Search

Molten salts as heat transfer fluids (HTF) for concentrated solar power (CSP) plant application are considered as the best thermal storage medium, and more precisely molten chlorides, presenting a wide operating range and coupled with competitive cost. Furthermore, MgCl2-NaCl-KCl (MgNaK) mixture appeared as the most promising one but need further studies to better understand its thermophysical properties. Indeed, its hydrated form leads to the formation of corrosive compounds. In this research, two different methods are used to model the ternary mixture. The dehydration process is evaluated by thermodynamical calculations with Thermocalc software. Then, the local structure, thermal conductivity and viscosity are estimated by means of molecular dynamics simulation, with LAMMPS package. The results were close to past simulations studies and experimental references, but discrepancies need to be further minimized regarding some variable fluctuations.

12 pags., 6 figs., 2 tabs., The mass spectrum of R-carvone measured at 70 eV electron impact energy, in the mass region of 1–151 amu, is reported in this work. We observed in this spectrum 103 peaks associated with ionic fragmentation, 55 of them with abundances greater than 1%. The relative abundances, from this study, compare reasonably well with the corresponding values reported in the literature where such a comparison can be made. The R-carvone Ionization Energy (IE), as well as the ionic energy formation thresholds (Appearance Energy - AE) were experimentally determined for the 35 most intense cations registered in the mass spectrum, which provided values for 38 AEs and Wannier exponents (p) and the IE of this molecule. The values of the AEs and Wannier exponents produced in this work, to the best of our knowledge, are being presented for the first time to the scientific community, except for the masses of 135 amu and 150 amu. We also suggest some ionic fragmentation mechanisms and molecular structural ionic fragmentation mechanisms for R-carvone, based on the AE and p values found in this work., This work was supported by the Brazilian Conselho Nacional de Desenvolvimento Científico e Tecnologico (CNPq), Fundaçao de Amparo a Pesquisa do Estado de Minas Gerais (FAPEMIG) and FINEP. M.C.A.L. acknowledges financial support from CNPq, while W.A.D.P., A.C.P.F. and R.A.A.A. acknowledge their fellowships from CAPES and FAPEMIG. Some financial assistance from the Australian Research Council through grant # DP180101655 is also noted. Finally, G. Garcia thanks the CSIC project LINKA20085

8 pags., 6 figs., 5 tabs., The correlation between the absorbed energy and the induced biological damage still has unclear aspects, especially in the low energy and low dose rate irradiation regimes. From the knowledge of the molecular-induced effects (dissociations), it would be possible to better understand the side effects of radiation, such as induced cancers or damage to healthy tissue. With this in view, this paper presents results of a simulation of a I-seed treatment with an event-by-event MC code (LEPTS) specifically designed to account for the low energy secondary particle interactions, such as electron attachment, vibro-rotational and neutral dissociation interactions. This calculation allowed us to analyze the potential radiation damage not only in connection with the energy deposition, but also in terms of induced molecular dissociations by taking into account ionizing and non-ionizing dissociative processes. We propose that this description of the molecular level damage be the basis for nanodosimetric evaluations., This work was supported by MINECO (FIS2012-31230) and FCT/MEC, RaBBiT, PD-F, PD/00193/2012; UID/Multi/04378/2013(UCIBIO); UID/FIS/00068/2013 (CEFITEC); and FCTMCTES Grant no.SFRH/BD/52536/2014

