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Inelastic scattering of electron and light ion beams in organic polymers

We have calculated the inelastic mean free path, stopping power, and energy-loss straggling of swift electron, proton, and α-particle beams in a broad incident energy range in four organic polymers: poly(methyl methacrylate) (PMMA), Kapton, polyacetylene (PA), and poly(2-vinylpyridine) (P2VP). These calculations have been done through a suitable description of their optical properties and its extension into the whole momentum and energy transfer excitation spectrum. For electrons, we take into account the exchange effect between the projectile and the target electrons, while the charge-state fractions have been considered for ions. Our results are compared with other models and with the available experimental data. An excellent agreement with experimental data is obtained in the case of proton and α-particle beams in Kapton and a reasonably good agreement has been achieved for electron beams in PMMA, Kapton, and PA. We have parameterized by means of simple analytical expressions our results for electron b...

Chapter six – Inelastic Collisions of Energetic Protons in Biological Media

Abstract We study the energy deposited by swift proton beams on materials of biological interest, such as liquid water, DNA, and PMMA. An appropriate description of the target energy-loss function, which provides its electronic excitation spectrum, is obtained from available experimental optical data properly extended to non-vanishing momentum transfers. The main magnitudes characterizing the energy-loss distribution of the beam particles in the target are calculated analytically (in the dielectric framework) and compared with available experimental data. The depth–dose distribution of the energy delivered by the proton beam on the biological targets is simulated by the SEICS (Simulation of Energetic Ions and Clusters through Solids) code, which includes the main interaction phenomena between the projectile and the target constituents by means of Molecular Dynamics and Monte Carlo techniques. Also, the proton-beam energy distribution at several depths in the target for liquid water and PMMA are simulated, and finally, the properties of PMMA as a water-equivalent material are discussed.

Water equivalent properties of materials commonly used in proton dosimetry.

The depth-dose distribution of proton beams in materials currently used in dosimetry measurements, such as liquid water, PMMA or graphite are calculated with the SEICS (Simulation of Energetic Ions and Clusters through Solids) code, where all the relevant effects in the evaluation of the energy deposited by the beam in the target are included, such as electronic energy-loss (including energy-loss straggling), multiple elastic scattering, electronic charge-exchange processes, and nuclear fragmentation interactions. Water equivalent properties are obtained for different proton beam energies and several targets of interest in dosimetry.

Radial doses around energetic ion tracks and the onset of shock waves on the nanoscale

Abstract Energetic ions lose their energy in tissue mainly by ionising its molecules. This produces secondary electrons which transport this energy radially away from the ion path. The ranges of most of these electrons do not exceed a few nanometres, therefore large energy densities (radial doses) are produced within a narrow region around the ion trajectory. Large energy density gradients correspond to large pressure gradients and this brings about shock waves propagating away from the ion path. Previous works have studied these waves by molecular dynamics (MD) simulations investigating their damaging effects on DNA molecules. However, these simulations where performed assuming that all energy lost by ions is deposited uniformly in thin cylinders around their path. In the present work, the radial dose distributions, calculated by solving the diffusion equation for the low energy electrons and complemented with a semi-empirical inclusion of more energetic δ-electrons, are used to set up initial conditions for the shock wave simulation. The effect of these energy distributions vs. stepwise energy distributions in tracks on the strength of shock waves induced by carbon ions both in the Bragg peak region and out of it is studied by MD simulations. Graphical abstract

Comparative analysis of the secondary electron yield from carbon nanoparticles and pure water medium

Abstract The production of secondary electrons generated by carbon nanoparticles and pure water medium irradiated by fast protons is studied by means of model approaches and Monte Carlo simulations. It is demonstrated that due to a prominent collective response to an external field, the nanoparticles embedded in the medium enhance the yield of low-energy electrons. The maximal enhancement is observed for electrons in the energy range where plasmons, which are excited in the nanoparticles, play the dominant role. Electron yield from a solid carbon nanoparticle composed of fullerite, a crystalline form of C60 fullerene, is demonstrated to be several times higher than that from liquid water. Decay of plasmon excitations in carbon-based nanosystems thus represents a mechanism of increase of the low-energy electron yield, similar to the case of sensitizing metal nanoparticles. This observation gives a hint for investigation of novel types of sensitizers to be composed of metallic and organic parts. Graphical abstract

A study of the energy deposition profile of proton beams in materials of hadron therapeutic interest

The energy delivered by a swift proton beam in materials of interest to hadron therapy (liquid water, polymethylmethacrylate or polystyrene) is investigated. An explicit condensed-state description of the target excitation spectrum based on the dielectric formalism is used to calculate the energy-loss rate of the beam in the irradiated materials. This magnitude is the main input in the simulation code SEICS (Simulation of Energetic Ions and Clusters through Solids) used to evaluate the dose as a function of the penetration depth and radial distance from the beam axis.

Role of the interaction processes in the depth-dose distribution of proton beams in liquid water

We use a simulation code, based on Molecular Dynamics and Monte Carlo, to investigate the depth-dose profile and lateral radial spreading of swift proton beams in liquid water. The stochastic nature of the projectile-target interaction is accounted for in a detailed manner by including in a consistent way fluctuations in both the energy loss due to inelastic collisions and the angular deflection from multiple elastic scattering. Depth-variation of the projectile charge-state as it slows down into the target, due to electron capture and loss processes, is also considered. By selectively switching on/off these stochastic processes in the simulation, we evaluate the contribution of each one of them to the Bragg curve. Our simulations show that the inclusion of the energy-loss straggling sizeably affects the width of the Bragg peak, whose position is mainly determined by the stopping power. The lateral spread of the beam as a function of the depth in the target is also examined.

New research in ionizing radiation and nanoparticles: the ARGENT project

This chapter gives an overview of “ARGENT ” (“Advanced Radiotherapy , Generated by Exploiting Nanoprocesses and Technologies”) , an ongoing international Initial Training Network project , supported by the European Commission . The project , bringing together world-leading researchers in physics, medical physics, chemistry, and biology, aims to train 13 Early Stage Researchers (ESRs) whose research activities are linked to understanding and exploiting the nanoscale processes that drive physical, chemical, and biological effects induced by ionizing radiation in the presence of radiosensitizing nanoparticles . This research is at the forefront of current practices and involves many experts from the respective scientific disciplines. In this chapter, we overview research topics covered by ARGENT and briefly describe the research projects of each ESR.

Simulation of the ion-induced shock waves effects on the transport of chemically reactive species in ion tracks

The passage of energetic ions through tissue initiates a series of physico-chemical events, which lead to biodamage. The study of this scenario using a multiscale approach brought about the theoretical prediction of shock waves initiated by energy deposited within ion tracks. These waves are being explored in this letter in different aspects. The radial dose that sets their initial conditions is calculated using diffusion equations extended to include the effect of energetic

Transport of secondary electrons through coatings of ion-irradiated metallic nanoparticles

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