FCT: DF - Artigos em revista internacional com arbitragem científica
URI permanente para esta coleção:
Navegar
Entradas recentes
- Databases of L-shell X-ray intensity ratios for various elements after photon excitationPublication . Zidi, A.; Kahoul, A.; Marques, J. P.; Daoudi, S.; Sampaio, J. M.; Parente, F.; Hamidani, A.; Croft, S.; Favalli, A.; Kasri, Y.; Amari, K.; Berkani, B.; LIBPhys-UNL; DF – Departamento de Física; Elsevier Science B.V., Amsterdam.In this study, a comprehensive dataset of X-ray emission intensity ratios has been compiled, including ILβ/ILα, ILγ/ILα, ILl/ILα, ILγ/ILβ, ILl/ILγ, ILl/ILβ, ILγ5/ILα, ILγ44′/ILα, ILη/ILα, and ILγ1/ILα, extracted from literature spanning the years 1971 to 2023, and encompassing 83 research papers. Over this timeframe, a total of 2600 values were collected, comprising some 678 values for ILβ/ILα, 696 values for ILγ/ILα, 617 values for ILl/ILα, along with 132, 132, 89, 60, 70, 71, and 55 data points for ILγ/ILβ,ILl/ILγ, ILl/ILβ, ILγ5/ILα, ILγ44′/ILα, ILη/ILα, and ILγ1/ILα, respectively. The reported values are presented with precision up to three to four decimal places, accompanied by their associated uncertainties. Additionally, the tables include calculated weighted averages (ILi/ILj)W, uncertainty values (εISD, εESD), combined standard deviations (zISD, zESD), and average z-scores (z¯ISD,z¯ESD) for these intensity ratios. The data encompasses elements ranging from 39Y to 94Pu when excited by photon bombardment. The assessment of how these experimental data values are distributed according to atomic number indicates extensive coverage across most elements. However, a few isolated instances were identified where either no data or fewer than two data values were available.
- The role of coatings on the sealing of cork stoppersPublication . Fonseca, Ana P.; Adame, Carolina F.; Teodoro, Orlando M. N. D.; CeFITec – Centro de Física e Investigação Tecnológica; DF – Departamento de Física; Elsevier Science B.V., Amsterdam.Natural cork stoppers, renowned for their sealing efficacy in wine bottles, face challenges in gas-tightness due to cork surface irregularities. This study investigates the impact of lubricant coatings (silicone or paraffin emulsions), on cork stopper gas-tightness. These coatings facilitate cork conformity to glass, minimizing gaps at the interface and significantly improving sealing capacity. A small amount of lubricant leads to a two-order-of-magnitude reduction in gas flow. However, careful control of coating is crucial to ensure reliable sealing. Additionally, water absorption by cork is proposed to contribute to sealing by generating expansion forces and softening the cork, enhancing conformity to glass. This study emphasizes that natural cork stoppers should be viewed as both sealants and membranes. These findings shed light on the importance of surface treatments and water interaction in achieving reliable sealing in cork stoppers, ultimately ensuring the preservation and quality of bottled wine.
- Ring‐selective fragmentation in the tirapazamine molecule upon low‐energy electron attachmentPublication . Arthur‐Baidoo, Eugene; Ameixa, João; Ončák, Milan; Denifl, Stephan; CeFITec – Centro de Física e Investigação Tecnológica; DF – Departamento de Física; MDPI - Multidisciplinary Digital Publishing InstituteWe investigate dissociative electron attachment to tirapazamine through a crossed elec-tron–molecule beam experiment and quantum chemical calculations. After the electron is attached and the resulting anion reaches the first excited state, D1, we suggest a fast transition into the ground electronic state through a conical intersection with a distorted triazine ring that almost coincides with the minimum in the D1 state. Through analysis of all observed dissociative pathways produc-ing heavier ions (90–161 u), we consider the predissociation of an OH radical with possible roaming mechanism, as introduced in our recent letter [Angew Chem Int. Ed., 59, 17177 (2020)], to be the common first step. This destabilizes the triazine ring and leads to dissociation of highly stable nitrogen-containing species. The benzene ring is not altered during the process. Dissociation of small anionic fragments (NO2−, CN2−, CN−, NH2−, O−) cannot be conclusively linked to the OH predissociation mechanism; however, they again do not require dissociation of the benzene ring.
