Quantification of soil erosion using 7Be in a steep watershed used for natural grazing in Brazil.

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.

Theoretical study of boron, beryllium and lithium clusters (n=2-6), adsorption on graphitic carbon nitride and the study of acceptor-donor orbital of the coordination of a styrene molecule on [cluster/g-C3N4] systems.

The adsorption of boron, beryllium and lithium clusters on graphitic carbon nitride g-C3N4, and the adsorption of styrene molecule on the B, Be, Li cluster/g-C3N4 sheet have been investigated through the density functional theory (DFT) calculations. Our calculations show distortion of the geometry of the clusters when coordinating with the g-C3N4 sheet. Boron (n = 5 and 6), beryllium (n = 2-4, 6) and Li3 cluster on g-C3N4 present characteristics to adsorb a styrene molecule. The styrene on Be4/g-C3N4 system exhibits better adsorption, due to the beryllium atoms have strong interactions with the π-orbitals of the aromatic ring of the styrene molecule. The study of natural bond orbitals of styrene-cluster/g-C3N4 systems showed the donation process from the styrene molecule and the g-C3N4 sheet towards the boron, beryllium and lithium clusters. Only back donation was observed the boron and beryllium clusters.

Assessment of runoff using 7Be in vineyards in the central valley of Chile.

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 24 kg 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.

A kinetic comparison between E2P and the E2P-like state induced by a beryllium fluoride complex in the Na,K-ATPase. Interactions with Rb.

Metal-fluoride complexes have been used to induce E2P-like states with the aim of studying the events that occur during E2P hydrolysis in P-type ATPases. In the present work, we compared the E2P-like state induced by a beryllium fluoride complex (BeFx) with the actual E2P state formed through backdoor phosphorylation of the Na,K-ATPase. Formation of E2P and E2P-like states were investigated employing the styryl dye RH421. We found that BeFx is the only fluorinated phosphate analog that, like Pi, increases the RH421 fluorescence. The observed rate constant, kobs, for the formation of E2P decreases with [Pi] whereas that of E2BeFx increases with [BeFx]. This might wrongly be taken as evidence of a mechanism where the binding of BeFx induces a conformational transition. Here, we rather propose that, like for Pi, binding of BeFx follows a conformational-selection mechanism, i.e. it binds to the E2 conformer forming a complex that is much more stable than E2P, as seen from its impaired capacity to return to E1 upon addition of Na+. Although E2P and E2BeFx are able to form states with 2 occluded Rb+, both enzyme complexes differ in that the affinity for the binding and occlusion of the second Rb+ is much lower in E2BeFx than in E2P. The higher rates of Rb+ occlusion and deocclusion observed for E2BeFx, as compared to those observed for other E2P-like transition and product states suggest a more open access to the cation transport sites, supporting the idea that E2BeFx mimics the E2P ground state.

EXPERIMENTAL AND COMPUTATIONAL EVALUATION OF EFFECTIVE CENTRE FROM A LONG COUNTER AT NEUTRON METROLOGY LABORATORY IN BRAZIL.

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.

ALGORITHM BASED ON ARTIFICIAL BEE COLONY FOR UNFOLDING OF NEUTRON SPECTRA OBTAINED WITH BONNER SPHERES.

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.

IRRADIATOR SYSTEM FOR MANGANESE SULFATE BATH EFFICIENCY MEASUREMENTS USING A PLUTONIUM-BERYLLIUM NEUTRON SOURCE.

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.

IMPROVEMENTS IN THE THERMAL NEUTRON CALIBRATION UNIT, TNF2, AT LNMRI/IRD.

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.

COMPARISON OF THE NEUTRON ENERGY RESPONSE OF TWO DIFFERENT TLD ALBEDO DOSEMETERS.

