Electronic Stopping Power Research Articles

Fullerene irradiation leading to track formation enclosing nitrogen bubbles in GaN material

Gallium nitride was irradiated with fullerene projectiles having an electronic stopping power above the threshold required to promote ion track formation. The structural and chemical changes induced by fullerene irradiation were studied through Transmission Electron Microscopy (TEM). High resolution TEM inquiries were performed to identify the structural order along the ion tracks and the strain induced in the lattice neighboring the ion tracks. The TEM investigation pointed out local amorphization inside the whole tracks and High Resolution TEM studies in the track periphery evidence local stress in the wurtzite structure. Chemical investigations were carried out by STEM Electron Energy Loss Spectroscopy (EELS) to describe the chemical order in the neighboring and inside the ion path. Ga/N stoichiometry is essentially maintained in the track core, whereas an oxidation is detected in the ion track, at the surface. Furthermore, the nitrogen k near-edge fine structure investigation reveals the encapsulation of nitrogen bubbles inside the ion tracks.

The Effect of Form Factor Shape on the Nuclear Stopping Power of Calcium, Iron, Zirconium, and Lead Elements

This paper examined the effect of the form factor of the nucleus and its type on the nuclear stopping power of Ca – 40, Fe – 56, Zr – 90, and Pb – 206 isotopes, respectively. The collision, radiative, and total electronic stopping power of these elements was also calculated. The results of the electronic stopping power showed that the collision part exceeds the radiative up to a specific energy that depends on the element’s atomic number, after which the electronic stopping power will prevail. As for the nuclear stopping power of electrons, the results indicated its great dependence on the form factor of the nucleus, but this dependence begins at a specific energy for each studied isotope and this energy changes with the isotope change. Also, the results did not show distinct significant differences between the different types of form factors, which are exponential, geometric, and uniform. On the whole, the results of the nuclear stopping power containing the exponential form factor are decreased by increasing the mass number of the isotopes. Finally, the behavior of the electronic and nuclear stopping powers as a function of the incident electron energy of the studied elements and isotopes behaved like what is expected and known.

Ab initio electronic stopping power for protons in Ga0.5In0.5P/GaAs/Ge triple-junction solar cells for space applications.

Motivated by the radiation damage of solar panels in space, firstly, the results of Monte Carlo particle transport simulations are presented for proton impact on triple-junction Ga0.5In0.5P/GaAs/Ge solar cells, showing the proton projectile penetration in the cells as a function of energy. It is followed by a systematic ab initio investigation of the electronic stopping power (ESP) for protons in different layers of the cell at the relevant velocities via real-time time-dependent density functional theory calculations. The ESP is found to depend significantly on different channelling conditions, which should affect the low-velocity damage predictions, and which are understood in terms of impact parameter and electron density along the path. Additionally, we explore the effect of the interface between the layers of the multilayer structure on the energy loss of a proton, along with the effect of strain in the lattice-matched solar cell. Both effects are found to be small compared with the main bulk effect. The interface energy loss has been found to increase with decreasing proton velocity, and in one case, there is an effective interface energy gain.

Electron Stopping Powers of Chitin and Chitosan

Chitosan can be deduced from chitin by simple chemical process. Chitosan has many applications and one of the promise application is used as nuclear shield by adopted it with some materials. Electron stopping power (SP) represents important parameter in tested the ability of any material to use it as nuclear shield. Therefore, stopping powers of electrons incident with different energies on chitin and chitosan have been calculated by using codes of National Institute of Standards and Technology (NIST) after modified it by built in the chemical structure and some other properties of chitin and chitosan in the codes. The results of total SP showed that chitosan has values larger than chitin but the differences are small and the maximum percentage difference ratio is 6.8% at 4 MeV electron energy. Total SP has approximately 35 Mev.cm2/g at 0.01 MeV electron energy, and decreasing with energy till to 1 MeV, then slowly increasing. In addition to total SP, the collision SP, radiative SP, density effect parameter, radiation yield, and electron range were calculated. The behaviors of the calculated parameters have been studied and explained. The obtained results suggested that chitosan may be used after mixing it with other materials as a shield from nuclear radiation, especially in low energies.

