currents govern the radionuclide transport and dispersion. These points are illustrated with modelling exercises in the scenarios of the Suez Canal (Egypt) and the Härsvatten Lake (Sweden).
Ecological Modelling, 2005
The uptake of radionuclides and heavy metals by suspended particulate matter (SPM) features chara... more The uptake of radionuclides and heavy metals by suspended particulate matter (SPM) features characteristic times, which actually affect the transport, bioavailability and the final fate of such substances in aquatic ecosystems. Box models represent a useful approach to study this process. Based upon constant reaction rates, they are developed and calibrated from batch experiments. Considerable discrepancy is found in the structure of the proposed multi-reaction models, while traditional experiments cannot account for the intimate detail of the uptake mechanisms. This paper demonstrates that apparently different models are, nevertheless, mathematically equivalent, thereby questioning the physical meaning of transfer coefficients. The mathematical demonstration is a straightforward consequence of the methodology in general use. The equivalence is preserved, for closed and open systems, even if modifications are made to parameters which affect the bioavailability of those pollutants in aquatic environments: SPM concentrations, specific surface area and concentration of competitive ions. Furthermore, the possibilities for further research are discussed since this equivalence can be broken by changes in temperature.
Interciencias
El PNMC posee una alta densidad de yacimientos arqueológicos que atestiguan los patrones de ocupa... more El PNMC posee una alta densidad de yacimientos arqueológicos que atestiguan los patrones de ocupación del territorio por parte de los caquetíos. Son pocos los estudios sobre la cultura material y hasta ahora no existían estudios fisicoquímicos de los yacimientos, que dieran luces sobre la intensidad de ocupación prehispánica, durante el contacto y en las décadas subsiguientes. En este trabajo se presenta la caracterización cultural de dos áreas de recolección (MCa/1-9 y MCa/10-20) y los análisis fisicoquímicos de suelo en una de ellas (MCa/1-9). Las áreas de recolección abarcan 5 y 1,8 ha, separadas por una distancia de 800 m. Ambas contienen materiales cerámicos de estilo Dabajuroide, arcilla sin procesar, conchas de moluscos, carbón vegetal y artefactos líticos, característicos de los asentamientos de los siglos XIV-XVIII. MCa/10-20 posee fragmentos cerámicos de mayor tamaño, con piezas de uso desde utilitario hasta ritual, con evidencias de elaboración in situ de alfarería. En MC...
AIP Conference Proceedings, 2009
Science of The Total Environment, 2004
Sediments play an important (but still poorly understood) role in the dispersion and final fate o... more Sediments play an important (but still poorly understood) role in the dispersion and final fate of radionuclides and other hazardous materials in aquatic systems. Adopting an experimental point of view, the present work deals with the transfer of a radioactive tracer from water to sediments. Sediments and waters were sampled in the Odiel and Tinto estuaries (South-West Spain) with anthropogenic-enhanced 226Ra concentrations. 133Ba was used as a tracer since it is a gamma emitter and a good analogue of the environmental behaviour of 226Ra. Laboratory experiments have been carried out to quantify the uptake kinetics of 133Ba by sediments in aqueous suspensions and by sediment cores under a water column at rest. Depth distributions of 133Ba in sediments have been studied with different contact times and using sediment samples with different grain sizes. The results reveal an important and fast uptake by suspended sediments (up to 40% in 10 min with a 20 g l−1 suspension) and sediment c...
We report experimental results of the pattern developed by a mixture of two types of grains in a ... more We report experimental results of the pattern developed by a mixture of two types of grains in a triangular rotating tumbler operating in the avalanche regime. At the centroid of the triangular tumbler an invariant zone appears where the grains do not move relative to the tumbler. We characterize this invariant zone by its normalized area, A_i, and its circularity index as a function of the normalized filling area A. We find a critical filling area so that only for A>A_c invariant zones are obtained. These zones scale as A_i∼ (A-A_c)^2 near A_c. We have obtained a maximum in the circularity index for A≈ 0.8, for which the shape of the invariant zone is closer to a circular one. The experimental results are reproduced by a simple model which, based on the surface position, accounts for all the possible straight lines within the triangle that satisfy the condition of constant A. We have obtained an analytic expression for the contour of the invariant zone.