- Survival of polycyclic aromatic hydrocarbon knockout fragments in the interstellar mediumPublication . Gatchell, Michael; Ameixa, João; Ji, Ming Chao; Stockett, Mark H.; Simonsson, Ansgar; Denifl, Stephan; Cederquist, Henrik; Schmidt, Henning T.; Zettergren, Henning; DF – Departamento de Física; CeFITec – Centro de Física e Investigação Tecnológica; Nature PortfolioLaboratory studies play a crucial role in understanding the chemical nature of the interstellar medium (ISM), but the disconnect between experimental timescales and the timescales of reactions in space can make a direct comparison between observations, laboratory, and model results difficult. Here we study the survival of reactive fragments of the polycyclic aromatic hydrocarbon (PAH) coronene, where individual C atoms have been knocked out of the molecules in hard collisions with He atoms at stellar wind and supernova shockwave velocities. Ionic fragments are stored in the DESIREE cryogenic ion-beam storage ring where we investigate their decay for up to one second. After 10 ms the initially hot stored ions have cooled enough so that spontaneous dissociation no longer takes place at a measurable rate; a majority of the fragments remain intact and will continue to do so indefinitely in isolation. Our findings show that defective PAHs formed in energetic collisions with heavy particles may survive at thermal equilibrium in the interstellar medium indefinitely, and could play an important role in the chemistry in there, due to their increased reactivity compared to intact or photo-fragmented PAHs.
- Suitability of Short- and Long-Term Storage of Volatile Organic Compounds Samples in Syringe-Based ContainersPublication . Santos, Paulo Henrique Costa; Moura, Pedro Catalão; Vassilenko, Valentina; DF – Departamento de Física; LIBPhys-UNL; MDPI - Multidisciplinary Digital Publishing InstituteThe employment of advanced analytical techniques and instrumentation enables the tracing of volatile organic compounds (VOCs) in vestigial concentrations (ppbv-pptv range) for several emerging applications, such as the research of disease biomarkers in exhaled air, the detection of metabolites in several biological processes, and the detection of pollutants for air quality control. In this scope, the storage of gaseous samples is crucial for preserving the integrity and stability of the collected set of analytes. This study aims to assess the suitability of three commercially available syringes as air containers (AC) that are commonly used for the collection, storage, isolation, and transportation of samples: glass syringes with glass plungers (AC1), and two plastic syringes, one with plastic plungers (AC2), and one with rubbered plungers (AC3). For this purpose, 99 air samples with different times of storage (from 10 min to 24 h) were analyzed using a Gas Chromatography—Ion Mobility Spectrometry device and the degradation of the samples was properly assessed by comparing the changes in the VOCs’ emission profiles. The quality of the method was assured by via the measurement of the blank’s spectra before each experimental run, as well as by the consecutive measurement of the three replicates for each sample. A statistical analysis of the changes in the VOCs’ emission patterns was performed using principal component analysis (PCA). The results, with a total explained variance of 93.61%, indicate that AC3 is the most suitable option for the long-term storage of air samples. Thus, AC3 containers demonstrated a higher capacity to preserve the stability and integrity of the analytes compared to AC1 and AC2. The findings of the short-term effects analysis, up to 1 h, confirm the suitability of all analyzed syringe-based containers for sample-transferring purposes in onsite analysis.