10 pags., 5 figs., 3 tabs., Experimental measurements of the cations created in electron impact ionization have been undertaken for the primary isomer of propanol using a Hidden Quadrupole Mass Spectrometer (EPIC 300), with a mass resolution of 1 amu. The mass spectra recorded at an incident electron energy of 70 eV reveals the relative probability of forming 50 different cations, by either direct ionization or dissociative ionization. Individual partial ionization cross sections (PICS) for 31 different cations were measured for the first time in this work, for the incident electron energy range from 10 to 100 eV. Also, appearance energies (AEs) and Wannier exponents for the 16 most intense cations formed in electron collisions with 1-propanol are reported. Where possible, those results are compared to those from an earlier investigation. Total Ionization Cross Sections (TICS) were also obtained from the sum of the measured PICS, for nearly all cations measured, and are compared to relevant data reported in the literature. In addition, as a part of this study, theoretical TICS were calculated using the Binary-encounter Bethe (BEB) and independent atom model with screening corrected additivity rule (IAM–SCAR) methods. Good agreement between current measured and calculated TICSs and corresponding earlier results was typically found., M.C.A.L. acknowledges financial support from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq),Fundacão de Amparo à Pesquisa do Estado de Minas Gerais(FAPEMIG) and FINEP (under project CT-Infra), while M.J.B. thanks CNPq for his “Special Visiting Professor” award. K.L.N. thanks CNPq for an “Attracting Young Talent Grant” under the “Science WithoutBorders” program. Some financial assistance from the Australian Research Council is also noted. Finally, S. Ghosh acknowledges forhis grant from PNPD/CAPES while G. Garcia thanks the Spanish Ministerio de Economia, Industria y Competitividad for his projectgrant FIS 2016 −80440 and the EU project FP7-ITN – ARGENT –608163.

7 págs.; 6 figs., © 2015 Elsevier B.V. All rights reserved. The independent atom model representation (IAM) in combination with the additivity rule (AR) is customary accepted as a good approximation to describe electron and positron scattering processes with polyatomic molecules at intermediate and high energies (typically above 100 eV). Within this approach, interference terms are not properly evaluated and are usually ignored in the cross section calculations. However, through a numerical solution of the Lippmann-Schwinger equation for three dimensional multicentre potentials we here demonstrate how interference terms can affect to the calculated differential and integral cross section values even at such relatively high energies. Practical corrections to the AR approach for both differential and integral electron and positron scattering cross section calculations from molecules are also proposed., This study has been partially supported by the Spanish Ministerio de Economía y Competitividad (project FIS2012-31230).

5 págs.; 4 figs., An improvement of the screening-corrected Additivity Rule (SCAR) is proposed for calculating electron and positron scattering cross sections from polyatomic molecules within the independent atom model (IAM), following the analysis of numerical solutions to the three-dimensional Lippmann-Schwinger equation for multicenter potentials. Interference contributions affect all the considered energy range (1-300 eV); the lower energies where the atomic screening is most effective and higher energies, where interatomic distances are large compared to total cross sections and electron wavelengths. This correction to the interference terms provides a significant improvement for both total and differential elastic cross sections at these energies. © 2015 Elsevier B.V. All rights reserved, This study has been partially supported by the Spanish Ministerio de Economía y Competitividad (project FIS2012-31230) and the EU COST programme (Action CM1301). L.E.-G. is supported by the EU FP7-PEOPLE-2013-ITN programme (ARGENT project).

7 pags.; 5 figs., In this paper we make a parallel between the swarm method in physics of ionized gases and modeling of positrons in radiation therapy and diagnostics. The basic idea is to take advantage of the experience gained in the past with electron swarms and to use it in establishing procedures of modeling positron diagnostics and therapy based on the well-established experimental binary collision data. In doing so we discuss the application of Monte Carlo technique for positrons in the same manner as used previously for electron swarms, we discuss the role of complete cross section sets (complete in terms of number, momentum and energy balance and tested against measured swarm parameters), we discuss the role of benchmarks and how to choose benchmarks for electrons that may perhaps be a subject to experimental verification. Finally we show some samples of positron trajectories together with secondary electrons that were established solely on the basis of accurate binary cross sections and also how those may be used in modeling of both gas filled traps and living organisms. © 2013 Elsevier Ltd., This work was supported by the MNTR, Serbia, under Contracts ON171037, III41011 and SANU155.

