RESUMO
Cosmogenic 7Be was used to evaluate soil loss in a mountainous micro-watershed near Belo Horizonte, Southwest Brazil. Two nearby sites were selected, a reference site in a flat area and an eroded site in a hill slope. At the reference site, soil samples were collected monthly throughout the year in order to evaluate seasonal variations of 7Be inventory in soil and its relation with the precipitation regime. Additionally, rainwater was collected and the expected 7Be soil content was predicted. At the reference site, the 7Be inventory shows seasonal variations, in accordance with the rainy season, and its distribution in the soil profile shows an exponential decrease in depth (h0 = 6.9 ± 0.6 kg m-2; r2 = 0.97). At the eroded site, two soil sampling campaigns were performed in order to measure soil erosion in the watershed. The estimated net erosion was 42.2 ± 3.7 t ha-1, indicating the loss of upper 5mm of soil per year. This corresponds to soil losses in the area in the range from moderate to severe erosion.
Assuntos
Berílio/análise , Radioisótopos/análise , Erosão do Solo , Brasil , Chuva , Solo/químicaRESUMO
In Chile, erosion processes (on-site and off-site impact) affect at least 36.9 million ha-1, representing 49% of the total land area. Different regions show severe soil degradation mainly caused by water erosion processes. The importance of sediment-associated transport and the key role of soil erosion affect the fertility of the land and the contamination of water bodies. The aim of this work was to estimate the erosion rate, caused by the rainfall in Apalta vineyards in the Libertador General Bernardo O'Higgins Region of Chile using isotope techniques, assessing the 7Be runoff during four years (2009-2012). The 7Be distribution mass depth at a reference site ranged from 7 to 24â kgâ m-2 in the first two centimetres soil layer. Even when the vineyards have been well managed, the topographic characteristics and the climatic conditions facilitated soil erosion, with average rates of 50.4, 23.5, 50.6 and 67.3 tons ha-1 y-1 in 2009, 2010, 2011 and 2012, respectively. The robustness of the 7Be technique demonstrated the advantage of a non-soil-destructive methodology to calculate soil distribution and erosion rates.
Assuntos
Berílio/análise , Monitoramento Ambiental/métodos , Fazendas , Radioisótopos/análise , Chuva/química , Solo/química , Movimentos da Água , ChileRESUMO
A long counter detector was manufactured by the Institute of Advanced Studies (IEAV) and was characterised in the neutron low scattering room at Brazilian National Ionising Radiation Metrology Laboratory (LNMRI/IRD) to deploy a secondary Standard for neutron fluence. The effective centre was measured experimentally with 252Cf+D2O, 252Cf, 241AmBe and 238PuBe neutron sources, having average energies from 0.55 to 4.16 MeV. The experimental arrangement and detector construction were carefully reproduced in Monte Carlo simulations, and the computational results were found to be in good agreement with those from experiment.
Assuntos
Amerício/normas , Berílio/normas , Califórnio/normas , Laboratórios/normas , Nêutrons , Plutônio/normas , Monitoramento de Radiação/normas , Proteção Radiológica/normas , Amerício/análise , Berílio/análise , Calibragem , Califórnio/análise , Método de Monte Carlo , Plutônio/análise , Doses de RadiaçãoRESUMO
Occupational neutron fields usually have energies from the thermal range to some MeV and the characterization of the spectra is essential for estimation of the radioprotection quantities. Thus, the spectrum must be unfolded based on a limited number of measurements. This study implemented an algorithm based on the bee colonies behavior, named Artificial Bee Colony (ABC), where the intelligent behavior of the bees in search of food is reproduced to perform the unfolding of neutron spectra. The experimental measurements used Bonner spheres and 6LiI (Eu) detector, with irradiations using a thermal neutron flux and three reference fields: 241Am-Be, 252Cf and 252Cf (D2O). The ABC obtained good estimation of the expected spectrum even without previous information and its results were closer to expected spectra than those obtained by the SPUNIT algorithm.
