Extension of charge-state-distribution calculations for ion-solid collisions towards low velocities and many-electron ions

Knowledge of the detailed evolution of the whole charge-state distribution of projectile ions colliding with targets is required in several fields of research such as material science and atomic and nuclear physics but also in accelerator physics, and in particular in regard to the several foreseen large-scale facilities. However, there is a lack of data for collisions in the nonperturbative energy domain and that involve many-electron projectiles. Starting from the etacha model we developed [Rozet, Nucl. Instrum. Methods Phys. Res., Sect. B 107, 67 (1996)10.1016/0168-583X(95)00800-4], we present an extension of its validity domain towards lower velocities and larger distortions. Moreover, the system of rate equations is able to take into account ions with up to 60 orbital states of electrons. The computed data from the different new versions of the etacha code are compared to some test collision systems. The improvements made are clearly illustrated by 28.9MeVu-1Pb56+ ions, and laser-generated carbon ion beams of 0.045 to 0.5MeVu-1, passing through carbon or aluminum targets, respectively. Hence, those new developments can efficiently sustain the experimental programs that are currently in progress on the "next-generation" accelerators or laser facilities.Fil: Lamour, E.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; FranciaFil: Fainstein, Pablo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Galassi, Mariel Elisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Prigent, C.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; FranciaFil: Ramirez, C. A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Rivarola, Roberto Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Rozet, J. P.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; FranciaFil: Trassinelli, M.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; FranciaFil: Vernhet, D.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; Franci

Preliminar study of the effects of gamma radiations on human red blood cells

En este estudio se analizaron los parámetros viscoelásticos y de agregación en glóbulos rojos humanos sometidos a los procedimientos habituales de irradiación gamma con fines transfusionales. Las muestras fueron irradiadas a diferentes dosis a fin de determinar los posibles cambios hemorreológicos que pudieran afectar a la salud de los pacientes y su relación con las modificaciones bioquímicas observadas. Los resultados obtenidos muestran alteraciones en el tiempo de agregación, en la viscosidad superficial de membrana y en el tamaño de los agregados eritrocitarios en las muestras irradiadas, sugiriendo que el daño producido por la radiación ionizante afecta a las propiedades físicas de la membrana del glóbulo rojo en diferentes nivelesIn this study, the alterations in viscoelastic and aggregation parameters of red blood cells were analyzed for usual gamma irradiation procedures for transfusion purposes. In order to determine possible hemorheological changes that may affect the health of patients and their relationship with the biochemical changes observed, the blood samples were irradiated at different doses. The results show alterations in the erythrocyte aggregation time, in the membrane surface viscosity and in the size of the aggregates in the irradiated samples, suggesting that the damage produced by the ionizing radiation affects the physical properties of red blood cell membrane at different levels.Fil: Estrada, E.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas; ArgentinaFil: Castellini, H.. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; ArgentinaFil: Acosta, A.. Centro Regional de Hemoterapia; ArgentinaFil: Di Tullio, L.. Centro Regional de Hemoterapia de Rosario; ArgentinaFil: Borraz, J.. Centro Regional de Hemoterapia de Rosario; ArgentinaFil: Chinellato, A.. Centro Regional de Hemoterapia de Rosario; ArgentinaFil: Tack, I.. Centro Regional de Hemoterapia de Rosario; ArgentinaFil: D'Arrigo, M.. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; ArgentinaFil: Riquelme, Bibiana Doris. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas; ArgentinaFil: Galassi, Mariel Elisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; Argentin

A single method to calculate multiple ionization cross sections of Air molecules by ion impact