A compact and modern equipment for fast neutron and γ-ray transmission (FNGT) technique has been ... more A compact and modern equipment for fast neutron and γ-ray transmission (FNGT) technique has been developed. The FNGT is used to perform non-destructive analysis of samples and it makes use of R-ratio that is the ratio of absorption coefficients of fast neutrons and gamma-rays [1]. The FNGT technique has a very good resolving power to determine the average atomic number of compounds with low atomic number (Z<13). Crude oil lays in this range of values, therefore we suggest to employ the mentioned technique for monitoring sulfur content in oil-business. The on-line analysis of fluid provides knowledge of sulfur content that has positive effects on the refinery plant. Nowadays, the used technique requires 7-10 days of delay in getting the information due the offline chemical or nuclear analysis. The compact system makes use of a Cf-252 source, a single liquid scintillator detector EJ-301 with neutron/gamma discrimination capabilities and a modern nuclear electronics based on fast di...
Se determinaron las concentraciones de U, Th, K (in situ y en laboratorio) y radon (activo y pasi... more Se determinaron las concentraciones de U, Th, K (in situ y en laboratorio) y radon (activo y pasivo) en una zona del campo petrolero Tascabana, Estado Anzoategui. En esa region se habia detectado gas natural durante la perforacion de pozos de agua y desde hace varios anos se producen emanaciones de gas natural en el rio de la localidad. A partir de los mapas radiometricos se identificaron las areas donde se producen filtraciones de hidrocarburos. Se demostro que los valores anomalos (altos) de radon en los gases del suelo no estan relacionados con acumulacion superficial de su progenitor, sino mas bien a su transporte por otros gases. Los mapas de concentraciones de radon y K mostraron valores anomalos (altos y bajos, respectivamente) cerca de las emanaciones de gas en el rio. La region con valores anomalos se extiende hacia los sitios donde se detecto gas natural en pozos de agua. La zona donde se detectaron las mayores concentraciones de 222Rn, y menores de K, parece indicar la pr...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Recent Advances in Multidisciplinary Applied Physics, 2005
Abstract Considerable efforts have been devoted to experimental studies on the sorption kinetics ... more Abstract Considerable efforts have been devoted to experimental studies on the sorption kinetics and the transport of radionuclides in porous media. Motivations: their environmental impact, selection of materials for nuclear waste deposits and pollution in underground aquifers. The present study investigates aspects of non-conservative radionuclide’s dispersion and sorption kinetics in natural sediments. Waters and sediments were sampled in two different environments. It was investigated the uptake kinetics of 133Ba by sediments in aqueous suspensions and cores. Samples from the upper most layer (estuary) reveals an important and fast uptake by sediment cores. The depth distribution could be reasonably described by means of an effective diffusion coefficient. The uptake kinetics by suspended sediments could be described by a compartmental kinetic model, but the effective diffusion model (based in a distribution coefficient) shows serious limitations to describe the profiles along the time.
First International Meeting for Applied Geoscience & Energy Expanded Abstracts
Coltan is one of the main ores for obtaining tantalum and niobium, two elements with very particu... more Coltan is one of the main ores for obtaining tantalum and niobium, two elements with very particular physicochemical characteristics and of great interest for technological development since the 20th century (Hughes et al. 2011). The concentrations of uranium and thorium in Venezuelan coltan samples, previously measured by the Nuclear Physics Laboratory of the Simón Bolívar University (LFN-USB), and the description of some alluvial deposits in the Parguaza region (South of Venezuela) show the potential feasibility of locating superficial mineral deposits using gamma ray spectrometry by mapping the radiation associated with U and Th contained in these minerals. In this work we explore this possibility by using a high-density scintillator detector (BGO 3"x3" Crismatec Scintibloc 76S76). Coltan samples were used on a test field conditioned to emulate a shallow alluvial deposit, as those observed in some areas of the Parguaza region, obtaining that for detailed prospecting a 2.5x2.5 m 2 spaced survey grid using a BGO detector is effective in detecting significant quantities of coltan (kilograms), even at a depth of 40 cm (depth at which artisanal extractions have been described in recent years). The need to prioritize the quantification of thorium and especially uranium was also evidenced, using their more energetic emission lines.