Contribution of Autoionization Processes to the Electronic Stopping Power

It is shown that the excitation of autoionization states during the collisions of keV-energy ions with a solid plays a determining role in the formation of inelastic energy losses and, accordingly, the electronic-stopping cross section Se. It is proposed to estimate the Se values using the relationship between the cross section for autoionization-state excitation and the ionization cross section. For cases where the ionization cross sections are unknown, scaling is used to calculate the ionization cross sections when the L and M shells are excited. The threshold dependence of Se versus the energy of bombarding ions is predicted.

Parametric study of the Two-Temperature Model for Molecular Dynamics simulations of collisions cascades in Si and Ge

The sensitivity of collision cascades simulations to the Two-Temperature Model main parameters is investigated by performing an extensive statistical study both in Si and Ge materials. The purpose is to identify the parameters of the Two-Temperature Model whose impact is the most significant on the cascades properties and to discuss the physical role of each parameter. We demonstrate that the electronic stopping power and electron–phonon coupling have a drastic impact both in Si and Ge but that these two parameters act differently on those two materials due to their distinct thermal properties. We show that the formation of thermal spikes and therefore of amorphous pockets is sensitive to the electronic specific heat. The effects are again very distinct in Si and in Ge. The influence of both the threshold velocity for the stopping power and the electron–phonon coupling activation time are found to be negligible at the considered energies.

Fullerene Irradiation Leads to Track Formation Enclosing Nitrogen Bubbles in GaN Material

Gallium nitride was irradiated with fullerene projectiles having an electronic stoppingpower above the threshold needed to promote ion track formation. The structural andchemical changes induced by fullerene irradiation were studied though TransmissionElectron Microscopy (TEM). High resolution TEM inquiries were performed to identifythe structural order along the ion tracks and the strain induced in the latticeneighboring the ion tracks. The TEM investigation pointed out local amorphizationinside the whole tracks and High Resolution TEM studies in the track peripheryevidence local stress in the wurtzite structure. Chemical investigations were carried outby STEM - Electron Energy Loss Spectroscopy (EELS) to describe the chemical orderin the neighboring and inside the ion path. Chemical profiles plotted across ion tracksindicate that the Ga/N stoichiometry is essentially maintained in the core track, anoxidation in the ion track periphery was also detected at the surface. Furthermore, thenitrogen k near-edge fine structure investigation reveals the encapsulation of nitrogenbubbles inside the ion tracks.

Quantifying the impact of an electronic drag force on defect production from high-energy displacement cascades in α-zirconium

Molecular dynamics displacement cascade simulations with PKA energies up to 40 keV at 600 K have been performed to investigate the impact of electronic energy losses in α-zirconium. The following data sets are compared: 1) displacement cascades performed with nuclear stopping only and 2) displacement cascades with simultaneous nuclear and electronic stopping. Electronic energy losses are modeled by a drag force with strength proportional to the energy-dependent electronic stopping power using the intrinsic “fix electron/stopping” command in LAMMPS. Consistent with typical characteristics of cascade defect generation, the production efficiency of Frenkel pairs falls below 20% of the NRT-predicted value for high PKA energies, defect clustering increases with PKA energy, and two distinct power-law regimes of the form NF=A(Ep)mcorrelate the surviving number of Frenkel pairs; the separate power-law fits describe defect production prior to and following sub-cascade formation. When implemented, electronic energy losses account for a 10–20% reduction in surviving Frenkel pairs for high-energy PKAs. The energy loss method implemented in LAMMPS results in nuclear damage energies comparable with the values predicted by SRIM using the full-cascade option, and represents a user-friendly method to incorporate ionization losses in molecular dynamics simulations.