8 pags.; 7 figs.; 3 tabs., Clustering effects in the differential and integral electron scattering cross sections have been investigated by calculating their magnitudes for different water cluster configurations: specifically for the dimer, trimer and tetramer. By assuming that condensation effects can be described in terms of modifications to the single molecule electron scattering cross sections, induced by the surrounding molecules, effective data for liquid water is also provided. Comparison with previous calculations in liquid water has been carried out through the inelastic mean free path, i.e. the mean length between successive inelastic collisions. Although a satisfactory agreement for high energies, above 100 eV, has been found, for lower energies some discrepancies remain and so will be the subject of further investigation. As an example of modelling electron interactions in soft matter, the present set of data has been employed to simulate single electron tracks in liquid water. This was achieved using our Low Energy Particle Track Simulation (LEPTS) code. © 2014 Elsevier B.V., This work is partially supported by the Spanish Ministerio de Economía y Competitividad (Project FIS2012-31320).

9 pags.; 6 figs.; 1 app., We present a study of electron and positron transport in water in both the gaseous and liquid states using a Boltzmann equation analysis and a Monte-Carlo simulation technique. We assess the importance of coherent scattering processes when considering transport of electrons/positrons in dense gases and liquids. We highlight the importance of electron and positron swarm studies and experiments as a test of the accuracy and completeness of cross-sections, as well as a technique for benchmarking Monte-Carlo simulations. The thermalization of low-energy positrons (, G.G. was partially supported by the Spanish Ministerio de Economia e Innovacion (Project FIS2009-10245).

We report gas phase studies on NCO- fragment formation from the nucleobases thymine and uracil and their N-site methylated derivatives upon dissociative electron attachment (DEA) and through electron transfer in potassium collisions. For comparison, the NCO- production in metastable decay of the nucleobases after deprotonation in matrix assisted laser desorption/ionization (MALDI) is also reported. We show that the delayed fragmentation of the dehydrogenated closed-shell anion into NCO- upon DEA proceeds few microseconds after the electron attachment process, indicating a rather slow unimolecular decomposition. Utilizing partially methylated thymine, we demonstrate that the remarkable site selectivity of the initial hydrogen loss as a function of the electron energy is preserved in the prompt as well as the metastable NCO- formation in DEA. Site selectivity in the NCO- yield is also pronounced after deprotonation in MALDI, though distinctly different from that observed in DEA. This is discussed in terms of the different electronic states subjected to metastable decay in these experiments. In potassium collisions with 1- and 3-methylthymine and 1- and 3-methyluracil, the dominant fragment is the NCO- ion and the branching ratios as a function of the collision energy show evidence of extraordinary site-selectivity in the reactions yielding its formation. [Figure not available: see fulltext.] © 2013 American Society for Mass Spectrometry., The authors acknowledge support for this work from the FWF, Wien (P-22665) and the European Commission, Brussels. G.G. aknowledges suppor for the Spanish Ministerio de Economía y Productividad (Project FIS2009-10245)

Elastic electron scattering from gaseous formamide (H2NCHO) has been investigated. Absolute elastic differential cross sections (DCSs) were determined both experimentally and theoretically. The measurements were performed using a cross beam technique, for the incident energies of 100, 150 and 300 eV and scattering angles from 20 degrees to 110 degrees. Relative elastic DCSs were measured as a function of the angle and the absolute DCSs were determined using the relative flow method. The calculations of electron interaction cross sections are based on a corrected form of the independent-atom method, known as the SCAR (screen corrected additivity rule) procedure and using an improved quasifree absorption model. Calculated results agree very well with the experiment. 2011 Elsevier B.V. All rights reserved., The work was supported by the Ministry of Education and Science of Republic of Serbia (Project No. 181020) and Spanish Ministerio de Ciencia e Innovación Project FIS2009-10245, and motivated by COST projects ECCL (CM0601) and Nano-IBCT(MP1002).