Geoderma, 2021
Abstract In semiarid environments, the total inorganic carbon (TIC) in soil may contribute to the... more Abstract In semiarid environments, the total inorganic carbon (TIC) in soil may contribute to the total carbon (C) pool more than the total organic C pool (TOC), thus playing a key role in storing atmospheric CO2. However, due to the different origin pathways of soil carbonates, not all of the TIC pool can be accounted for CO2 sequestration. Indeed, the inorganic C can be accounted for a net sink of CO2 only when calcium (Ca2+) forming carbonates originate from non-carbonate minerals (atmogenic inorganic C, AIC). The aim of this study carried out in a gypsiferous area is to investigate the dissolution of Ca2+ that comes from gypsum (CaSO4·2H2O) in the formation of soil atmogenic carbonates and to quantify the different forms of inorganic C pools to understand their role in storing CO2 in comparison to the TOC pool. To this end, five soil profiles were studied along a hillslope in a gypsiferous afforested area. Soil samples were analysed to determine their main chemical properties, as well as Ca2+, Sr2+, and the 87/86Sr isotopes ratios in different soil fractions. Ca2+ that comes from gypsum, which contributes to the formation of atmogenic carbonates, ranged from 0% to 63%; the remaining percentage resulted from the parent material or other sources (e.g., aeolian dust). The distribution of Ca2+ in soils depended on the relief and the distance of the soils from gypsum outcrops. The accumulation of AIC in soil developed on Holocene deposits reached a maximum accumulation of 16 kg m−3 in the first meter of depth. The average Sr2+/Ca2+ ratio in primary carbonates was 0.333, whereas it was 0.192 in secondary carbonates, thus suggesting that different sources contribute to Ca2+ in both carbonate types. Consequently, the Sr2+/Ca2+ ratio of soil carbonates could be a useful indicator of the presence of secondary carbonates. Overall, results suggest that gypsum plays a key role in the net accumulation of inorganic C in the soil, contributing to store atmospheric CO2. Finally, considering that the AIC pool was lower than the organic C pool, the latter was by far the most important element in fixing atmospheric CO2 in the soils of the semiarid Mediterranean environment that were surveyed.
We develop a method, employing Compton peak standardization and the use of matrix‐matched spiked ... more We develop a method, employing Compton peak standardization and the use of matrix‐matched spiked samples with Total Reflection X‐ray Fluorescence (TXRF), for the determination of platinum plasma concentrations of patients undergoing chemotherapy with Pt‐bearing drugs. Direct blood plasma analysis attains Pt detection limits of 70 ng/ml. Measurement results of prescribed drug doses are compared to achieved blood Pt concentrations indicating a lack of expected correlations. Direct analysis of Pt‐containing infused drugs from a variety of suppliers indicates cases of abnormal concentrations which raises quality control issues. We demonstrate the potential usefulness of the method for pharmacokinetic studies or for routine optimization and quality control of Pt chemotherapy treatments.
Radioprotection, 2005
Environmental radiation levels are modified in regions where the oil industrial activity is more ... more Environmental radiation levels are modified in regions where the oil industrial activity is more aggressive, such as in the Zulia State and the Orinoco´s Oil Belt. In these regions Venezuela is producing 1750 thousand barrels of oil from the near-to-the-surface or deep oil drilling, being its 2003 total OPEC market share 2932 thousand barrels of oil per day [1]. Petroleum constitutes an important source of energy and as the majority of natural sources it contains radionuclides and their disintegration products. The combustion of oil concentrates in the ashes those radioelements, which later enters the environment by different pathways producing adverse effects on the quality of man life. The concentration of radioelements varies greatly between oil fields, and then still requiring local survey studies in this area. Moreover due to the recent national interest in recycling processes, it becomes important to take care in the selection of materials that may contain by-products of industrial origin. In fact the oil ashes and other mining by-products are employable in the building industry. The concentration of radioactivity and heavy metals in crude oil, fuel oil Nº 6 and the ashes from power plants were determined. The analysis includes the two major thermoelectric power plants in Venezuela, Ricardo Zuluaga on the northern seaside of Caracas and Planta Centro on the littoral of Carabobo State. The study covers different samples: fuel oil N o 6, heavy and medium petroleum as well as fuel Oil N o 6 ashes. Gamma spectrometry was used for measuring 226 Ra, 214 Pb, 214 Bi, 228 Ac, 212 Pb, 212 Bi, 208 Tl and 40 K, and heavy metallic cations were determined by ICP-MS, which also allows the direct determination of 232 Th and 238 U. In this material (oil ashes) the total activity concentration is above 300 Bq.kg-1. Some criteria from the literature have been compared and used to investigate the applicability of oil ashes as an additive for building materials. The combustion concentrate also heavy metal cations, as is the case of Pb, Ni, Mn, V, Zn among others. The found high metal concentrations can represent an important environmental risk since the high amount of sulfates in the Venezuelan oil and ashes contributes to their dissolution and bioavailability.
