Total Ionization Research Articles

Radiation-induced effects on the RIGEL ASIC

This paper describes the radiation tests performed on the RIGEL, the Application-Specific Integrated Circuit (ASIC) designed within the scope of the PixDD project, whose goal is the production of a multi-pixel silicon-based detector system to be placed at the focal plane of X-ray optics on board space astronomy missions. Carried out at the RADiation Effects Facility of the University of Jyväskylä (Finland), the campaign aimed at studying the response of the ASIC to radiation damage, in the form of both Total Ionising Dose and Single Event Effects, especially latch-ups and bit upsets. Experimental results were then combined with simulations of the space environment for a low-inclination equatorial orbit and for a Sun-synchronous orbit. The analysis shows that the device under study may be safely operated on an equatorial orbit without any circuitry to protect it from transient radiation phenomena, whereas the need of such a precaution is necessary in the case of a Sun-synchronous orbit. According to the experimental results, the degradation due to Total Ionising Dose, measured in terms of Equivalent Noise Charge, stays below 10% up to 34krad, implying that it can be managed or neglected altogether for the simulated orbits.

X-Ray Induced Total Ionization of Air

X-ray-induced total ionization of air is investigated by solving rate equations of atoms and ions of nitrogen and oxygen. Time distributions of components in the whole ionization process are given by recording respective number density. A clear population inversion is observed as we change the blackbody temperature <inline-formula> <tex-math notation="LaTeX">$T_{b}$ </tex-math></inline-formula> of the incident X-ray. Total ionization time <inline-formula> <tex-math notation="LaTeX">$t_{\mathrm{ end}}$ </tex-math></inline-formula> of the whole system and each ion succession is calculated. We find that <inline-formula> <tex-math notation="LaTeX">$t_{\mathrm{ end}}$ </tex-math></inline-formula> is sensitive to <inline-formula> <tex-math notation="LaTeX">$T_{b}$ </tex-math></inline-formula> of the incident X-ray and an optimal ionization temperature <inline-formula> <tex-math notation="LaTeX">$T_{\mathrm{ opt}}$ </tex-math></inline-formula> exists at which <inline-formula> <tex-math notation="LaTeX">$t_{\mathrm{ end}}$ </tex-math></inline-formula> reaches its minimum. We have given the <inline-formula> <tex-math notation="LaTeX">$T_{\mathrm{ opt}}$ </tex-math></inline-formula> of nitrogen and oxygen ionization, respectively. The result indicates that deviation from the <inline-formula> <tex-math notation="LaTeX">$T_{\mathrm{ opt}}$ </tex-math></inline-formula> will lead to a severe multiplication of total ionization time.

Electron ionisation of cyanoacetylene: ionisation cross sections and dication formation

Cyanoacetylene (HC3N) is an important trace species in the atmosphere of Titan. We report, for the first time, absolute partial electron ionisation cross sections and absolute precursor-specific partial electron ionisation cross sections for cyanoacetylene, following an experimental and computational investigation. Our methodology involves using 2D ion–ion coincidence mass spectrometry to generate relative cross sections, over the electron energy range 50–200 eV. These relative values are then normalised to an absolute scale, using a binary encounter-Bethe (BEB) calculation of the total ionisation cross section. The BEB calculation agrees well with previous determinations in the literature. The mass spectrometric observations of HC2N+ and HCN+, ions with a connectivity markedly different to that of the neutral molecule, point towards a rich cationic energy landscape possessing several local minima. Indeed, [HC3N]2+ minima involving a variety of cyclic configurations are revealed by a preliminary computational investigation, along with two minima with linear and bent geometries involving H atom migration (CCCNH2+). Determination of the energy of a transition state between these local minima indicates that the dication is able to explore the majority of this rich conformational landscape at our experimental energies. This investigation of the energetics also determines an adiabatic double ionisation energy of 30.3 eV for the lowest lying singlet state of HCCCN2+, and 30.1 eV for the lowest-lying triplet state. The bulk of the cation pairs detected in the coincidence experiment appear to originate from markedly excited dication states, not the ground state. We observe 5 two-body dissociations of HCCCN2+, and subsequent decay of one of the ions generated in such two-body processes accounts for the majority of three-body dissociations we observe.