Interactions between 1 and 4 keV anions (H -, O -, and OH -) and gas-phase molecules (nitromethane, water, ethanol, and methanol) have been studied using quadrupole mass spectrometry of the product anions and cations. The low collision velocities (0.07-0.40 v Bohr) provide favourable conditions for electron transfer from the anion projectile to the neutral target molecule yielding negative ion formation, while strong competition with cation formation is also observed. Relative production of fragment cations increases with H - impact energy and with projectile mass when energy is constant. Considered together, these results suggest a momentum dependence on collisional energy deposition. As far as negative ion production is concerned, comparisons with previous free electron attachment studies are drawn as a starting point for the interpretation of the anion fragmentation channels. For nitromethane and water, the present anion fragmentation patterns are substantially different to the free electron attachment data. Conversely the fragmentation channels of ethanol and methanol anions only show clear dependence on the electron attachment/transfer process in terms of the relative anion yields. © 2011 Elsevier B.V. All rights reserved., The authors wish to acknowledge the ITS-LEIF network, Ion Technology and Spectroscopy with Low Energy Ion beam Facilities, Transnational Access, Integrating Activities and Accompanying Measures, Integrated Infrastructure Initiative-I3, 6th FP, ITS LEIF-BH-2005-003, 2006–2009. D.A. and R.A. wish to acknowledge the Portuguese Foundation for Science and Technology (FCT-MCTES) for post-graduate scholarships SFRH/BD/61645/2009 and SFRH/BD/32271/2006, respectively.

A simple illustrative physical model is presented to describe the kinetics of damage and amorphization by swift heavy ions (SHI) in LiNbO3. The model considers that every ion impact generates initially a defective region (halo) and a full amorphous core whose relative size depends on the electronic stopping power. Below a given stopping power threshold only a halo is generated. For increasing fluences the amorphized area grows monotonically via overlapping of a fixed number N of halos. In spite of its simplicity the model, which provides analytical solutions, describes many relevant features of the kinetic behaviour. In particular, it predicts approximate Avrami curves with parameters depending on stopping power in qualitative accordance with experiment that turn into Poisson laws well above the threshold value. © 2010 Elsevier B.V. All rights reserved., We acknowledge funding from the Spain’s MICINN Project: MAT-2008-06794-C03-03.

The present study introduces LEPTS, an event-by-event Monte Carlo programme, for simulating an ophthalmic 106Ru/106Rh applicator relevant in brachytherapy of ocular tumours. The distinctive characteristics of this code are the underlying radiation-matter interaction models that distinguish elastic and several kinds of inelastic collisions, as well as the use of mostly experimental input data. Special emphasis is placed on the treatment of low-energy electrons for generally being responsible for the deposition of a large portion of the total energy imparted to matter. © 2011 Elsevier Ltd., This study has been partially supported by the Ministerio de Ciencia e Innovación (Project FIS2009-10245) and the EU Framework Programme (COST Action MP1002).

Texto completo, borrador., We present a MonteCarlo approach to the non-radiative exciton-decay model recently proposed to describe ion-beam damage in LiNbO3 produced in the electronic excitation regime. It takes into account the statistical (random) spatial distribution of ion impacts on the crystal surface. The MonteCarlo approach is necessary to simulate the evolution of the damage morphology with irradiation fluence from the single track regime to the overlapping track regime. A detailed comparison between the morphologies found for sub-threshold and above threshold irradiations is presented. Moreover, a good representation of the Avrami’s type kinetics for amorphization has been achieved and it is in fair accordance with experiment. For moderate fluences where homogeneous amorphous layers are generated, the new approach predicts that the amorphous and crystalline layers are separated by a diffuse (thick) boundary that includes a mixed amorphous-crystalline composition., We acknowledge financial support from the Spanish Ministery of Science and Innovation for the projects MAT-2005-06359-C03-02 and MAT-2008-06794-C03-03. A. Rivera thanks the I3P program of CSIC for financial support.

Electron interaction cross sections with methane have been collected from literature in order to recommend an extensive data set ranging from 0.1-10 000 eV. We have calculated total and elastic cross sections. Complementary experimental electron energy loss distributions covering a wide energy range (20-3000 eV) were measured using two different experimental setups and are here presented for the first time. Bringing together these new contributions and existing information, an interaction model at the molecular level for electrons in CH4 is developed in the form of a Monte Carlo simulation. Finally, we use this to calculate the stopping power of methane and compare it with tabulated data provided by the NIST database. © 2010 Elsevier B.V. All rights reserved., This study has been partially supported by the following research projects and institutions: Ministerio de Educación y Ciencia (Plan Nacional de Física, Project FIS2006-00702), European Science Foundation (COST Action CM0601 and EIPAM Project), Acciones Integradas Hispano-Portuguesas (Project HP2006-0042). We acknowledge technical support from the Spanish National Institute for Fusion Research of CIEMAT.