Albedo dosemeters remain the most used dosemeters in neutron individual monitoring. In Brazil, most of the neutron occupational fields are from radionuclide sources, often without any moderation, where albedo dosemeters have poor energy response. The purpose of this work is to compare the HP(10) energy response of the IRD and ALNOR TLD albedo dosemeter systems, calculated by their modelling with Monte Carlo code MCNPX. Their energy responses are similar, as expected, but the IRD system is about five times more sensitive than the ALNOR one. IRD albedo system can measure the Brazilian monthly recording level of 0.2 mSv, even for bare 252Cf and 241Am-Be neutron fields. On the other hand, the ALNOR system can measure values higher than 0.2 mSv only after huge moderation of theses sources. These results show that IRD TLD albedo is more suitable than the ALNOR one to measure low doses at occupational fields from radionuclide sources.

Thermoluminescence of metallic oxides. Development and applications in Mexico: An overview.

Interest in the study of the thermoluminescence of metallic oxides doped with various elements has been steadily increasing due to the characteristics of these materials and their possible applications in the dosimetry of ionizing radiation. Metal oxides such as zirconium oxide (ZrO2), aluminum oxide Al2O3, titanium oxide (TiO2), hafnium oxide (HfO2) and beryllium oxide (BeO) are very interesting semiconductor materials having a wide band gap with different important applications. Since 1998, in our country we have developed these materials un-doped and doped with various elements, using different preparation methods. These materials have been obtained in powder form, thin films or in pellets made by mixing the TL powder with PTFE. Thermoluminescent and dosimetric characteristics of these materials have been studied and have been used successfully in various applications. It is presented an overview of the development of these materials in Mexico for the past 20 years.

Wet deposition and soil content of Beryllium - 7 in a micro-watershed of Minas Gerais (Brazil).

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.

Effect of casting atmosphere on the marginal deficiency and misfit of Ni-Cr alloys with and without beryllium.

STATEMENT OF PROBLEM: The marginal adaptation of prosthetic crowns is still a significant clinical problem. PURPOSE: The purpose of this in vitro study was to evaluate the marginal deficiency and misfit of Ni-Cr alloys with and without beryllium under different casting conditions. MATERIAL AND METHODS: Four casting conditions were selected: flame-torch, induction/argon, induction/vacuum, and induction/air; and 2 alloys were used, Ni-Cr-Be and Ni-Cr. For each group, 10 metal specimens were prepared. Silicone indirect impressions and analysis of the degree of rounding were used to evaluate the marginal deficiencies of metal copings, and a standardized device for the setting pressure associated with optical microscopy was used to analyze the marginal misfit. Results were evaluated with 2-way ANOVA (α=.05), followed by the Tukey honest significant difference post hoc test, and the Pearson correlation test (α=.05). RESULTS: Alloy (P<.001) and casting technique (P<.001) were shown to affect marginal deficiencies. The Ni-Cr cast using the torch technique showed the highest marginal deficiency, and the Ni-Cr-Be cast in a controlled argon atmosphere showed the lowest (P<.001). Alloy (P=.472) and casting techniques (P=.206) did not affect the marginal misfit, but significant differences were found in the interaction (P=.001); the lowest misfit was achieved using the Ni-Cr-Be, and the highest misfit occurred with the molten Ni-Cr, using the cast torch technique. No correlation was found between deficiency and marginal misfit (r=.04, P=.69). CONCLUSIONS: The interactions demonstrated that the alloy containing beryllium that was cast in an argon atmosphere led to reduced marginal deficiency. Improved marginal adaptation can be achieved for the same alloy by using the torch technique.

MCNP SIMULATION OF THE HP(10) ENERGY RESPONSE OF A BRAZILIAN TLD ALBEDO NEUTRON INDIVIDUAL DOSEMETER, FROM THERMAL TO 20 MeV.

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.

Atmospheric deposition patterns of (210)Pb and (7)Be in Cienfuegos, Cuba.

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.

A major advance of tropical Andean glaciers during the Antarctic cold reversal.

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.

Study of neutron scattering contribution on Hp(10) and H*(10) calibration in the Brazilian National Low Scattering Laboratory.

The neutron scattering at the Low Scattering Laboratory of the Brazilian National Neutron Laboratory has been studied using three different methods. The measurements have been done with a traceable standard (241)Am-Be from source-to-detector distances of 0.52-3.00 m. The obtained results with the variation distance methods are in agreement. Measurements with a large shadow cone are not worth for larger distances due to overshadowing. As the quantity required in a calibration is the response of the device being calibrated to the scattered neutron component in order to subtract this from the total response, for these purposes, the distance variation method must be used for each device. To quantify absolutely the scattering contribution on the quantity rates of fluence, Hp(10) and H*(10) in irradiation procedures, a Bonner sphere spectrometer with the shadow cone was employed. The evaluated scattering correction factor value may be employed for a distance of 1.00 m.

