Projectile Ions Research Articles

Experimental subshell vacancies in a multiply ionised Sn atom by heavy ion impact

The adoption of Heavy Ion PIXE for elemental quantification remains limited by the lack of fundamental atomic parameters needed for the calculation of X-ray production cross section data. Widely adapted theoretical models used for approximating ionisation cross sections, as well as other atomic physical parameters such as X-ray fluorescence yields, are calculated based on single-hole vacancy production post ion-atom impact. This renders the use of conventional ‘protonic’ models invalid for heavy ion-atom collisions. The degree to which Multiple Ionisation (MI) manifests in different heavy ion-atom collision symmetries significantly modifies atomic physical parameters. This is due to the significant number of introduced spectator vacancies in higher subshells, especially where near-symmetry is approached and MI is more pronounced. Knowledge of the mean number of vacancies in upper subshells is thus important for modifying atomic parameters that are needed for the translation of ionisation to X-ray production cross sections. In the present study, MI effects for Sn L-shell X-rays were studied using characteristic X-ray energy shifts measured using a standard PIXE spectrometer induced by Si, Cu and I projectile ions with incident energies up to 0.75 MeV/u. MI satellite distributions were studied using a Wavelength dispersive X-ray spectrometer (WDS) for high resolution PIXE, induced by C and Si projectile ions with incident ion energies up to 1.25 MeV/u. The mean number of subshell vacancies in the M- and N- shell for energy shifted Sn Lα X-ray lines were determined using both standard and high resolution PIXE spectrometers.

Coulomb excitation of hydrogen atoms by vortex ion beams

Abstract Coulomb excitation of hydrogen atoms by vortex protons is theoretically investigated within the framework of the non--relativistic first--Born approximation and the density matrix approach. Special attention is paid to the magnetic sublevel population of excited atoms and, consequently, to the angular distribution of the fluorescence radiation. We argue that both these properties are sensitive to the projection of the orbital angular momentum (OAM), carried by the projectile ions. In order to illustrate the OAM--effect, detailed calculations have been performed for the $1s \to 2p$ excitation and the subsequent $2p \to 1s$ radiative decay of a hydrogen target, interacting with incident Laguerre--Gaussian vortex protons. The calculation results suggest that Coulomb excitation can be employed for the diagnostics of vortex ion beam at accelerator and storage ring facilities.

A review of ion scattering spectroscopy studies at liquid interfaces with noble gas ion projectiles

Ion scattering spectroscopy (ISS) is an analytical tool that provides direct structural, topographical, and atomic compositional information at interfaces when ions are used as projectiles. Since its development in 1967, ISS is commonly used to obtain quantitative information about solid interfaces. Over the last couple of decades, ISS has emerged as an important technique to probe liquid interfaces and their studies employing ISS has become not uncommon, more so with Neutral impact collision ion scattering spectroscopy (NICISS). Therefore, here the principle of ISS with a particular focus on NICISS and its data evaluation are summarised while reviewing some important studies at vapor-liquid interfaces that provide direct information for molecular orientation of liquids (including ionic liquids), composition and distribution of atoms (or solutes) and charges as a function of depth to gain vast variety of thermodynamical information. Employing ISS such information can be achieved with high depth resolution of ∼1–2 Å (depending on the nature of the experiment). These examples highlight the significance of ISS and show potential for its application for studies related to specific ion effects, atmospheric reaction in aerosol and sea water droplets, and even determining the fate of environmental pollutants like heavy metal ions and per-fluoroalkyl substances (PFAS). Furthermore, some limitations of ISS are also discussed relating to investigation of high-vapor pressure liquids and probing buried interfaces like liquid-liquid interfaces while presenting progresses made in probing solid-liquid interfaces.