- In Situ Indoor Air Volatile Organic Compounds Assessment in a Car Factory Painting LinePublication . Moura, Pedro Catalão; Santos, Fausto; Fujão, Carlos; Vassilenko, Valentina; DF – Departamento de Física; LIBPhys-UNL; MDPI - Multidisciplinary Digital Publishing InstituteProper working conditions must be one of the employers’ main concerns in any type of company but particularly in work locations where the employees are chronically exposed to hazardous compounds, like factories and production lines. Regarding this challenge, the present research addresses the mapping of a car factory painting line to possibly toxic volatile organic compounds emitted by all the coatings and chemicals used during the work shifts for the future evaluation of employees’ exposure. For the first time, a Gas Chromatography–Ion Mobility Spectrometry device was employed for the in situ detection of volatile organic compounds in an automotive factory. A total of 26 analytes were detected at nine different locations, of which 15 VOCs were accurately identified. Pure chemical-grade substances were used for the development of the VOC database. Although quantitative analysis was not the goal of this study, a calibration model was presented to one analyte for exemplificative purposes. Relative intensity profiles were plotted for all locations, revealing that some indoor VOCs can reach intensity levels up to 60 times higher than in outdoor air samples. The achieved results proved that the painting line has an abundant number of VOCs emitted from different sources and may lead to serious health risks for the employees. Additional studies shall be developed in the painting line for quantitative evaluation of the existing VOCs and their influence on the employees’ health conditions.
- The Role of Hydrogen Incorporation into Amorphous Carbon Films in the Change of the Secondary Electron YieldPublication . Bundaleski, Nenad; Adame, Carolina F.; Alves, Eduardo; Barradas, Nuno P.; Cerqueira, Maria F.; Deuermeier, Jonas; Delaup, Yorick; Ferraria, Ana M.; Ferreira, Isabel M. M.; Neupert, Holger; Himmerlich, Marcel; Rego, Ana Maria M. B. do; Rimoldi, Martino; Teodoro, Orlando M. N. D.; Vasilevskiy, Mikhail; Costa Pinto, Pedro; DF – Departamento de Física; CeFITec – Centro de Física e Investigação Tecnológica; DCM - Departamento de Ciência dos Materiais; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); MDPI - Multidisciplinary Digital Publishing InstituteOver the last few years, there has been increasing interest in the use of amorphous carbon thin films with low secondary electron yield (SEY) to mitigate electron multipacting in particle accelerators and RF devices. Previous works found that the SEY increases with the amount of incorporated hydrogen and correlates with the Tauc gap. In this work, we analyse films produced by magnetron sputtering with different contents of hydrogen and deuterium incorporated via the target poisoning and sputtering of CxDy molecules. XPS was implemented to estimate the phase composition of the films. The maximal SEY was found to decrease linearly with the fraction of the graphitic phase in the films. These results are supported by Raman scattering and UPS measurements. The graphitic phase decreases almost linearly for hydrogen and deuterium concentrations between 12% and 46% (at.), but abruptly decreases when the concentration reaches 53%. This vanishing of the graphitic phase is accompanied by a strong increase of SEY and the Tauc gap. These results suggest that the SEY is not dictated directly by the concentration of H/D, but by the fraction of the graphitic phase in the film. The results are supported by an original model used to calculate the SEY of films consisting of a mixture of graphitic and polymeric phases.
- Electron Scattering from 1-Methyl-5-NitroimidazolePublication . Lozano, Ana I.; Álvarez, Lidia; García-Abenza, Adrián; Guerra, Carlos; Kossoski, Fábris; Rosado, Jaime; Blanco, Francisco; Oller, Juan Carlos; Hasan, Mahmudul; Centurion, Martin; Weber, Thorsten; Slaughter, Daniel S.; Mootheril, Deepthy M.; Dorn, Alexander; Kumar, Sarvesh; Limão-Vieira, Paulo; Colmenares, Rafael; García, Gustavo; DF – Departamento de Física; CeFITec – Centro de Física e Investigação Tecnológica; MDPI - Multidisciplinary Digital Publishing InstituteIn this study, we present a complete set of electron scattering cross-sections from 1-Methyl-5-Nitroimidazole (1M5NI) molecules for impact energies ranging from 0.1 to 1000 eV. This information is relevant to evaluate the potential role of 1M5NI as a molecular radiosensitizers. The total electron scattering cross-sections (TCS) that we previously measured with a magnetically confined electron transmission apparatus were considered as the reference values for the present analysis. Elastic scattering cross-sections were calculated by means of two different schemes: The Schwinger multichannel (SMC) method for the lower energies (below 15 eV) and the independent atom model-based screening-corrected additivity rule with interferences (IAM-SCARI) for higher energies (above 15 eV). The latter was also applied to calculate the total ionization cross-sections, which were complemented with experimental values of the induced cationic fragmentation by electron impact. Double differential ionization cross-sections were measured with a reaction microscope multi-particle coincidence spectrometer. Using a momentum imaging spectrometer, direct measurements of the anion fragment yields and kinetic energies by the dissociative electron attachment are also presented. Cross-sections for the other inelastic channels were derived with a self-consistent procedure by sampling their values at a given energy to ensure that the sum of the cross-sections of all the scattering processes available at that energy coincides with the corresponding TCS. This cross-section data set is ready to be used for modelling electron-induced radiation damage at the molecular level to biologically relevant media containing 1M5NI as a potential radiosensitizer. Nonetheless, a proper evaluation of its radiosensitizing effects would require further radiobiological experiments.