Radiolysis of NH3:CO ice mixtures – implications for Solar system and interstellar ices

ABSTRACT Experimental results on the processing of NH3:CO ice mixtures of astrophysical relevance by energetic (538 MeV 64Ni24+) projectiles are presented. NH3 and CO are two molecules relatively common in interstellar medium and Solar system; they may be precursors of amino acids. 64Ni ions may be considered as representative of heavy cosmic ray analogues. Laboratory data were collected using mid-infrared Fourier transform spectroscopy and revealed the formation of ammonium cation (NH$_4^+$), cyanate (OCN−), molecular nitrogen (N2), and CO2. Tentative assignments of carbamic acid (NH2COOH), formate ion (HCOO−), zwitterionic glycine (NH$_3^+$CH2COO−), and ammonium carbamate (NH$_4^+$NH2COO−) are proposed. Despite the confirmation on the synthesis of several complex species bearing C, H, O, and N atoms, no N–O-bearing species was detected. Moreover, parameters relevant for computational astrophysics, such as destruction and formation cross-sections, are determined for the precursor and the main detected species. Those values scale with the electronic stopping power (Se) roughly as σ ∼ a S$_\mathrm{ e}^n$, where n ∼ 3/2. The power law is helpful for predicting the CO and NH3 dissociation and CO2 formation cross-sections for other ions and energies; these predictions allow estimating the effects of the entire cosmic ray radiation field.

Effects of atom–electron energy exchange on radiation damage in zirconium

Abstract Molecular dynamics (MD) is an important tool for investigating primary radiation damage in materials. Electronic effects, including electronic stopping power ( s e ) and electron–phonon coupling (EPC), have a significant influence on high-energy radiation damage in many metals. Based on MD, this study investigated the role played by electronic effects on the collision cascade in α-zirconium (α-Zr). The results show that when the dominant type of cascades is unconnected subcascades, EPC obviously affects the evolution of collision cascades. The incorporation of EPC can promote the generation of subcascades, which reduces large defect clusters. Furthermore, more defects survive when EPC is applied, where the number of residual defects increases with the capacity of EPC. In contrast, the application of s e on low-energy atoms impels the aggregation of the defects into large clusters. However, both EPC and s e only slightly affect the spatial distribution of the defect clusters. The influence of cutoff energy choice on the simulation results was also discussed.

Electronic stopping in molecular dynamics simulations of cascades in 3C–SiC

We investigate the effect of the electronic stopping power on defect production due to ion irradiation of cubic silicon carbide using molecular dynamics simulations. We simulate 20 keV and 30 keV Si and C ions, with and without the electronic energy loss. The results show that the electronic stopping effects are more profound in the case of C irradiation, where the ratio of the electronic energy loss Se to the nuclear energy loss Sn is much larger compared to the ratio for Si ions. These findings indicate that this ratio plays a role in the effect of the electronic stopping on ion irradiation.

Effect of chemical disorder on the electronic stopping of solid solution alloys

The electronic stopping power of nickel-based equiatomic solid solutions alloys NiCr, NiFe and NiCo for protons and alpha projectiles is investigated in detail using real-time time-dependent density functional theory over a wide range of velocities. Recently developed numerical electronic structure methods are used to probe fundamental aspects of electron-ion coupling non-perturbatively and in a fully atomistic context, capturing the effect of the atomic scale disorder. The effects of particular electronic band structures and density of states reflect in the low velocity limit behavior. We compare our results for the alloys with those of a pure nickel target to understand how alloying affects the electronic stopping. We discover that NiCo and NiFe have similar stopping behavior as Ni while NiCr has an asymptotic stopping power that is more than a factor of two larger than its counterparts for velocities below 0.1 a.u.. We show that the low-velocity limit of electronic stopping power can be manipulated by controlling the broadening of the d-band through the chemical disorder. In this regime, the Bragg’s additive rule for the stopping of composite materials also fails for NiCr.

Electronic stopping power under channeling conditions for slow ions in Ge using first principles

The electronic stopping power for low-velocity ions (including protons and $\ensuremath{\alpha}$ particles) in the semiconductor Ge is investigated with the aid of time-dependent density functional theory based on Ehrenfest dynamics. The purpose of this study is to further learn about the energy loss mechanisms of the slow ions. When the projectile ions pass through the crystal film along the $\ensuremath{\langle}100\ensuremath{\rangle}, \ensuremath{\langle}110\ensuremath{\rangle}$, and $\ensuremath{\langle}111\ensuremath{\rangle}$ channels, we analyze the channeling effect of the electronic stopping power in detail by investigating the channeling electronic density, the stopping force, and the trapped electrons. Our results are in good agreement with the available experimental data and the other theoretical calculations, which demonstrate that this approach is able to reasonably describe the electronic stopping power. Furthermore, these results can act as the reference data for the ion-beam irradiation of Ge in the low-energy regime.