State-selective electron capture in collisions of fully stripped neon ions with ground-state hydrogen

Electron capture and ionisation in bare neon ion collisions with ground-state atomic hydrogen are modelled over the energy range from 1 to 2000 keV/u using the two-center semiclassical wave-packet convergent close-coupling method. The calculated total electron-capture cross section agrees very well with the molecular and atomic orbital close-coupling calculations at low and intermediate energies. Our results slightly overestimate the experimental results by Meyer et al [1985 Phys. Rev. A 32 3310], but underestimate the measurements by Panov et al [1983 Phys. Scr. T3 124] available only below 10 keV/u. At higher energies, where there are no measurements, the results also agree very well with the classical trajectory Monte-Carlo results. Partial n and nl-resolved electron-capture cross sections, important for fusion plasma diagnostics, have also been calculated for final states up to n = 10, where n and l are the final state principal and angular momentum quantum numbers, respectively. The results are generally in good agreement with the atomic calculations. However, due to the finer energy grid used, we are able to detect pronounced oscillations in the state-selective cross sections for n ⩾ 8 at energies below 10 keV/u. Our results for the total ionisation cross section are overall in good agreement with the latest classical trajectory Monte-Carlo results.

Total Ionization Cross Sections due to Electron Impact of Carbon Tetrafluoride from Ionization Threshold to 10 MeV

Modified Khare-BEB model has been used to calculate the electron impact ionization cross section for carbon tetrafluoride (CF4) from ionization threshold to 10 MeV. The collisional parameters CRP and also has been calculated. The calculations are compared with available experimental data . A good agreement is found among the present results, other previous calculations, and experimental data.

Differential Ionization Cross Sections of HCl Molecule

In this article, the differential ionization cross-sections of the HCl molecule in the gas phase is investigated. The single differential ionization cross-section (SDCS) as a function of loss of incident electron energy and Double Differential Cross Section (DDCS) as a function of energy loss of incident electron and incident angle, is calculated. To reach exact values of differential ionization cross sections for HCl molecule, a modified semi-empirical approach of Jain and Khare is used. Partial and total absolute ionization cross-section of HCl is available but there is no data for differential ionization crosssections. So, first time, the results for single and double differential ionization cross-sections for HCl molecule is investigated.

Многолетний тренд реакции Е-слоя ионосферы на солнечные вспышки

Using data from ground-based vertical sounding of the ionosphere (VS) at the station Moscow and five Japanese stations for the period from 1969 to 2015, we have examined the long-term response of the E layer to solar X-ray flares. The analysis relies on the previously developed method for estimating the ratio between rates of ionization by X-rays qx and ultraviolet radiation qu during flares. We confirmed the existence of a long-term (at least covering the 45-year observation period) increase in the proportion of X-rays in the total ionization rate of the ionospheric E layer, characterized by the ratio qx/q, where q=qx+q. The qx/q ratio is shown to increase throughout the period of interest at a rate independent of the solar activity cycle. There is also no dependence of the qx/q trend rate on the season, latitude (26°–56° N), and longitude (37°–28° E).

Long-term trend of the ionospheric E-layer response to solar flares

Using data from ground-based vertical sounding of the ionosphere (VS) at the station Moscow and five Japanese stations for the period from 1969 to 2015, we have examined the long-term response of the E layer to solar X-ray flares. The analysis relies on the previously developed method for estimating the ratio between rates of ionization by X-rays qx and ultraviolet radiation qu during flares. We confirmed the existence of a long-term (at least covering the 45-year observation period) increase in the proportion of X-rays in the total ionization rate of the ionospheric E layer, characterized by the ratio qx/q, where q=qx+q. The qx/q ratio is shown to increase throughout the period of interest at a rate independent of the solar activity cycle. There is also no dependence of the qx/q trend rate on the season, latitude (26°–56° N), and longitude (37°–28° E).