Multiple differential electron spectra from detachment in collisions of 30–300-keV anions with atoms and molecules

We have measured triple differential momentum distributions for electron detachment in collisions of 30- and 300-keV anions (C− and Si−) with atoms and molecules (He, Ar, and N2). The entire angular range of the ejected electrons was covered. The binary encounter ring, well known from positive ion-atom collisions, was observed in most cases. In a quasifree-electron scattering model this structure represents elastic scattering of the active electron from the target. However, especially for the slowest projectiles, this model fails to reproduce the angular distributions. In this regime it is probably necessary to use quasimolecular models to describe the collision. Indications for a projectile cusp are observed, implying that excitation-induced dipole moments in the ion projectile may be important. Published by the American Physical Society 2024

State-selective electron capture in Ar16++H(1s) collisions for charge-exchange recombination spectroscopy

Abstract State-selective electron capture in collisions of Ar16+ ions with ground-state hydrogen atoms has been modeled using the two-center wave-packet convergent close-coupling approach. The partially stripped He-like projectile ion is represented using a model potential. Experimental measurements are not available for this collision system and to date, only the classical trajectory Monte Carlo (CTMC) method has been applied to calculate cross sections. The calculated total electron-capture cross section (TECS) is in good agreement with the previous CTMC results at the low energies but slightly larger at higher energies. This is likely because, in this work, we account for capture into highly excited states, which contribute significantly to the TECS at the intermediate energies. The n-resolved electron-capture cross sections have also been presented for capture into states with n = 6 − 19 , where n is the final-state principal quantum number. The most important of these are the cross sections for capture into the n = 14 − 17 states, which are used in charge-exchange recombination spectroscopy techniques. For these cross sections, a significant difference is observed between the present and previously published data. The cross sections differ by an order of magnitude in the 10−60 keV u−1 energy range. The agreement between the calculations is observed at the energies above 70 keV u−1. The n ℓ -resolved electron-capture cross sections have also been presented at 15, 60, 100 and 200 keV u−1 projectile energies, where ℓ is the final-state angular momentum quantum number.

Contribution of different electron-capture mechanisms in the fragmentation of CO23+ upon slow ion-molecule collision

Abstract We present recoil ion - projectile ion coincidence study on the three body fragmentation of CO23+ ion into C+ + O+ + O+ fragments upon impact with
Ar3+, Ar6+ and Ar8+ projectile ions having the same velocity of vp = 0.49 a.u. (atomic units) using recoil ion momentum imaging technique. The kinetic energy
release (KER) distributions are presented and effect of different electron-capture associated processes such as pure capture, electron capture followed by target ionization or projectile auto-ionization is discussed based on the analysis of KER corresponding to different final projectile charge state post collision. As the capture stabilization increased the relative yields in the KER distribution are found to decrease in the high KER side for low charged Ar3+ impact, while an increase is observed for Ar6+ and Ar8+ impacts. We discussed the interplay between electron-capture, projectile auto-ionization and target ionization for the dominance of particular process. We also observed a low-KER feature around 15 eV which was observed for electron
and proton impacts, which was not yet observed for highly charged ion impacts

The n-resolved single-electron capture in slow O6+–Ne collisions

Abstract A study of single-electron capture (SEC) in 18–240 keV O6+–Ne collisions has been conducted employing a combination of experimental and theoretical methodologies. Utilizing a reaction microscope, state-selective SEC cross sections and projectile scattering angle distributions were obtained. The translational energy spectra for SEC reveal the prevailing capture into n = 3 states of the projectile ion, with a minor contribution from n = 4 states. Notably, as the projectile’s energy increases, the relative contribution of SEC n = 4 states increases while that of SEC n = 3 states diminishes. Furthermore, we computed state-selective relative cross sections and angular differential cross sections employing the classical molecular Coulomb over-the-barrier model (MCBM) and the multichannel Landau–Zener (MCLZ) model. A discernible discrepancy between the state-selective cross sections from the two theoretical models is apparent for the considered impact energies. However, regarding the angular differential cross sections, an overall agreement was attained between the current experimental results and the theoretical results from the MCLZ model.

Correlated ion stopping in dense plasmas with a temperature‐dependent plasmon pole approximation

AbstractThe plasmon pole approximation used for the stopping function in a dense electron plasma is given a temperature‐dependent cutoff wavenumber via the ion projectile thermal wavelength. Excepted for projectile inter‐ion distance smaller than the target electron screening length and small ion fragment velocities, featuring a attosecond interaction time with a maximum correlated ion stopping (CIS) in inertial confinement fusion and warm dense matter (WDM), the given procedure is shown to yield back accurately the CIS estimated within the standard random phase approximation framework at any temperature, provided the ion fragment distribution is taken Gaussian.