Photon and electron attenuation parameters of phosphate and borate bioactive glasses by using Geant4 simulations

This paper aims to study the photon and electron attenuation parameters of phosphate and borate bioactive glasses such as 45P2O5–55Li2O, 50P2O5–50Li2O, 55B2O3–45Li2O, and 2.6P2O5-46.1SiO2-24.4Li2O-26.9CaO. Geant4 toolkit was carried out to simulate the interactions of photon and electron with the glasses at medical diagnostic energies between 30 keV and 80 keV. The correct implementation of the simulation values was confirmed by using the corresponding values calculated from the Phy-X program. Photon attenuation studies were achieved by evaluating linear and mass attenuation coefficients (μ, μ/ρ), effective atomic number for total photon interaction (Zeff), and half value layer (HVL). Electron attenuation studies were investigated by determining the electron stopping power (Ψ) for each glass sample. Moreover, the mean energy deposited (dE/dx) in the glass sample was estimated for photon and electron interactions. The results showed that the chemical composition of the glass has a strong influence on the photon interactions and weak influence on the electron interactions. Furthermore, the maximum dE/dx values were observed at 30 keV and 80 keV for the photon interactions and electron interactions, respectively.

Electronic sputtering of SiC and KBr by high energy ions

We have measured electronic sputtering yields of SiC and KBr by high-energy ions (198 MeV Xe, 99 MeV Xe, 89 MeV Ni, 60 MeV Ar and 55 MeV Cl ions with the equilibrium charge). Employing the carbon-foil collector method, sputtered atoms in the C-foil are analyzed by Rutherford backscattering spectrometry (RBS) and the sputtering yields have been evaluated. It appears that the sputtering yields Y follow the power-law of the electronic stopping power (Se): Y=(1.86Se)1.53 and Y=(0.77Se)3.0 for SiC and KBr, respectively (Se in keV/nm). The representative sputtering yield at Se = 10 keV/nm is evaluated to be 87.6 and 457 for SiC (bandgap Eg = 2.86 eV) and KBr (Eg = 7.4 eV) and it is revealed that these can be explained within the bandgap scheme. Lattice disordering by ion impact has been also measured by X-ray diffraction (XRD) and Se dependence of the XRD intensity degradation is compared with that of electronic sputtering.

Monte Carlo simulations of electron-sample interactions at phase boundaries and implications for automated mineralogy

Automated mineralogy instrumentation (QEMSCAN, MLA, TIMA) is routinely used for materials characterization in the mining industry. All current techniques identify minerals based on a combination of backscattered electron and chemical (energy-dispersive spectroscopy) signals read from the sample. Boundary zones, where two or more minerals are touching, yield signals that reflect a mix of the characteristics of multiple minerals and that may or may not match anything in the mineral database. These phase boundaries, varying in width, are known to cause errors in automated mineralogy analyses, but what mineral and boundary characteristics affect phase boundary width and how much error phase boundaries can cause remain poorly understood.New Monte Carlo modeling of electron-sample interactions at and near phase boundaries shows that the width of the zone of mixed signals, and hence the amount of error, depends on the grain size and texture of the sample; the densities of the minerals and the ionization potentials of their constituent elements; and the position and orientation of the boundary between the minerals, as well as various instrumental factors such as beam accelerating voltage. Error induced by phase boundaries is high when a high accelerating voltage is used to examine fine-grained samples with complex (intergrowth, exsolution) textures that involve low-density minerals with low-ionization-potential elements. Error is low when the sample is coarse-grained, lacks complex textural relationships that create boundary area, and consists of high-density minerals with high-ionization-potential elements, which have a higher electron stopping power and prevent the beam from spreading out as much. Where low- and high-density minerals are in contact at an angled boundary, the width of the boundary zone is low when the high-density mineral is on top and high when the low-density phase is on top.Calculations based on these simulations indicate that the amount of area that could fall within phase boundary zones depends strongly on grain size, shape, and width of boundary zone. Boundary phases may contribute significantly to overall analytical error for fine-grained minerals with low densities and composed of elements with low ionization potentials, but for most samples the boundary phase area is likely to be <5% of the total surface area and the error relatively small. Errors induced by boundary phases will probably continue to annoy geometallurgists for some time, but with proper laboratory procedures for validating and cross-checking automated mineralogy results, they should not be a major component of error for most samples.