A Theoretical Study of Scattering of Electrons and Positrons by CO2 Molecule

This article presents a theoretical investigation of the differential, integrated, elastic, inelastic, total, momentum-transfer, and viscosity cross-sections, along with the total ionization cross-section, for elastically scattered electrons and positrons from a carbon dioxide (CO2) molecule in the incident energy range of 1 eV ≤Ei≤ 1 MeV. In addition, for the first time, we report the spin polarization of e±−CO2 scattering systems. The independent atom model (IAM) with screening correction (IAMS) using a complex optical potential was employed to solve the Dirac relativistic equation in partial-wave analysis. The comparison of our results with the available experimental data and other theoretical predictions shows a reasonable agreement in the intermediate- and high-energy regions.

Comparison of Total Ionizing Dose Effects in SOI FinFETs Between Room and High Temperature

The synergetic effects of total ionization dose and high-temperature stress of SOI FinFETs are investigated under ON-state bias condition. The experiments and TCAD simulations are employed to analyze the influence of different trapped-charges in the gate and buried oxide on the threshold voltage and mobility variations on the ON-state current of the devices. Results show that the threshold voltage degradation worsens for n-SOI FinFETs but weakens for the p-SOI FinFETs. Also, the ON-state current of n-SOI FinFETs is significantly enhanced while the change of p-SOI FinFETs is weak under the synergetic effects. The threshold voltage degradation induced by synergetic effects for both n- and p-type SOI FinFETs can exceed the linear superposition of the two types of stresses, which may be related to the thermal release of trapped charges in the gate oxide. The enhanced degradation in the n-SOI FinFETs compared with the p-SOI FinFETs may result from the shallow energy level electron traps in HfO2. Besides, for both n- and p-type SOI FinFETs, the ON-state current variations under the synergetic effects depend on the competitive process of threshold voltage variation and the mobility fluctuation.

X-ray irradiation measurements of the radiation tolerance of the ITkPixV1 ATLAS pixel readout chip

The ITkPixV1 chip is the pre-production pixel readout chip for the Phase-2 Upgrade of the ATLAS experiment at the HL-LHC. The harsh environment of HL-LHC, including a peak luminosity of 5 × 1034 cm−1 s−1 and an estimated total ionising dose (TID) of around 1 Grad throughout its lifetime is placing strong requirements on the radiation tolerance of the chip. The radiation tolerance of the ITkPixV1 chip has been tested in irradiation campaigns using X-rays. The digital and analog front-end have been tested up to total doses of 1 Grad (at a dose rate of 4 Mrad/h) and show no significant operational issues.

Effective one-electron approach to proton collisions with molecular hydrogen

The two-centre wave-packet convergent close-coupling approach to ion–atom collisions is extended to study proton collisions with molecular hydrogen including electron-capture channels. We use a model potential to represent the molecular target as an effective one-electron spherically symmetric system. This greatly simplifies the target structure, allowing us to use already existing code developed for ion collisions with single-electron targets. Calculated total cross sections for electron capture, single ionisation, and excitation processes generally agree well with experimental data and other theoretical calculations where available. However, the total electron capture cross section is found to overestimate the experimental data at low energies, while the total ionisation cross section is slightly underestimated. Additionally, we present state-resolved cross sections for capture into the 1s, 2ell , and 3ell states of the projectile where deviation between various previous calculations is substantial. Our results lead to overall improvement over previous theoretical studies although discrepancies with experiment are observed for 3p and 3d capture. We conclude that treating molecular hydrogen as an effective one-electron system within the two-centre coupled-channel approach to one-electron targets can give reasonably accurate total cross sections at intermediate and high energies, without the need for a complex and computationally demanding two-electron target representation.