The SCAR and EGAR procedures have been proposed in order to extend to lower energies the applicability of the additivity rule for calculation of electron-molecule total cross sections. Both those approximate treatments arise after considering geometrical screening corrections due to partial overlapping of atoms in the molecule, as seen by the incident electrons. The main features, results and limitations of both treatments are put here in comparison by means of their application to some different sized species. © 2010 Elsevier B.V. All rights reserved., This work has been partially supported by project BFM 2000- 0012 Promoción General del Conocimiento. J. Rosado acknowledges a PhD grant from “Universidad Complutense de Madrid”

A theoretical strategy is developed to quantitatively assess the ion-beam damage as measured by Rutherford-backscattering spectrometry under channeling conditions (RBS/C) in LiNbO3 crystals. The approach is based on a recent exciton decay model to calculate the concentration of defects generated by the incoming ions as a function of their stopping power. To describe the channeled RBS yield the model takes into account the amorphous (core) as well as the defective halo contributions to the defect tracks caused by the ion impacts. It is concluded that the halo may significantly influence the assessed damage. © 2009 Elsevier B.V. All rights reserved.

A model to account for the defects generated by ion irradiation in the electronic loss regime, and based on non-radiative decay of self-trapped excitons, is discussed and compared to experiments. It takes into account the competing role of the light-emission (radiative) and defect-creation (non-radiative) decay channels. Calculations are applied to LiNbO3, a useful electro-optic crystal, where a large number of relevant experimental data are available. The model explains the strong nonlinear dependence of the defect creation rates as a function of electronic stopping power (thresholding behavior). It also satisfactorily accounts for the formation and growth of amorphous layers by ion-beam irradiation at moderate fluences, φ>1013 cm-2. Moreover, it also provides the right trend and reasonable quantitative accordance to data showing the dependence of the track radius on stopping power in single-impact experiments. Finally, the model determines the light emission yield during irradiation. In particular, it predicts that the number of photons emitted by ion impact first increases and then decreases monotonically with increasing electronic stopping power. © 2007 Elsevier B.V. All rights reserved., A.R. acknowledges financial support from the Spanish MEC through the program Juan de la Cierva.

We review recent results on a novel method to modify crystalline dielectric materials and fabricate optical waveguides and integrated optics devices. It relies on irradiation with medium-mass high-energy ions (2-50 MeV) where the electronic stopping power is dominant over that one associated to nuclear collisions. By exploiting the processing capabilities of the method, novel optical structures can be achieved at moderate (1014 cm-2) and even low and ultralow (1012 cm-2) fluences. In particular, step-like waveguides with a high index jump Δn ∼ 0.1-0.2, guiding both ordinary and extraordinary modes, have been prepared with F and O ions (20 MeV) at moderate fluences. They present good non-linear and electrooptic perfomance and low losses. (1 dB/cm). Moreover, useful optical waveguiding has been also achieved at ultralow frequencies (isolated track regime), using Cl and Si ions (40-45 MeV). In this latter case, the individual amorphous nanotracks, whose radius increases with depth, create an effective optical medium causing optical trapping. © 2007 Elsevier B.V. All rights reserved., We acknowledge funding from the Spain´s MEC project: MAT2005-06359-CO3. A. Garcı´a-Navarro acknowledges the financial support of the MEC through a FPU Fellowship and of the Madrid City Hall-Residencia de Estudiantes.

9 pages, 1 table, 1 scheme.-- Available online 10 January 2003., The synthesis of nine new esters of norethisterone (17α-ethynyl-17β-hydroxyestr-4-en-3-one) is described, with the esterifying acids bearing an acetylenic or olefinic function in a chain of eight or nine carbon atoms, for evaluation as long-acting contraceptive agents., We thank the World Health Organization for financial support of this work.