Calculated energy loss of swift light ions in platinum and gold: importance of the target electronic excitation spectrum

Understanding and predicting the energy loss of swift ions in metals is important for many applications of charged particle beams, such as analysis and modification of materials, and recently for modelling metal nanoparticle radiosensitisation in ion beam cancer therapy. We have calculated the stopping power of the transition metals Pt and Au for protons and alpha particles in a wide energy range, using the dielectric formalism, which realistically accounts for the excitation spectrum of each metal through the Mermin Energy Loss Function - Generalised Oscillator Strength methodology. For each combination of projectile, energy and target, we have considered: (i) the equilibrium charge state of the projectile through the target, (ii) the energy-loss due to electron capture and loss processes, and (iii) the energy loss resulting from the polarisation of the projectile's electronic cloud due to the self-induced electric field. Our calculated stopping powers show a fairly good agreement with the available experimental data for platinum and gold, particularly the most recent ones around the stopping power maximum, which validates the methodology we have used to be further extended to other transition metals. For the materials studied (platinum and gold), two commonly used and different sources of the experimental excitation spectrum yield comparable calculated stopping powers and mean excitation energies, the latter being closer to the most recent data provided in a recent ICRU Report than to previous compilations. Despite the small differences in the sources of excitation spectra of these metals, they lead to practically the same stopping power results as far as they reproduce the main excitation features of the material and fulfil physically motivated sum rules.Comment: 7 pages, 2 figure

Angular and Energy Distributions of Electrons Produced in Arbitrary Biomaterials by Proton Impact

We present a simple method for obtaining reliable angular and energy distributions of electrons ejected from arbitrary condensed biomaterials by proton impact. Relying on a suitable description of the electronic excitation spectrum and a physically motivated relation between the ion and electron scattering angles, it yields cross sections in rather good agreement with experimental data in a broad range of ejection angles and energies, by only using as input the target composition and density. The versatility and simplicity of the method, which can be also extended to other charged particles, make it especially suited for obtaining ionization data for any complex biomaterial present in realistic cellular environments.The authors recognize the financial support from the Spanish Ministerio de Economía y Competitividad and the European Regional Development Fund (Project No. FIS2010–17225). PdV acknowledges financial support from the European Union’s FP7-People Program (Marie Curie Actions) within the Initial Training Network No. 608163 "ARGENT". Support from the European COST Action MP1002 NanoIBCT is gratefully acknowledged

Opportunities for automation in beer processing

PòsterJun

Calculated energy loss of swift light ions in platinum and gold: importance of the target electronic excitation spectrum

Understanding and predicting the energy loss of swift ions in metals is important for many applications of charged particle beams, such as analysis and modification of materials, and recently for modelling metal nanoparticle radiosensitisation in ion beam cancer therapy. We have calculated the stopping power of the transition metals Pt and Au for protons and alpha particles in a wide energy range, using the dielectric formalism, which realistically accounts for the excitation spectrum of each metal through the Mermin Energy Loss Function - Generalised Oscillator Strength methodology. For each combination of projectile, energy and target, we have considered: (i) the equilibrium charge state of the projectile through the target, (ii) the energy-loss due to electron capture and loss processes, and (iii) the energy loss resulting from the polarisation of the projectile's electronic cloud due to the self-induced electric field. Our calculated stopping powers show a fairly good agreement with the available experimental data for platinum and gold, particularly the most recent ones around the stopping power maximum, which validates the methodology we have used to be further extended to other transition metals. For the materials studied (platinum and gold), two commonly used and different sources of the experimental excitation spectrum yield comparable calculated stopping powers and mean excitation energies, the latter being closer to the most recent data provided in a recent ICRU Report than to previous compilations. Despite the small differences in the sources of excitation spectra of these metals, they lead to practically the same stopping power results as far as they reproduce the main excitation features of the material and fulfil physically motivated sum rules.We thank financial support from the European Union's Horizon 2020 Research and Innovation programme under the Marie Sklodowska-Curie grant agreement no. 840752, the Spanish Ministerio de Economía y Competitividad and the European Regional Development Fund (Project no. PGC2018-096788-B-I00), and the Fundación Séneca (Project no. 19907/GERM/15)

Excitation and ionisation cross-sections in condensed-phase biomaterials by electrons down to very low energy: application to liquid water and genetic building blocks

