Systematic influences on the areas of peaks in gamma-ray spectra that have a large statistical uncertainty

A method is presented for calculating the expected number of counts in peaks that have a large relative peak-area uncertainty and appear in measured gamma-ray spectra. The method was applied to calculations of the correction factors for peaks occurring in the spectra of radon daughters. It was shown that the factors used for correcting the calculated peak areas to their expected values decrease with an increasing relative peak-area uncertainty. The accuracy of taking the systematic influence inducing the correction factors into account is given by the dispersion of the correction factors corresponding to specific peaks. It was shown that the highest accuracy is obtained in the peak analyses with the GammaVision and Gamma-W software.Postprint (author's final draft

Operando NAP-XPS studies of a ceria-supported Pd catalyst for CO oxidation

Supported Pd/CeO2 catalytic systems have been widely investigated in the low-temperature oxidation of CO (LTO CO) due to the unique oxygen storage capacity and redox properties of the ceria support, which highly influence the structural, chemical and electronic state of Pd species. Herein, operando near-ambient pressure XPS (NAP-XPS) technique has allowed the study of a conventional Pd/CeO2 catalyst surface during the CO oxidation reaction under experimental conditions closer to the actual catalytic reaction, unfeasible with other surface science techniques that demand UHV conditions. SEM, HRTEM and XRD analyses of the powder catalyst, prepared by conventional incipient wetness impregnation, reveal uniformly CeO2-loaded Pd NPs of less than 2 nm size, which generated an increase in oxygen vacancies with concomitant ceria reduction, as indicated by H2-TPR and Raman measurements. Adsorbed peroxide (O22-) species on the catalyst surface could also be detected by Raman spectra. Operando NAP-XPS results obtained at the ALBA Synchrotron Light Source revealed two kinds of Pd species under reaction conditions, namely PdOx and PdII ions in a PdxCe1-xO2-d solution, the latter one appearing to be crucial for the CO oxidation. By means of a non-destructive depth profile analysis using variable synchrotron excitation energies, the location and the role of these palladium species in the CO oxidation reaction could be clarified: PdOx was found to prevail on the upper surface layers of the metallic Pd supported NPs under CO, while under reaction mixture it was rapidly depleted from the surface, leaving a greater amount in the subsurface layers (7% vs. 12%, respectively). On the contrary, the PdxCe1-xO2-d phase, which was created at the Pd–CeO2 interface in contact with the gas environment, appeared to be predominant on the surface of the catalyst. Its presence was crucial for CO oxidation evolution, acting as a route through which active oxygen species could be transferred from ceria to Pd species for CO oxidation.Peer ReviewedPostprint (published version

Bimetallic NiFe nanoparticles supported on CeO2 as catalysts for methane steam reforming

Ni-Fe nanocatalysts supported on CeO2 have been prepared for the catalysis of methane steam reforming (MSR) aiming for coke-resistant noble metal-free catalysts. The catalysts have been synthesized by traditional incipient wetness impregnation as well as dry ball milling, a green and more sustainable preparation method. The impact of the synthesis method on the catalytic performance and the catalysts’ nanostructure has been investigated. The influence of Fe addition has been addressed as well. The reducibility and the electronic and crystalline structure of Ni and Ni-Fe mono- and bimetallic catalysts have been characterized by temperature programmed reduction (H2-TPR), in situ synchrotron X-ray diffraction (SXRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Their catalytic activity was tested between 700 and 950 °C at 108 L gcat-1 h-1 and with the reactant flow varying between 54 and 415 L gcat-1 h-1 at 700 °C. Hydrogen production rates of 67 mol gmet-1 h-1 have been achieved. The performance of the ball-milled Fe0.1Ni0.9/CeO2 catalyst was similar to that of Ni/CeO2 at high temperatures, but Raman spectroscopy revealed a higher amount of highly defective carbon on the surface of Ni-Fe nanocatalysts. The reorganization of the surface under MSR of the ball-milled NiFe/CeO2 has been monitored by in situ near-ambient pressure XPS experiments, where a strong reorganization of the Ni-Fe nanoparticles with segregation of Fe toward the surface has been observed. Despite the catalytic activity being lower in the low-temperature regime, Fe addition for the milled nanocatalyst increased the coke resistance and could be an efficient alternative to industrial Ni/Al2O3 catalysts.Peer ReviewedPostprint (published version

Investigation of the evolution of Pd-Pt supported on ceria for dry and wet methane oxidation

Efficiently treating methane emissions in transportation remains a challenge. Here, we investigate palladium and platinum mono- and bimetallic ceria-supported catalysts synthesized by mechanical milling and by traditional impregnation for methane total oxidation under dry and wet conditions, reproducing those present in the exhaust of natural gas vehicles. By applying a toolkit of in situ synchrotron techniques (X-ray diffraction, X-ray absorption and ambient pressure photoelectron spectroscopies), together with transmission electron microscopy, we show that the synthesis method greatly influences the interaction and structure at the nanoscale. Our results reveal that the components of milled catalysts have a higher ability to transform metallic Pd into Pd oxide species strongly interacting with the support, and achieve a modulated PdO/Pd ratio than traditionally-synthesized catalysts. We demonstrate that the unique structures attained by milling are key for the catalytic activity and correlate with higher methane conversion and longer stability in the wet feed.Peer ReviewedPostprint (published version