AIP Conference Proceedings, 2010
The gamma Compton scattering over a volume of concrete has been studied in order to design an ins... more The gamma Compton scattering over a volume of concrete has been studied in order to design an instrument for density measurements. It will be used for the quality control in road construction, where large surfaces must be monitored. The experimental results and Monte Carlo simulations of the gamma Compton scattering over homogeneous and inhomogeneous volumes of concrete are shown. MC
Water Research, 2004
Dispersion of pollutants in aquatic environments depends on their uptake by suspended solids. Thi... more Dispersion of pollutants in aquatic environments depends on their uptake by suspended solids. This work deals with the uptake kinetics of 133 Ba (g-emitter and a good analogue of 226 Ra) by suspended estuarine sediments (which can be resuspended into the water column under certain conditions). This study presents a wide set of tracing experiments, including second tracing, decantation and desorption processes. The purpose is to characterize 133 Ba uptake by sediments and to investigate the use and limitations of box models in order to describe the uptake kinetics. Water and sediment samples were collected in the Huelva estuary (Spain), where environmental 226 Ra concentrations have been increased by two phosphate fertilizer industries. Samples were characterized by granulometric, organic carbon content, cation exchange capacity and XRF-EP analyses. Results revealed three-step kinetics, with characteristic times of minutes, hours and days. These results enabled the selection and calibration of a suitable box model and facilitated the testing of its use as a fully predictive tool.
Science of The Total Environment, 2004
Sediments play an important (but still poorly understood) role in the dispersion and final fate o... more Sediments play an important (but still poorly understood) role in the dispersion and final fate of radionuclides and other hazardous materials in aquatic systems. Adopting an experimental point of view, the present work deals with the transfer of a radioactive tracer from water to sediments. Sediments and waters were sampled in the Odiel and Tinto estuaries (South-West Spain) with anthropogenic-enhanced Ra concentrations. Ba was used as a tracer 226 133 since it is a gamma emitter and a good analogue of the environmental behaviour of Ra. Laboratory experiments 226 have been carried out to quantify the uptake kinetics of Ba by sediments in aqueous suspensions and by sediment 133 cores under a water column at rest. Depth distributions of Ba in sediments have been studied with different contact 133 times and using sediment samples with different grain sizes. The results reveal an important and fast uptake by suspended sediments (up to 40% in 10 min with a 20 g l suspension) and sediment cores (up to 70% in a few y1 minutes). The kinetics of the uptake by suspended sediments could be reasonably described by a model of two parallel and reversible reactions followed by a weakly-reversible reaction. The total uptake and the rate of reaction decreased with the increment of grain size. Furthermore, uptake following diffusion through the interstitial water was hardly detectable beyond 1 cm depth. For the case with more experimental results, the depth distribution could be reasonably described by the analytical solution based on the use of an effective diffusion coefficient (4.2=10 m y12 2 s) and the measured intrinsic distribution coefficient (k s63"6 l kg). y1 y1 d
Journal of Environmental Radioactivity, 2004
Modern nuclear metrological tools allow the remote surveillance of the radiological status of the... more Modern nuclear metrological tools allow the remote surveillance of the radiological status of the aquatic systems, providing an important advance in the protection of the environment. Nevertheless, the significance of the radiological data could be highly improved through simultaneous recording of physical and chemical variables that govern the behaviour and bioavailability of radionuclides in these aquatic systems. This work reviews some of these variables from the point of view of the environmental modelling. The amount, nature and dynamics of the suspended loads and bottom sediments strongly influence the behaviour of particle-reactive radionuclides. The kinetics of this process has a very fast component, as it is shown from our recent studies with 241Am, 239Pu and 133Ba in several aquatic systems from southern Spain. Changes in pH, temperature and in the electrical conductivity are influencing the uptake kinetics and the final partitioning of the radioactivity. Water currents govern the radionuclide transport and dispersion. These points are illustrated with modelling exercises in the scenarios of the Suez Canal (Egypt) and the Härsvatten Lake (Sweden).