Electronic excitations and ionisations produced by electron impact are key processes in the radiation-induced damage mechanisms in materials of biological relevance, underlying important medical and technological applications, including radiotherapy, radiation protection in manned space missions and nanodevice fabrication techniques. However, experimentally measuring all the necessary electronic interaction cross-sections for every relevant material is an arduous task, so it is necessary having predictive models, sufficiently accurate yet easily implementable. In this work we present a model, based on the dielectric formalism, to provide reliable ionisation and excitation cross-sections for electron-impact on complex biomolecular media, considering their condensed-phase nature. We account for the indistinguishability and exchange between the primary beam and excited electrons, for the molecular electronic structure effects in the electron binding, as well as for low-energy corrections to the first Born approximation. The resulting approach yields total ionisation cross-sections, energy distributions of secondary electrons, and total electronic excitation cross-sections for condensed-phase biomaterials, once the electronic excitation spectrum is known, either from experiments or from a predictive model. The results of this methodology are compared with the available experimental data in water and DNA/RNA molecular building blocks, showing a very good agreement and a great predictive power in a wide range of electron incident energies, from the large values characteristic of electron beams down to excitation threshold. The proposed model constitutes a very useful procedure for computing the electronic interaction cross-sections for arbitrary biological materials in a wide range of electron incident energies.This work has received funding from the European Union's Horizon 2020 Research and Innovation programme under the Marie Sklodowska-Curie grant agreement no. 840752, from the Spanish Ministerio de Economía y Competitividad and the European Regional Development Fund (Project no. PGC2018-096788-B-I00), from the Fundación Séneca (Project no. 19907/GERM/15) and from the Conselleria d'Educació, Investigació, Cultura i Esport de la Generalitat Valenciana (Project no. AICO/2019/070). PdV acknowledges further financial support provided by the Spanish Ministerio de Economía y Competitividad by means of a Juan de la Cierva postdoctoral fellowship (FJCI-2017-32233)

Simulation of the energy spectra of swift light ion beams after traversing cylindrical targets: a consistent interpretation of experimental data relevant for hadron therapy

We have performed detailed simulations of the energy spectra, recorded at several angles, of proton and helium ion beams after traversing thin cylindrical targets of different nature (liquid water and ethanol jets, as well as a solid aluminium wire), in order to reproduce a series of measurements intended to assess the stopping power of 0.3–2 MeV ions. The authors of these experiments derived values of the stopping power of liquid water (a quantity essential for the evaluation of radiation effects in materials, particularly for radiotherapy purposes) that are ~10% lower than what is expected from other measurements and theories. In our simulations, instead of treating the stopping power as an unknown free parameter to be determined, we use as input the electronic stopping power accurately calculated within the dielectric formalism. We take into account in the simulations the different interactions that each projectile can experience when moving through the target, such as electronic stopping, nuclear scattering or electron charge-exchange processes. The detailed geometry of the target is also accounted for. We find that our simulated energy distributions are in excellent agreement with the published measurements when the diameter of the cylindrical targets is slightly reduced, what is compatible with the potential evaporation of the liquid jets. On the basis of such an excellent agreement, we validate the accuracy of the model we use to calculate electronic excitation cross sections for ions in condensed matter in its range of applicability (particularly the electronic stopping power) needed for charged particle transport models, and we offer a consistent, but alternative, interpretation for these experiments on ion irradiation of cylindrical targets.Financial support was provided by the Spanish Ministerio de Economía y Competitividad, the Spanish Ministerio de Ciencia, Innovación y Universidades and the European Regional Development Fund (Projects No. FIS2014-58849-P and PGC2018-096788-B-I00), as well as by the Fundación Séneca - Agencia de Ciencia y Tecnología de la Región de Murcia (Project No. 19907/GERM/15). PdV also acknowledges financial support provided by the Alexander von Humboldt Stiftung/Foundation through a postdoctoral fellowship