Fluences of solar energetic particles for last three GLE events: Comparison of different reconstruction methods

Fluxes of solar energetic particles (SEPs), produced and accelerated in and in the vicinity of the Sun, are an important part of cosmic ray induced terrestrial effects such as ionizing radiation on the Earth’s orbit, which affects the exposure to radiation in space as well as the atmospheric ionization. Calculation of these effects requires the knowledge of the integral fluences of SEPs. High-energy solar particles are subject of special interest since they can significantly contribute to the total radiation dose and/or ionization. The main instrument to study the high-energy SEP events is a network of ground-based neutron monitors (NMs), used over the years to register a specific class of SEP, which is called ground-level enhancement (GLE) events. Up today, we possess records from 72 GLE events. Reconstruction of SEP integral and differential fluxes for GLE events using NM data is not an easy task, requires a careful and precise calculation of particle transport in the magnetosphere, atmosphere, and detector itself. In this work, we compare two methods of fluence reconstruction, “fast” and “full”, for the last three registered GLE events and additionally verify one of them using PAMELA experimental data.

Total Electron Detachment and Induced Cationic Fragmentation Cross Sections for Superoxide Anion (O2-) Collisions with Benzene (C6H6) Molecules.

In this study, novel experimental total electron detachment cross sections for O2− collisions with benzene molecules are reported for the impact energy range (10–1000 eV), as measured with a transmission beam apparatus. By analysing the positively charged species produced during the collision events, relative total ionisation cross sections were derived in the incident energy range of 160–900 eV. Relative partial ionisation cross sections for fragments with m/z ≤ 78 u were also given in this energy range. We also confirmed that heavier compounds (m/z > 78 u) formed for impact energies between 550 and 800 eV. In order to further our knowledge about the collision dynamics governing the fragmentation of such heavier molecular compounds, we performed molecular dynamics calculations within the framework of the Density Functional Theory (DFT). These results demonstrated that the fragmentation of these heavier compounds strongly supports the experimental evidence of m/z = 39–42, 50, 60 (u) cations formation, which contributed to the broad local maximum in the total ionisation observed from 550 to 800 eV. This work reveals the reactivity induced by molecular anions colliding with hydrocarbons at high energies, processes that can take place in the interstellar medium under various local conditions.

Status and Extension of the Geant4-DNA Dielectric Models for Application to Electron Transport

The development of accurate physics models that enable track structure simulations of electrons in liquid water medium over a wide energy range, from the eV to the MeV scale, is a subject of continuous efforts due to its importance (among other things) in theoretical studies of radiation quality for application in radiotherapy and radiation protection. A few years ago, the Geant4-DNA very low-energy extension of the Geant4 Monte Carlo code had offered to users an improved set of physics models for discrete electron transport below 10 keV. In this work we present refinements to this model set and its extension to energies up to 1 MeV. Preliminary comparisons against the existing Geant4-DNA physics models with respect to total and differential ionization cross sections of electrons in liquid water are reported and discussed.

A new climatological electron density model for supporting space weather services

The ionosphere is the ionized part of the Earth’s atmosphere, ranging from about 60 km up to several Earth radii, whereas the upper part above about 1000 km height up to the plasmapause is usually called the plasmasphere. We present a new three-dimensional electron density model to support space weather services and mitigate propagation errors for trans-ionospheric signals. The model is developed by superposing the Neustrelitz Plasmasphere Model (NPSM) to an ionosphere model composed of separate F and E-layer distributions. It uses the Neustrelitz TEC model (NTCM), Neustrelitz Peak Density Model (NPDM), and the Neustrelitz Peak Height Model (NPHM) for the total electron content (TEC), peak ionization, and peak height information. These models describe the spatial and temporal variability of the key parameters as a function of local time, geographic/geomagnetic location, solar irradiation, and activity. The model is developed to calculate the electron concentration at any given location and time in the ionosphere for trans-ionospheric applications and named the Neustrelitz Electron Density Model (NEDM2020). A comprehensive validation study is conducted against electron density in-situ data from DMSP and Swarm, Van Allen Probes and ICON missions, and topside TEC data from COSMIC/FORMOSAT-3 mission, bottom side TEC data from TOPEX/Poseidon mission, and ground-based TEC data from International GNSS Service (IGS) covering both high and low solar activity conditions. Additionally, the model performance is compared with the 3D electron density model NeQuick2. Our investigation shows that the NEDM2020 performs better than the NeQuick2 compared with the in-situ data from Van Allen Probes and ICON satellites and TEC data from COSMIC and TOPEX/Poseidon missions. When compared with DMSP and IGS TEC data, both NEDM2020 and NeQuick2 perform very similarly.