Ecological Modelling, 2005
The uptake of radionuclides and heavy metals by suspended particulate matter (SPM) features chara... more The uptake of radionuclides and heavy metals by suspended particulate matter (SPM) features characteristic times, which actually affect the transport, bioavailability and the final fate of such substances in aquatic ecosystems. Box models represent a useful approach to study this process. Based upon constant reaction rates, they are developed and calibrated from batch experiments. Considerable discrepancy is found in the structure of the proposed multi-reaction models, while traditional experiments cannot account for the intimate detail of the uptake mechanisms. This paper demonstrates that apparently different models are, nevertheless, mathematically equivalent, thereby questioning the physical meaning of transfer coefficients. The mathematical demonstration is a straightforward consequence of the methodology in general use. The equivalence is preserved, for closed and open systems, even if modifications are made to parameters which affect the bioavailability of those pollutants in aquatic environments: SPM concentrations, specific surface area and concentration of competitive ions. Furthermore, the possibilities for further research are discussed since this equivalence can be broken by changes in temperature.
Interciencias
El PNMC posee una alta densidad de yacimientos arqueológicos que atestiguan los patrones de ocupa... more El PNMC posee una alta densidad de yacimientos arqueológicos que atestiguan los patrones de ocupación del territorio por parte de los caquetíos. Son pocos los estudios sobre la cultura material y hasta ahora no existían estudios fisicoquímicos de los yacimientos, que dieran luces sobre la intensidad de ocupación prehispánica, durante el contacto y en las décadas subsiguientes. En este trabajo se presenta la caracterización cultural de dos áreas de recolección (MCa/1-9 y MCa/10-20) y los análisis fisicoquímicos de suelo en una de ellas (MCa/1-9). Las áreas de recolección abarcan 5 y 1,8 ha, separadas por una distancia de 800 m. Ambas contienen materiales cerámicos de estilo Dabajuroide, arcilla sin procesar, conchas de moluscos, carbón vegetal y artefactos líticos, característicos de los asentamientos de los siglos XIV-XVIII. MCa/10-20 posee fragmentos cerámicos de mayor tamaño, con piezas de uso desde utilitario hasta ritual, con evidencias de elaboración in situ de alfarería. En MC...
AIP Conference Proceedings, 2009
Science of The Total Environment, 2004
Sediments play an important (but still poorly understood) role in the dispersion and final fate o... more Sediments play an important (but still poorly understood) role in the dispersion and final fate of radionuclides and other hazardous materials in aquatic systems. Adopting an experimental point of view, the present work deals with the transfer of a radioactive tracer from water to sediments. Sediments and waters were sampled in the Odiel and Tinto estuaries (South-West Spain) with anthropogenic-enhanced 226Ra concentrations. 133Ba was used as a tracer since it is a gamma emitter and a good analogue of the environmental behaviour of 226Ra. Laboratory experiments have been carried out to quantify the uptake kinetics of 133Ba by sediments in aqueous suspensions and by sediment cores under a water column at rest. Depth distributions of 133Ba in sediments have been studied with different contact times and using sediment samples with different grain sizes. The results reveal an important and fast uptake by suspended sediments (up to 40% in 10 min with a 20 g l−1 suspension) and sediment c...
We report experimental results of the pattern developed by a mixture of two types of grains in a ... more We report experimental results of the pattern developed by a mixture of two types of grains in a triangular rotating tumbler operating in the avalanche regime. At the centroid of the triangular tumbler an invariant zone appears where the grains do not move relative to the tumbler. We characterize this invariant zone by its normalized area, A_i, and its circularity index as a function of the normalized filling area A. We find a critical filling area so that only for A>A_c invariant zones are obtained. These zones scale as A_i∼ (A-A_c)^2 near A_c. We have obtained a maximum in the circularity index for A≈ 0.8, for which the shape of the invariant zone is closer to a circular one. The experimental results are reproduced by a simple model which, based on the surface position, accounts for all the possible straight lines within the triangle that satisfy the condition of constant A. We have obtained an analytic expression for the contour of the invariant zone.