Study of the ionization efficiency for nuclear recoils in pure crystals

We study the basic integral equation in Lindhard's theory describing the energy given to atomic motion by nuclear recoils in a pure material when the atomic binding energy is taken into account. The numerical solution, which depends only on the slope of the velocity-proportional electronic stopping power and the binding energy, leads to an estimation of the ionization efficiency which is in good agreement with the available experimental measurements for Si and Ge. In this model, the quenching factor for nuclear recoils features a cut-off at an energy equal to twice the assumed binding energy. We argue that the model is a reasonable approximation for Ge even for energies close to the cutoff, while for Si is valid up to recoil energies greater than ~500 eV.

Ion irradiation of acetylene ice in the ISM and the outer Solar system: laboratory simulations

ABSTRACT)3 Acetylene, C2H2, has been observed in the interstellar medium, mostly around young stellar objects, as well as in molecular clouds and cometary comae, representing an important species of astrophysical interest. In this work, we present a laboratory study of the C2H2 radiolysis at 45 K for three different beams and energies: 1.0 MeV H+ and He+, and 1.0 and 1.5 MeV N+ beams. Fourier transform infrared spectroscopy was used for monitoring the molecular changes induced by the ion processing. Two different sample thicknesses were irradiated; for the thicker one, implantation had occurred. Spectra and absorbance evolutions for the thin and thick films are qualitatively different. Four C2H2 bands are observed at 3225, 1954, 1392, and 763 cm−1. The C2H2 compaction and apparent destruction cross-sections are determined. For the case of the H+ beam, the compaction cross-section dominates. Concerning molecular synthesis by irradiation, New product bands were not observed in the thin ice irradiations; for the thicker film ice, the daughter species CH4, C2H4, C3H6, and C4H4 have been identified and their destruction and formation cross-sections determined. The apparent destruction cross-section was found to be a function of the electronic stopping power (Se) as σd ∝ S$_\mathrm{ e}^{3/2}$. The half-life of the C2H2 bombarded by galactic cosmic rays is estimated. The current findings are a contribution to the understanding of how the molecules synthesized upon irradiation of Interstellar and outer Solar system ices participate to the molecular enrichment and to the physicochemical evolution of the Universe.

Stopping Power and Partial Stopping Power Effective Charge in The Plasma

The energy losses of ions moving in an electron gas can be studied through the stopping power of the medium. A large number of calculations of the stopping power of ions and electrons in plasmas have been carried out using the random phase approximation (RPA) in the dielectric formalism, for low and high energies. Then we calculated the partial stopping power effective charge (PSPEC) from the energy loss of an incident proton, Ar-ion, and He-ion in target plasma. The Brandt-Kitagawa (BK) model is used to describe the projectile charge fraction (q) and calculate the stopping power and PSPEC, which depends on temperature and electron density ρ(k) of the plasma. This is a topic of relevance to understanding the beam-target interaction in the contexts of particle driven fusion. The presented study is formulated in terms of classical dielectric functions. The programming language Fortran - 90 was used for a required calculation. In the present work, three systems of plasma (Z-pinch, Tokamak, ICF) for different temperatures and densities were covered. Additionally, a comparison has been done with the previous work of plasma.

Impact of a minority relativistic electron tail interacting with a thermal plasma containing high-atomic-number impurities

A minority relativistic electron component can arise in both laboratory and naturally occurring plasmas. In the presence of high-atomic-number ion species, the ion charge state distribution at a low bulk electron temperature can be dominated by relativistic electrons, even though their density is orders of magnitude lower. This is due to the relativistic enhancement of the collisional excitation and ionization cross sections. The resulting charge state effect can dramatically impact the radiative power loss rate and the related Bethe stopping power of relativistic electrons in a dilute plasma.