ERCS24: An updated version of the ERCS08 program for calculations of the cross sections for atomic electron removal based on the ECPSSR theory and its variants

ERCS24: An updated version of the ERCS08 program for calculations of the cross sections for atomic electron removal based on the ECPSSR theory and its variants

Increasing the rate capability for the cryogenic stopping cell of the FRS Ion Catcher

At the FRS Ion Catcher (FRS-IC), projectile and fission fragments are produced at relativistic energies, separated in-flight, energy-bunched, slowed down, and thermalized in the ultra-pure helium gas-filled cryogenic stopping cell (CSC). Thermalized nuclei are extracted from the CSC using a combination of DC and RF electric fields and gas flow. This CSC also serves as the prototype for the CSC of the Super-FRS, where exotic nuclei will be produced at unprecedented rates making it possible to go towards the extremes of the nuclear chart. Therefore, it is essential to efficiently extract thermalized exotic nuclei from the CSC under high beam rate conditions, in order to use the rare exotic nuclei, which come as cocktail beams. The dependence of the extraction efficiency on the intensity of the impinging beam into the CSC was studied with a primary beam of 238U and its fragments. Tests were done with two different versions of the DC electrode structure inside the cryogenic chamber, the standard 1 m long and a short 0.5 m long DC electrode systems. In contrast to the rate capability of 104 ions/s with the long DC electrode system, results show no extraction efficiency loss up to the rate of 2 × 105 ions/s with the new short DC electrode. This order of magnitude increase of the rate capability paves the way for new experiments at the FRS-IC, including studies of exotic nuclei with in-cell multi-nucleon transfer reactions. The results further validate the design concept of the CSC of the Super-FRS, which was developed to effectively manage beams of even higher intensities.

Ionization of CH[formula omitted] under fast He-like Si-ion impact

We have studied the absolute double differential cross section (DDCS) of electrons ejected from the methane molecule (CH4) under the impact of highly charged fast projectile ions. The energy and angular distributions of electrons have been measured in interactions with 70 MeV Si12+ ions. These DDCS data together with the derived single differential cross sections and the total cross section (TCS) have been compared with predictions of the continuum distorted wave-eikonal initial state model using different approaches for the molecular orbitals. It has been found that the theories overestimate the measured DDCS values at low ejection energies, which may indicate shortcomings of the model in the case of strong perturbation. At the same time, applying the model to a previous measurement using fast C ions having a lower perturbation strength, excellent agreements have been obtained with the experimental data. Considering the scaling properties, the available TCS data have been plotted with a scaled parameter, namely the perturbation strength, q/v (where q= charge state, v=velocity of the projectile). The KLL Auger e-emission as well as the KLL hyper-satellite peaks are analyzed for different emission angles. The double K-vacancy production shows a considerable enhancement i.e. 37% of the single production cross section which is consistent with some of the recent experiments on K-ionization using x-ray techniques.

Efficiency and resolution characterisation of a high-resolution bent crystal X-ray spectrometer using ray-tracing simulations

We report the characterisation of the efficiency and resolution of a high-resolution bent crystal spectrometer under Johannson geometry, using ray-tracing simulations. The spectral resolution is measured experimentally from electron-beam and fast ion-beam interactions with thin solid foils. The X-rays emitted by target atoms as well as projectile ions are studied. The results of the ray-tracing simulations are in very good agreement with the beam-foil spectroscopy experiments. The geometrical factors affecting the resolution are also discussed in detail. We also characterise the detection efficiency of the spectrometer by simultaneous measurements of X-rays using a semiconductor detector, i.e. Si(Li) detector, with known detection efficiency. These results are also compared with the ray-tracing simulation results.