Neutron metrology laboratory facility simulation.

The Neutron Low Scattering Laboratory in Brazil has been completely rebuilt. Evaluation of air attenuation parameters and neutron component scattering in the room was done using Monte Carlo simulation code. Neutron fields produced by referenced neutron source were used to calculate neutron scattering and air attenuation.

Thermal neutron calibration channel at LNMRI/IRD.

The Brazilian Metrology Laboratory of Ionizing Radiations (LNMRI) standard thermal neutron flux facility was designed to provide uniform neutron fluence for calibration of small neutron detectors and individual dosemeters. This fluence is obtained by neutron moderation from four (241)Am-Be sources, each with 596 GBq, in a facility built with blocks of graphite/paraffin compound and high-purity carbon graphite. This study was carried out in two steps. In the first step, simulations using the MCNPX code on different geometric arrangements of moderator materials and neutron sources were performed. The quality of the resulting neutron fluence in terms of spectrum, cadmium ratio and gamma-neutron ratio was evaluated. In the second step, the system was assembled based on the results obtained on the simulations, and new measurements are being made. These measurements will validate the system, and other intercomparisons will ensure traceability to the International System of Units.

Annual variation of (7)Be soil inventory in a semiarid region of central Argentina.

Reliable information on environmental radionuclides atmospheric entrance, and their distribution along the soil profile, is a necessary condition for using these soil and sediment tracers to investigate key environmental processes. To address this need, (7)Be content in rainwater and the wet deposition in a semiarid region at San Luis Province, Argentina, were studied. Following these researches, in the same region, we have assessed the (7)Be content along a soil profile, during 2.5 years from September 2009 to January 2012. As expected, the specific activity values in soil samples in the wet period (November-April) were higher than in the dry period (May-October). During the investigated period (2009 - beginning 2012) and for all sampled points, the maximum value of the (7)Be specific activity (Bq kg(-1)) was measured at the surface level. A typical decreasing exponential function of (7)Be areal activity (Bq m(-2)) with soil mass depth (kg m(-2)) was found and the key distribution parameters were determined for each month. The minimum value of areal activity was 51 Bq m(-2) in August, and the maximum was 438 Bq m(-2) in February. The relaxation mass depth ranges from 2.9 kg m(-2) in March to 1.3 kg m(-2) in August. (7)Be wet deposition can explain in a very significant proportion the (7)Be inventory in soil. During the period of winds in the region (September and October), the (7)Be content in soil was greater than the expected contribution from wet deposition, situation that is compatible with a higher relative contribution of dry deposition at this period of the year.

Electronic properties of functionalized (5,5) beryllium oxide nanotubes.

Using the density functional theory (DFT) we study the structural and electronic properties of functionalized (5,5) chirality single wall beryllium oxide nanotubes (SW-BeONTs), i.e. armchair nanotubes. The nanotube surface and ends are functionalized by the hydroxyl (OH) functional group. Our calculations consider the Hamprecht-Cohen-Tozer-Handy functional in the generalized gradient approximation (HCTH-GGA) to deal with the exchange-correlation energies, and the base function with double polarization (DNP). The geometry optimization of both defects free and with point defects nanotubes is done applying the criterion of minimum energy. Six configurations are considered: The OH oriented toward the Be (on the surface and at the end), toward the O (on the surface and at the end) and placed at the nanotube ends. Simulation results show that the nanotube functionalization takes place at the nanotube ends with the BeO bond displaying hydrogen-like bridge bonds. Moreover the nanotube semiconductor behavior remains unchanged. The polarity is high (it shows a transition from covalent to ionic) favoring solvatation. On the other hand, the work function low value suggests this to be a good candidate for the device fabrication. When the nanotube contains surface point defects the work function is reduced which provides excellent possibilities for the use of this material in the electronic industry.