Assuntos
Algoritmos , Comportamento Apetitivo , Abelhas , Nêutrons , Monitoramento de Radiação/instrumentação , Proteção Radiológica/instrumentação , Amerício/análise , Animais , Berílio/análise , Biomimética , Califórnio/análise , Simulação por Computador , Método de Monte Carlo , Doses de Radiação , Monitoramento de Radiação/métodosRESUMO
This study describes the use of a neutron irradiator system based on a plutonium-beryllium neutron source for MnSO4 solution activation for use to determine the MSB system efficiency. Computational simulations using Monte Carlo code were performed to establish the main characteristics of the irradiator system. Among the simulated geometries and volumes, semi-cylindrical shape with 84.5 cm3 of MnSO4 solution yielded the best option to be built. Activity measurements were performed with a high-pure germanium detector to validate the new irradiation system. Results showed an average efficiency and uncertainty of the experimental standard deviation of the mean: 5.742 × 10-4 ± 0.036 × 10-4 (coverage factor k = 1), for MSB system. Efficiency value obtained shows good correlation to other published methods (i.e. a relative difference of 0.07%). This alternative metrological method demonstrated the utility of neutron sources for the irradiation of solutions in metrology laboratories providing a cost-efficient alternative to nuclear reactors or particle accelerators.
Assuntos
Berílio/análise , Compostos de Manganês/química , Nêutrons , Plutônio/análise , Monitoramento de Radiação/instrumentação , Sulfatos/química , Calibragem , Método de Monte Carlo , Doses de RadiaçãoRESUMO
The standard thermal neutron flux unit, TNF2, in the Brazilian National Ionizing Radiation Metrology Laboratory was rebuilt. Fluence is still achieved by moderating of four 241Am-Be sources with 0.6 TBq each. The facility was again simulated and redesigned with graphite core and paraffin added graphite blocks surrounding it. Simulations using the MCNPX code on different geometric arrangements of moderator materials and neutron sources were performed. The resulting neutron fluence quality in terms of intensity, spectrum and cadmium ratio was evaluated. After this step, the system was assembled based on the results obtained from the simulations and measurements were performed with equipment existing in LNMRI/IRD and by simulated equipment. This work focuses on the characterization of a central chamber point and external points around the TNF2 in terms of neutron spectrum, fluence and ambient dose equivalent, H*(10). This system was validated with spectra measurements, fluence and H*(10) to ensure traceability.
Assuntos
Amerício/normas , Berílio/normas , Laboratórios/normas , Nêutrons , Monitoramento de Radiação/normas , Proteção Radiológica/normas , Amerício/análise , Berílio/análise , Calibragem , Método de Monte Carlo , Doses de RadiaçãoRESUMO
Beryllium-7 (7Be) is a natural radionuclide of cosmogenic origin, normally used as a tracer for several environmental processes; such as soil redistribution, sediment source discrimination, atmospheric mass transport, and trace metal scavenging from the atmosphere. In this research the content of 7Be in soil, its seasonal variation throughout the year and its relationship with the rainfall regime in the Mato Frio creek micro-watershed was investigated, to assess its potential use in estimating soil erosion. The 7Be content in soil shows a marked variation throughout the year. Minimum 7Be values were observed in the dry season (from April to September) and were between 7 and 14 times higher in the rainy season (from October to March). The seasonal oscillations in 7Be soil content could be explained by the asymmetric rainfall regime. A highly linear relationship between rainfall amount and 7Be deposition was observed in rain water. A good agreement between 7Be soil content and 7Be atmospheric deposition was noticed, mainly in wet months. 7Be penetration in soil reaches a 5 cm depth, this could be explained by the soil type in the region. The soils are Acrisol type, characterized by low pH values and clay illuviation in deeper layers of the soil. In some regions of Brazil special attention should be paid if this radionuclide will be used as soil erosion tracer, taking into account the soil origin and its particular properties.