A compact and modern equipment for fast neutron and γ-ray transmission (FNGT) technique has been ... more A compact and modern equipment for fast neutron and γ-ray transmission (FNGT) technique has been developed. The FNGT is used to perform non-destructive analysis of samples and it makes use of R-ratio that is the ratio of absorption coefficients of fast neutrons and gamma-rays [1]. The FNGT technique has a very good resolving power to determine the average atomic number of compounds with low atomic number (Z<13). Crude oil lays in this range of values, therefore we suggest to employ the mentioned technique for monitoring sulfur content in oil-business. The on-line analysis of fluid provides knowledge of sulfur content that has positive effects on the refinery plant. Nowadays, the used technique requires 7-10 days of delay in getting the information due the offline chemical or nuclear analysis. The compact system makes use of a Cf-252 source, a single liquid scintillator detector EJ-301 with neutron/gamma discrimination capabilities and a modern nuclear electronics based on fast di...
Se determinaron las concentraciones de U, Th, K (in situ y en laboratorio) y radon (activo y pasi... more Se determinaron las concentraciones de U, Th, K (in situ y en laboratorio) y radon (activo y pasivo) en una zona del campo petrolero Tascabana, Estado Anzoategui. En esa region se habia detectado gas natural durante la perforacion de pozos de agua y desde hace varios anos se producen emanaciones de gas natural en el rio de la localidad. A partir de los mapas radiometricos se identificaron las areas donde se producen filtraciones de hidrocarburos. Se demostro que los valores anomalos (altos) de radon en los gases del suelo no estan relacionados con acumulacion superficial de su progenitor, sino mas bien a su transporte por otros gases. Los mapas de concentraciones de radon y K mostraron valores anomalos (altos y bajos, respectivamente) cerca de las emanaciones de gas en el rio. La region con valores anomalos se extiende hacia los sitios donde se detecto gas natural en pozos de agua. La zona donde se detectaron las mayores concentraciones de 222Rn, y menores de K, parece indicar la pr...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Recent Advances in Multidisciplinary Applied Physics, 2005
Abstract Considerable efforts have been devoted to experimental studies on the sorption kinetics ... more Abstract Considerable efforts have been devoted to experimental studies on the sorption kinetics and the transport of radionuclides in porous media. Motivations: their environmental impact, selection of materials for nuclear waste deposits and pollution in underground aquifers. The present study investigates aspects of non-conservative radionuclide’s dispersion and sorption kinetics in natural sediments. Waters and sediments were sampled in two different environments. It was investigated the uptake kinetics of 133Ba by sediments in aqueous suspensions and cores. Samples from the upper most layer (estuary) reveals an important and fast uptake by sediment cores. The depth distribution could be reasonably described by means of an effective diffusion coefficient. The uptake kinetics by suspended sediments could be described by a compartmental kinetic model, but the effective diffusion model (based in a distribution coefficient) shows serious limitations to describe the profiles along the time.
First International Meeting for Applied Geoscience & Energy Expanded Abstracts
Coltan is one of the main ores for obtaining tantalum and niobium, two elements with very particu... more Coltan is one of the main ores for obtaining tantalum and niobium, two elements with very particular physicochemical characteristics and of great interest for technological development since the 20th century (Hughes et al. 2011). The concentrations of uranium and thorium in Venezuelan coltan samples, previously measured by the Nuclear Physics Laboratory of the Simón Bolívar University (LFN-USB), and the description of some alluvial deposits in the Parguaza region (South of Venezuela) show the potential feasibility of locating superficial mineral deposits using gamma ray spectrometry by mapping the radiation associated with U and Th contained in these minerals. In this work we explore this possibility by using a high-density scintillator detector (BGO 3"x3" Crismatec Scintibloc 76S76). Coltan samples were used on a test field conditioned to emulate a shallow alluvial deposit, as those observed in some areas of the Parguaza region, obtaining that for detailed prospecting a 2.5x2.5 m 2 spaced survey grid using a BGO detector is effective in detecting significant quantities of coltan (kilograms), even at a depth of 40 cm (depth at which artisanal extractions have been described in recent years). The need to prioritize the quantification of thorium and especially uranium was also evidenced, using their more energetic emission lines.