International audienceIn many areas of science and technology the ionization of the molecules that constitute the air by ion impact is of great relevance. In astrophysics, the ionization and dissociation of the air molecules by swift ions impact from cosmic radiation and the solar wind provokes different effects on atmosphere. In medical physics, the reference and relative dosimetry is performed using ionization chambers constituted by a cavity that contains air and an electrometer that determine the charge generated after the pass of the ionizing radiation. The measured values are converted to dose in liquid water by applying different correction factors and physical parameters such as the stopping power ratios air/water and the W-values (energy required to generate an ionic pair) [1]. The ionization processes are of relevance in the computation of these physical parameters for protontherapy and hadrontherapy (ion-beam cancer therapy). In a previous article, multiple ionization cross sections (MICS) of carbon monoxide, nitrogen and oxygen by proton impact were calculated using the Independent Electron Model (IEM), describing the molecules as two atoms at the equilibrium distance [2].In the present work, MICS of air molecules by proton and heavy ion impact are calculated applying the IEM taking into account the molecular character of the target. The molecular orbitals are described using the CNDO (Complete Neglect of Differential Overlap) model [3]. An exponential model is used to represent the single particle ionization probabilities as a function of the impact parameter. The single ionization cross sections required are calculated by applying different theoretical models [3,4]. Auger-type emission is analysed, showing the importance of post-collisional contributions to the MICS at high impact energies. The results are in good agreement with experimental data

Multiple ionization cross sections for swift ion impact on ne-like molecules

References : [1] B. Gervais, M. Beuve, G. Olivera and M. Galassi. Rad. Phys. Chem. 75, 493-513 (2006). [2] R. Rivarola, M.E. Galassi, P.D. Fainstein, C. Champion. Book Series "Advances in Quantum Chemistry: Theory of heavy ion collision physics in hadron therapy". Chapter nine. Elsevier Inc. Copenhagen, Dinamarca. (2013). [3] M.E. Galassi, R.D. Rivarola and P.D. Fainstein. Phy. Rev. A 75, 052708 (2007).International audienceThe study of multiple ionization of molecules by swift ion impact is of great interest in many subfields of physics, chemistry, astrophysics and ion-beam cancer therapy. During the irradiation of human tissues with such ions, the biological molecules are ionized and excited. Mainly, in the region of maximum energy deposition (known as the Bragg’s peak), multi-electron processes occur (transfer-ionization, multiple ionization, etc). Experimental cross sections for multi-electron emission by heavy ion impact on molecules are scarce and the development of predictive accurate theoretical models to calculate multiple-ionization cross sections (MICS) is necessary. In previous works, exclusive MICS of water molecules by ion impact were calculated in the framework of the Independent Particle Model (IPM), employing a binomial distribution in order to take into account contributions from different molecular target orbitals. The single particle probabilities as a function of the impact parameter were calculated using two different methods: the Exponential Model (EM) and the Continuum Distorted Wave - Eikonal Initial State (CDW-EIS) approximation [1-2]. Within the Exponential Model, the single-electron emission probabilities for each shell are described by decreasing exponential functions with adjustable parameters to reproduce net-ionization cross sections. For the case of proton impact on Ne and Ar, MICS-EM was found in remarkable agreement with experimental data [3]. In the present work, we extend the use of the MICS-EM to monocentric Ne-like molecules (H2O, CH4, NH3). The post-collisional contributions, that dominate the MICS at high impact energy, are considered by extending the model used for Ne [3]. We analyze the dependence of MICS with the energy and charge of the projectile. For these light molecules good agreement with experimental data is obtained