Elements of a gravitational lens system assuming an elliptical galaxy model

This work studies some elements of gravitational lensing by galaxies such as the lens equation, deflection angle, lensing potential and time delay, modeling the mass distribution of the lensing galaxy as an elliptical galaxy. The mass distribution function ρ of the deflecting galaxy indicates that it has a nucleus with radius a in its core, a free-form parameter b (b > a), and that the mass density of the nucleus is ρ0. The mass density distribution ρ allows us to find the surface mass density Σ (projected on the plane of the lens), followed by general elements of the gravitational lens expressed in terms of the geometric parameters a and b. The relation between these parameters is defined by the adimensional factor n = b/a > 1. The results of this work can be applied to any galactic lens system to conduct an analysis based on the temporal delay between two images and to determine the conditions that must be satisfied by the parameter n

Promoción de la conciencia de los estudiantes de pregrado sobre la importancia de pensar críticamente acerca de la información científica falsa o inexacta presentada en artículos de prensa

Being aware of the importance of thinking critically about wrong scientific information presented in news articles is an important form of scientific media literacy. However, little is known about how undergraduates evaluate wrong scientific information presented in news articles. This article discusses the effect of a teaching–learning sequence (TLS) in promoting students’ awareness of the importance of thinking critically about false or inaccurate scientific information presented in news articles. It examines the written and oral arguments produced by 141 university students (73 females and 68 males, 16–22 years old) in Colombia during a complete TLS supervised by the same instructor. The data used in this analysis was collected from students’ written responses, and audio and video recordings. The first aim of this investigation was to provide evidence of how undergraduates evaluate wrong scientific information presented in news articles when purposely no definition of misleading information is given. The second was to assess the effectiveness of the TLS in promoting students’ awareness of the importance of thinking critically about wrong scientific information presented in news articles. The findings show that not all participants perceived misleading information in the same way, and students usually over-estimate the truth or certainty that can be attributed to scientific information communicated in news articles.Un aspecto de la alfabetización mediática en ciencias tiene que ver con ser consciente de la importancia de pensar críticamente acerca de la información científica errónea presentada en artículos de prensa. Empero, poco se conoce sobre cómo los estudiantes de pregrado evalúan este tipo de información. En este artículo se discute el efecto de una secuencia de enseñanza-aprendizaje (TLS, por sus siglas en inglés) a la hora de concientizar a los estudiantes sobre la importancia de pensar críticamente acerca de información científica falsa o inexacta presentada en artículos de prensa. El artículo examina los argumentos escritos y orales de 141 estudiantes universitarios (73 mujeres y 68 hombres, entre 16 y 22 años de edad) en Colombia, durante una TLS supervisada por el mismo profesor. Los datos empleados para este análisis fueron tomados de las respuestas escritas de los estudiantes y registros de audio y video. El primer objetivo de esta investigación fue proveer evidencia de cómo estudiantes de pregrado evalúan información científica errónea presentada en artículos de prensa cuando no se les brinda deliberadamente una definición de información engañosa. El segundo objetivo fue evaluar la efectividad de la TLS al momento de concientizar a los estudiantes sobre la importancia de pensar críticamente acerca de información científica errónea presentada en artículos de prensa. Los resultados muestran que no todos los participantes percibieron la información engañosa del mismo modo. También se encontró que los estudiantes usualmente sobrestiman la verdad o la certeza que se puede atribuir a la información científica comunicada en artículos de prensa

Vitamin D, a modulator of musculoskeletal health in chronic kidney disease

The spectrum of activity of vitamin D goes beyond calcium and bone homeostasis, and growing evidence suggests that vitamin D contributes to maintain musculoskeletal health in healthy subjects as well as in patients with chronic kidney disease (CKD), who display the combination of bone metabolism disorder, muscle wasting, and weakness. Here, we review how vitamin D represents a pathway in which bone and muscle may interact. In vitro studies have confirmed that the vitamin D receptor is present on muscle, describing the mechanisms whereby vitamin D directly affects skeletal muscle. These include genomic and non-genomic (rapid) effects, regulating cellular differentiation and proliferation. Observational studies have shown that circulating 25-hydroxyvitamin D levels correlate with the clinical symptoms and muscle morphological changes observed in CKD patients. Vitamin D deficiency has been linked to low bone formation rate and bone mineral density, with an increased risk of skeletal fractures. The impact of low vitamin D status on skeletal muscle may also affect muscle metabolic pathways, including its sensitivity to insulin. Although some interventional studies have shown that vitamin D may improve physical performance and protect against the development of histological and radiological signs of hyperparathyroidism, evidence is still insufficient to draw definitive conclusions