Izaña Atmospheric Research Center. Activity Report 2019-2020

Editors: Emilio Cuevas, Celia Milford and Oksana Tarasova.[EN]The Izaña Atmospheric Research Center (IARC), which is part of the State Meteorological Agency of Spain (AEMET), is a site of excellence in atmospheric science. It manages four observatories in Tenerife including the high altitude Izaña Atmospheric Observatory. The Izaña Atmospheric Observatory was inaugurated in 1916 and since that date has carried out uninterrupted meteorological and climatological observations, contributing towards a unique 100-year record in 2016. This reports are a summary of the many activities at the Izaña Atmospheric Research Center to the broader community. The combination of operational activities, research and development in state-of-the-art measurement techniques, calibration and validation and international cooperation encompass the vision of WMO to provide world leadership in expertise and international cooperation in weather, climate, hydrology and related environmental issues.[ES]El Centro de Investigación Atmosférica de Izaña (CIAI), que forma parte de la Agencia Estatal de Meteorología de España (AEMET), representa un centro de excelencia en ciencias atmosféricas. Gestiona cuatro observatorios en Tenerife, incluido el Observatorio de Izaña de gran altitud, inaugurado en 1916 y que desde entonces ha realizado observaciones meteorológicas y climatológicas ininterrumpidas y se ha convertido en una estación centenaria de la OMM. Estos informes resumen las múltiples actividades llevadas a cabo por el Centro de Investigación Atmosférica de Izaña. El liderazgo del Centro en materia de investigación y desarrollo con respecto a las técnicas de medición, calibración y validación de última generación, así como la cooperación internacional, le han otorgado una reputación sobresaliente en lo que se refiere al tiempo, el clima, la hidrología y otros temas ambientales afines

Experimental analysis of the mass eficiency curve for gross alphya activity and morphological study of the residue obtained by the co-precipitation method

Gross alpha activity determination in drinking water is one of the radiological parameters that must be determined in order to decide whether further specific analyses of radionuclides in samples is required. This parameter can be determined by the co-precipitation method using a ZnS(Ag) scintillation detector or a proportional counter. The method consists of collecting all alpha emitters of interest using barium and iron as carriers as they provide more uniform and homogeneous residues than the evaporation method, especially for highly saline waters. In the course of our work, the efficiencies of the gas proportional and ZnS(Ag) detectors for alpha particle detection in water residues were studied in function of sample mass (precipitate) with residues ranging between 16.0 and 35.0mg. In addition, the structure and morphological composition of a residue collected by the co-precipitation method was studied with the aim of verifying whether the residue is a homogeneous mixture. The effect of alpha energy on the efficiency and stability of the calibration samples (mass and efficiency) was studied using (230)Th, natural uranium ((nat)U) and (241)Am radionuclides.Postprint (published version

Natural and antropogenic radionuclides in airborne particulate samples collected in Barcelona (Spain)

Results for naturally occurring 7Be, 210Pb, 40K, 214Bi, 214Pb, 212Pb, 228Ac and 208Tl and anthropogenic 137Cs in airborne particulate matter in the Barcelona area during the period from January 2001 to December 2005 are presented and discussed. The 212Pb and 208Tl, 214Bi and 214Pb, 7Be and 210Pb radionuclide levels showed a significant correlation with each other, with correlation coefficients of 0.99, 0.78 and 0.69, respectively, suggesting similar origin/behaviour of these radionuclides in the air. Caessium-137 and Potassium-40 were transported to the air as resuspended particle from the soil. The 7Be and 210Pb concentrations showed similar seasonal variations, with a tendency for maximum concentrations during the summer months. An inverse relationship was observed between the 7Be, 210Pb, 40K and 137Cs concentrations and weekly rainfall, indicating washout of atmospheric aerosols carrying these radionuclides. 2008 Elsevier Ltd. All rights reserved.Postprint (published version

Experimental analysis of the mass eficiency curve for gross alphya activity and morphological study of the residue obtained by the co-precipitation method

Gross alpha activity determination in drinking water is one of the radiological parameters that must be determined in order to decide whether further specific analyses of radionuclides in samples is required. This parameter can be determined by the co-precipitation method using a ZnS(Ag) scintillation detector or a proportional counter. The method consists of collecting all alpha emitters of interest using barium and iron as carriers as they provide more uniform and homogeneous residues than the evaporation method, especially for highly saline waters. In the course of our work, the efficiencies of the gas proportional and ZnS(Ag) detectors for alpha particle detection in water residues were studied in function of sample mass (precipitate) with residues ranging between 16.0 and 35.0mg. In addition, the structure and morphological composition of a residue collected by the co-precipitation method was studied with the aim of verifying whether the residue is a homogeneous mixture. The effect of alpha energy on the efficiency and stability of the calibration samples (mass and efficiency) was studied using (230)Th, natural uranium ((nat)U) and (241)Am radionuclides

Natural and antropogenic radionuclides in airborne particulate samples collected in Barcelona (Spain)

Results for naturally occurring 7Be, 210Pb, 40K, 214Bi, 214Pb, 212Pb, 228Ac and 208Tl and anthropogenic 137Cs in airborne particulate matter in the Barcelona area during the period from January 2001 to December 2005 are presented and discussed. The 212Pb and 208Tl, 214Bi and 214Pb, 7Be and 210Pb radionuclide levels showed a significant correlation with each other, with correlation coefficients of 0.99, 0.78 and 0.69, respectively, suggesting similar origin/behaviour of these radionuclides in the air. Caessium-137 and Potassium-40 were transported to the air as resuspended particle from the soil. The 7Be and 210Pb concentrations showed similar seasonal variations, with a tendency for maximum concentrations during the summer months. An inverse relationship was observed between the 7Be, 210Pb, 40K and 137Cs concentrations and weekly rainfall, indicating washout of atmospheric aerosols carrying these radionuclides. 2008 Elsevier Ltd. All rights reserved

Natural and artificial radionuclides in sludge, sand, granular activated carbon and reverse osmosis brine from a metropolitan drinking water treatment plant

Postprint (author's final draft