Multiple ionization cross sections for swift ion impact on ne-like molecules

References : [1] B. Gervais, M. Beuve, G. Olivera and M. Galassi. Rad. Phys. Chem. 75, 493-513 (2006). [2] R. Rivarola, M.E. Galassi, P.D. Fainstein, C. Champion. Book Series "Advances in Quantum Chemistry: Theory of heavy ion collision physics in hadron therapy". Chapter nine. Elsevier Inc. Copenhagen, Dinamarca. (2013). [3] M.E. Galassi, R.D. Rivarola and P.D. Fainstein. Phy. Rev. A 75, 052708 (2007).International audienceThe study of multiple ionization of molecules by swift ion impact is of great interest in many subfields of physics, chemistry, astrophysics and ion-beam cancer therapy. During the irradiation of human tissues with such ions, the biological molecules are ionized and excited. Mainly, in the region of maximum energy deposition (known as the Bragg’s peak), multi-electron processes occur (transfer-ionization, multiple ionization, etc). Experimental cross sections for multi-electron emission by heavy ion impact on molecules are scarce and the development of predictive accurate theoretical models to calculate multiple-ionization cross sections (MICS) is necessary. In previous works, exclusive MICS of water molecules by ion impact were calculated in the framework of the Independent Particle Model (IPM), employing a binomial distribution in order to take into account contributions from different molecular target orbitals. The single particle probabilities as a function of the impact parameter were calculated using two different methods: the Exponential Model (EM) and the Continuum Distorted Wave - Eikonal Initial State (CDW-EIS) approximation [1-2]. Within the Exponential Model, the single-electron emission probabilities for each shell are described by decreasing exponential functions with adjustable parameters to reproduce net-ionization cross sections. For the case of proton impact on Ne and Ar, MICS-EM was found in remarkable agreement with experimental data [3]. In the present work, we extend the use of the MICS-EM to monocentric Ne-like molecules (H2O, CH4, NH3). The post-collisional contributions, that dominate the MICS at high impact energy, are considered by extending the model used for Ne [3]. We analyze the dependence of MICS with the energy and charge of the projectile. For these light molecules good agreement with experimental data is obtained

Evaluación de la contribucion de electrones Auger y efectos relativistas en la determinación de valores-w por impacto de electrones

International audienceLos valores-W, definidos como la energía media requerida para generar un par iónico en un determinado medio por impacto de radiación ionizante, representan uno de los principales parámetros físicos que intervienen en dosimetría de referencia en radioterapia y hadronterapia [1]. En general, la dosimetría de referencia se realiza utilizando cámaras de ionización que contienen aire a humedad ambiente y un electrómetro que mide el porcentaje de ionización del gas en el interior de dicha cámara. Para pasar estos valores a dosis en agua (medio de referencia) se los debe multiplicar por varios parámetros, entre ellos los valores-W en aire húmedo. Datos experimentales de valores-W por impacto de electrones sobre vapor de agua presentan un perfil constante a energías de impacto altas. Cálculos realizados mediante la ecuación de Fowler [2] (basada en la aproximación de frenado continuo) en los que no se considera la emisión electrónica por Efecto Auger, o correcciones relativistas, no logran reproducir estos resultados experimentales. En el presente trabajo se estudia la contribución de electrones Auger, y el efecto de considerar o no secciones eficaces de ionización por impacto de electrones con corrección relativista.[1] Reporte Técnico RT 398, IAEA (2000)[2] M. Inokuti, Rad. Res. 64, pp. 6-22, (1975

Theoretical study of W-values for particle impact on vapour and liquid water

International audienceCharged particles travelling through a molecular material slow down by collisions with the molecules of the medium. The products of these interactions are either excited molecules or electron-hole pairs, i.e. pairs made of a free electron and the corresponding positive ion resulting from ionization. Additional pairs are produced in further interactions of the liberated electrons in a cascade process. The collection of all the liberated charges forms the basis of ionizing radiation detection in ionization chambers [1]. To determine the dose, conversion factors such as W-values are necessary. They are defined as the mean energy expended by the incident particle to form an electron-hole pair after complete dissipation of its initial energy in the media. This physical parameter represents an important source of uncertainties in hadrontherapy that influences directly the dose determination.The aim of the present work is to study W-values to improve uncertainties and provide values when experimental data are not available. To calculate this parameter, inelastic cross sections and the cumulative counting of all the processes induced by the incident and secondary particles are necessary. As the contribution of secondary electrons to the calculation is of crucial importance for all types of incident particles (electrons, ions, etc.), we started studying W-values by electron impact on liquid and vapour water. We have used two methods: i) the Monte Carlo code MDM [2] which does an event-by-event tracking of all generated particles, and ii) the Fowler Equation based on the Continuous Slowing Down Approximation [3]. The relevance of the cross sections used to describe the ionization and excitation processes is studied. Results are in good agreement with experimental data and theoretical values obtained by other authors. We are working to extend the codes to the case of ion impact on water and air, where charge exchange and multiple ionization must be considered. Preliminary results will be presented