Assuntos
Berílio/análise , Monitoramento de Radiação , Radioisótopos/análise , Solo/química , Brasil , Chuva , Movimentos da ÁguaRESUMO
The Brazilian Instituto de Radioproteção e Dosimetria (IRD) runs a neutron individual monitoring system with a home-made TLD albedo dosemeter. It has already been characterised and calibrated in some reference fields. However, the complete energy response of this dosemeter is not known, and the calibration factors for all monitored workplace neutron fields are difficult to be obtained experimentally. Therefore, to overcome such difficulties, Monte Carlo simulations have been used. This paper describes the simulation of the HP(10) neutron response of the IRD TLD albedo dosemeter using the MCNPX transport code, for energies from thermal to 20 MeV. The validation of the MCNPX modelling is done comparing the simulated results with the experimental measurements for ISO standard neutron fields of (241)Am-Be, (252)Cf, (241)Am-B and (252)Cf(D2O) and also for (241)Am-Be source moderated with paraffin and silicone. Bare (252)Cf are used for normalisation.
Assuntos
Doses de Radiação , Dosímetros de Radiação , Monitoramento de Radiação/instrumentação , Proteção Radiológica/instrumentação , Dosimetria Termoluminescente/métodos , Algoritmos , Amerício/análise , Berílio/análise , Boro/análise , Brasil , Calibragem , Califórnio/análise , Simulação por Computador , Humanos , Teste de Materiais , Método de Monte Carlo , Nêutrons , Exposição Ocupacional/análise , Parafina/química , Monitoramento de Radiação/métodos , Proteção Radiológica/métodos , Sensibilidade e Especificidade , Silício/química , SoftwareRESUMO
The radiometric composition of bulk deposition samples, collected monthly for one year, February 2010 until January 2011, at a site located in Cienfuegos (22° 03' N, 80° 29' W) (Cuba), are analysed in this paper. Measurement of (7)Be and (210)Pb activity concentrations were carried out in 12 bulk deposition samples. The atmospheric deposition fluxes of (7)Be and (210)Pb are in the range of 13.2-132 and 1.24-8.29 Bq m(-2), and their mean values are: 56.6 and 3.97 Bq m(-2), respectively. The time variations of the different radionuclide have been discussed in relation with meteorological factors and the mean values have been compared to those published in recent literature from other sites located at different latitudes. The annual average flux of (210)Pb and (7)Be were 47 and 700 Bq m(-2) y(-1), respectively. Observed seasonal variations of deposition data are explained in terms of different environmental features. The atmospheric deposition fluxes of (7)Be and (210)Pb were moderately well correlated with precipitation and well correlated with one another. The (210)Pb/(7)Be ratios in the monthly depositions samples varied in the range of 0.05-0.10 and showed a strong correlation with the number of rainy days.
Assuntos
Poluentes Radioativos do Ar/análise , Berílio/análise , Radioisótopos de Chumbo/análise , Monitoramento de Radiação , Radioisótopos/análise , Cuba , Tempo (Meteorologia)RESUMO
The Younger Dryas stadial, a cold event spanning 12,800 to 11,500 years ago, during the last deglaciation, is thought to coincide with the last major glacial re-advance in the tropical Andes. This interpretation relies mainly on cosmic-ray exposure dating of glacial deposits. Recent studies, however, have established new production rates for cosmogenic (10)Be and (3)He, which make it necessary to update all chronologies in this region and revise our understanding of cryospheric responses to climate variability. Here we present a new (10)Be moraine chronology in Colombia showing that glaciers in the northern tropical Andes expanded to a larger extent during the Antarctic cold reversal (14,500 to 12,900 years ago) than during the Younger Dryas. On the basis of a homogenized chronology of all (10)Be and (3)He moraine ages across the tropical Andes, we show that this behaviour was common to the northern and southern tropical Andes. Transient simulations with a coupled global climate model suggest that the common glacier behaviour was the result of Atlantic meridional overturning circulation variability superimposed on a deglacial increase in the atmospheric carbon dioxide concentration. During the Antarctic cold reversal, glaciers advanced primarily in response to cold sea surface temperatures over much of the Southern Hemisphere. During the Younger Dryas, however, northern tropical Andes glaciers retreated owing to abrupt regional warming in response to reduced precipitation and land-surface feedbacks triggered by a weakened Atlantic meridional overturning circulation. Conversely, glacier retreat during the Younger Dryas in the southern tropical Andes occurred as a result of progressive warming, probably influenced by an increase in atmospheric carbon dioxide. Considered with evidence from mid-latitude Andean glaciers, our results argue for a common glacier response to cold conditions in the Antarctic cold reversal exceeding that of the Younger Dryas.