- Thermal Desorption of 2,4,6-Trichloroanisole from CorkPublication . Monteiro, Susana; Bundaleski, Nenad; Lopes, Paulo; Cabral, Miguel; Teodoro, Orlando M. N. D.; DF – Departamento de Física; CeFITec – Centro de Física e Investigação Tecnológica; MDPI - Multidisciplinary Digital Publishing InstituteWhile extensive efforts have been made over the past two decades to understand how cork becomes contaminated by 2,4,6-trichloroanisole (TCA), the nature of its bond to cork remains unclear. A deeper understanding of this interaction is crucial in designing processes to effectively remove TCA from cork stoppers. This study presents an investigation into the thermal desorption of TCA from cork under vacuum conditions. To facilitate detection by a quadrupole mass spectrometer, samples were artificially contaminated with sufficient TCA. A calibration system was developed to determine the absolute rate of TCA released from the cork. Desorption spectra revealed two peaks at 80 °C and 170 °C. Despite the known variability of cork, repeated measurements demonstrated reasonable repeatability. The low-temperature peak decreased with time and after preheating the sample to 50 °C. It is proposed that the high-temperature peak corresponds to TCA bonded to the cork material. Experiments with naturally contaminated cork stoppers revealed a significant reduction in the amount of releasable TCA following a vacuum-heating process. This study provides an insightful discussion on the adsorption of TCA on cork and proposes an estimate for the adsorption energy. Furthermore, it discloses a process capable of removing TCA from natural cork stoppers.
- Amorphous carbon thin filmsPublication . Adame, C. F.; Alves, E.; Barradas, N. P.; Costa Pinto, P.; Delaup, Y.; Ferreira, I. M. M.; Neupert, H.; Himmerlich, M.; Pfeiffer, S.; Rimoldi, M.; Taborelli, M.; Teodoro, O. M. N. D.; Bundaleski, N.; DF – Departamento de Física; CeFITec – Centro de Física e Investigação Tecnológica; DCM - Departamento de Ciência dos Materiais; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); American Vacuum SocietyAmorphous carbon (a-C) films, having low secondary electron yield (SEY), are used at CERN to suppress electron multipacting in the beam pipes of particle accelerators. It was already demonstrated that hydrogen impurities increase the SEY of a-C films. In this work, a systematic characterization of a set of a-C coatings, deliberately contaminated by deuterium during the magnetron sputtering deposition, by scanning electron microscopy, ion beam analysis, secondary ion mass spectrometry, and optical absorption spectroscopy was performed to establish a correlation between the hydrogen content and the secondary electron emission properties. In parallel, the mechanisms of contamination were also investigated. Adding deuterium allows resolving the contributions of intentional and natural contamination. The results enabled us to quantify the relative deuterium/hydrogen (D/H) amounts and relate them with the maximum SEY (SEYmax). The first step of incorporation appears to be formation of D/H atoms in the discharge. An increase in both the flux of deposited carbon atoms and the discharge current with a D2 fraction in the gas discharge can be explained by target poisoning with deuterium species followed by etching of CxDy clusters, mainly by physical sputtering. For overall relative D/H amounts between 11% and 47% in the discharge gas, the SEYmax increases almost linearly from 0.99 to 1.38. An abrupt growth of SEYmax from 1.38 to 2.12 takes place in the narrow range of D/H relative content of 47%-54%, for which the nature of the deposited films changes to a polymer-like layer.