Theoretical study of W-values for particle impact on water

International audienceThe W-values and the differential values w, were calculated by electron, proton and antiproton impact on liquid and vapor water. Two different theoretical approximations were used: the Fowler Equation (based on the Continuous Slowing Down Approximation), and the Monte Carlo code MDM, which does an event-by-event tracking of all generated particles in the media. The dependence on the type and charge of the projectiles and the relevance on the appropriate inelastic cross sections employed in the calculations were studied. For electron impact, results obtained with both models are in good agreement with experimental data and with other theoretical calculations. However, the MDM results are more representative of the stochastic nature of radiation-media interactions. The w-values for swift proton and antiproton impact on vapor water, calculated using the Fowler Equation, are in very good agreement with the results obtained by electron impact in the same velocity regime

Preliminary study of alterations in human red blood cells by irradiation with high energy photons

Introduction: Transfusion-associated graft-versus-host disease can be prevented by treating cellular blood products with gamma irradiation. A wide range of gamma irradiation dose levels are used in routine practice, but gamma irradiation dose of 25 Gy may be required to completely inactivate T cells in Red Blood Cells (RBC) units (Pelszynski, M. et al., 1994). This process decreases the survival of the RBC transfused, so it is crucial to understand the alterations caused by gamma irradiation to the erythrocyte membrane. In previous works, the biochemical and hematological effects of gamma irradiation at different storage periods were studied. It was observed that irradiation of the erythrocytes increases red cells hemolysis and leakage of intracellular potassium (Adams, F. et al., 2015; Yousuf, R. et al., 2018). The mechanisms through which irradiation causes the loss of RBC viability could be related to the primary effects of radiation. Gamma and X-ray Ionizing radiation cause indirect damage through the reactive oxygen species generated by water radiolysis (Anand, A.J. et al., 1997). The reduced deformability of RBC after irradiation could be related to the interaction of the oxygen-derived radicals with the membranes, affecting their mechanical properties and leading to deformability impairment (Kim, Y.-K. et al., 2008). In a recent work (AlZahrani K. et al., 2017), nanoestructural changes in the RBC membrane at different doses of gamma irradiation were observed using atomic force microscopy. The images shown that the roughness of the cell membrane increased dramatically with increasing doses, affecting their biophysical properties. However, more research is needed to understand the effects of gamma irradiation on the mechanical and adhesion properties of RBC. For this reason, in the present work we set out to measure the mechanical and aggregation parameters of human red blood cells exposed to gamma photons in different doses in order to determine the possible alterations due to radiation.Fil: Riquelme, Bibiana Doris. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Física Rosario (IFIR-CONICET); Argentina.Fil: Estrada, Ezequiel. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; Argentina.Fil: Castellini, Horacio V. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; Argentina.Fil: Acosta, Andrea. Centro Regional de Hemoterapia de Santa Fe; Argentina.Fil: Chinelatto, Alejandro. Centro Regional de Hemoterapia de Santa Fe; Argentina.Fil: Tack, Ivan, Ivan. Centro Regional de Hemoterapia de Santa Fe; Argentina.Fil: Borraz, Javier. Centro Regional de Hemoterapia de Santa Fe; Argentina.Fil: Di Tullio, Liliana. Centro Regional de Hemoterapia de Santa Fe; Argentina.Fil: Galassi, Mariel E. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Física Rosario (IFIR-CONICET); Argentina.Fil: Galassi, Mariel E. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; Argentina

Electron Emission from Fragmentation of CO₂ by Fast Proton Impact

Single ionization of CO2 by 6 MeV proton impact has been studied by measuring in coincidence the momentum vectors of the emitted electron and the charged nuclear fragment CO+2, CO+ or O+, respectively. The experimental data have been compared with the predictions of a state of the art CDW-EIS (continuum distorted wave-eikonal initial state) calculation for molecular orbitals. A good qualitative agreement is observed even though the vibrational motion of the molecule is not taken into account in the model. The low-energy electron spectra show a rich structure which may be attributed to the presence of molecular excitation channels which undergo radiationless decay, via autoionization and also via predissociation. This interpretation is supported by photoionization studies of CO2