Basic features of Ne*-HX (X = Cl, Br) chemi-ionization reactions.

Total and partial ionization cross sections for Ne*(3P2,0)–HX (X = Cl, Br) are presented in a comparative way as a function of the collision energy between 0.02–0.5 eV. New mass spectrometric data on Ne*–HBr chemi-ionization are discussed and analyzed with already published data on Ne*–HCl, highlighting similarities and differences of the collisional stereodynamics of the two systems. Basic features of the interaction potentials, driving reactive collisions, suggest that reaction channels, leading to the formation of parent HX+ ions in the ground and excited electronic state and to the formation of associated NeHX+ ions as well as of NeH+ proton transfer species, are selectively opened within angular cones exhibiting different orientation and acceptance.

Exchange-Correlation Functional Comparison of Electronic Energies in Atoms Using a Grid Basis

Calculation of total energies of the electronic ground states of atoms forms the basis for the frozen-core pseudopotentials used in atomistic calculations of much larger scale. Reference values for these energies provide a benchmark for the validation of new software to calculate such potentials. In addition, basic atomic-scale electronic properties such as the (first) ionization energy provide a simple check on the approximation used in the calculation method. We present a comparison of the total energies and ionization energies of atoms Z = 1 - 92 calculated in density functional theory with several levels of exchange-correlation functional and the Hartree-Fock method, comparing ionization energies to experiment. We also investigate the role of relativistic treatment on these energies.

Ionization cross sections in collisions between two hydrogen atoms by a quasi-classical trajectory Monte Carlo model.

The hydrogen-hydrogen collision system is studied employing a four-body quasi-classical trajectory Monte Carlo model of Kirschbaum and Wilets (QCTMC-KW, C. L. Kirschbaun and L. Wilet, Phys. Rev. A: At., Mol., Opt. Phys., 1980, 21, 834). We present the total ionization cross-section of the target and projectile as a result of pure ionization and electron transfer processes. Calculations were performed in the intermediate energy regime, which is crucial to fusion research. Our results were compared with previous theoretical and experimental results. We found that the quasi-classical approach accurately describes the cross sections of a variety of final channels. We found that the cross-section results by the QCTMC-KW method are higher compared with the standard four-body CTMC results and in good agreement with the experimental data, particularly at low energies.

A binary-encounter-Bethe approach to compute electron-impact partial ionization cross sections of plasma relevant molecules such as hexamethyldisiloxane and silane

Electron-impact partial ionization cross sections (PICS) of fragments are reported from threshold to 5 keV energy using a modified form of the binary-encounter-Bethe model. Scaling using mass spectrometry data ensures that the cross sections are of the correct order of magnitude. The total ionization cross sections (TICS) were obtained by summing the PICS of fragments. The PICS and TICS obtained from the modified-binary-encounter-Bethe model are in excellent agreement with the experimental and theoretical results. The molecules investigated are hexamethyldisiloxane and silane. Both these species are highly relevant in plasma processing where the PICS are required to be over an extended energy range. The study of the ionization process in conjunction with mass spectrometry provides correct estimates of the contribution that each charged ion makes to the TICS. The present approach can be easily extended to any species provided that ion energetics and relative cation abundances data are available.