Single-electron-capture from helium by projectile ions in intermediate-to-high energies

Single-electron-capture from helium by projectile ions in intermediate-to-high energies

Impact ionization of highly charged ion-atom collisions considering strong magnetic field and plasma screening effect

The impact ionization process of target is a crucial issue in the study of Heavy Ion Beam (HIB)-driven Magnetized Inertial Fusion (MIF). The collision systems between heavy projectile ions (Xeq+, Biq+, Uq+) and light target atoms/ions (H, D, T, 3He, 3He+, 11B) are promising candidate reactions for fusion power. In this study, the impact ionization process in medium-energy (ranges 1–100 MeV/u) is studied numerically based on the extended Classical-trajectory Monte Carlo (CTMC) method, where the effects of projectile charge state, external magnetic field and plasma screening on the single ionization process are considered. The results show that the existed external magnetic field results in a decrease of the yield of ionized high-energy electrons, whereas the yield of backward emitted electrons is increased. The effect of plasma screening on the ionization process is shown to be determined by the competition between the screening charge of projectile ion and the target nucleus. Thus, a significant decrease of ionization cross section is found in the low energy region since the screening charge of projectile ion is dominant. However, the screening effect of target nucleus charge is dominant in high energy region, where a significant increase of ionization cross sections is found.

Projectile Coherence Effects in Twisted Electron Ionization of Helium

Over the last decade, it has become clear that for heavy ion projectiles, the projectile’s transverse coherence length must be considered in theoretical models. While traditional scattering theory often assumes that the projectile has an infinite coherence length, many studies have demonstrated that the effect of projectile coherence cannot be ignored, even when the projectile-target interaction is within the perturbative regime. This has led to a surge in studies that examine the effects of the projectile’s coherence length. Heavy-ion collisions are particularly well-suited to this because the projectile’s momentum can be large, leading to a small deBroglie wavelength. In contrast, electron projectiles that have larger deBroglie wavelengths and coherence effects can usually be safely ignored. However, the recent demonstration of sculpted electron wave packets opens the door to studying projectile coherence effects in electron-impact collisions. We report here theoretical triple differential cross-sections (TDCSs) for the electron-impact ionization of helium using Bessel and Laguerre-Gauss projectiles. We show that the projectile’s transverse coherence length affects the shape and magnitude of the TDCSs and that the atomic target’s position within the projectile beam plays a significant role in the probability of ionization. We also demonstrate that projectiles with large coherence lengths result in cross-sections that more closely resemble their fully coherent counterparts.

Electron Emission Cross Section from Methane under 250 keV Proton Impact

We measure double differential cross sections (DDCS) of electrons emitted from CH4 molecules in collisions with 250 keV protons. The projectile ions are obtained from a 400 kV electron cyclotron resonance-based ion accelerator (ECRIA). We study the energy and angular distributions of the electron DDCS. The observed double and single differential and the total cross section are compared with the state-of-the-art continuum distorted wave eikonal initial state (CDW-EIS) model predictions. Two different approaches are used considering the different target descriptions: complete neglect of differential overlap (CNDO) and molecular orbital (MO) approximations. The MO model uses two different scaling parameters (d = 0.7 and 1.0). In the energy distribution of the DDCS, the carbon KLL Auger line is also observed at 240 eV. The single differential cross section (SDCS) and total cross section (TCS) are derived. Both the MO-based CDW-EIS models are in good agreement with the experimental results; however, the CNDO approach overestimates the data.

3D Potential Simulation for H2+ ion Under a Strong Laser Field

Potential is the most important quantity needed to be concerned in the study of interaction between projectile ion and target. On the one hand, it decides the total interaction course such as ion energy deposition and molecular Coulomb explosion and so on. On the other hand, under a strong laser field, the potential can be influenced by the laser. In this paper, the 3D potential is studied under a strong laser field for a hydrogen molecular ion in Al target. The simulation results show that the 3D potential is weakened by the laser intensity. Such results can provide references for correlated experiments and theoretical study.

Surface characterization of CaF2 crystals irradiated with MeV ions below charge state equilibrium

Single crystals of CaF2, cleaved along the (111) plane, were irradiated by 35Cl, 39K, 52Cr, 58Ni, 79Br and 197Au ions with energies from 2 to 48 MeV, charge states from 1+ to 11+ and ion fluences from 2 × 1010 to 1 × 1013 ions/cm2. The surface properties of the irradiated samples were studied using Atomic Force Microscopy in contact mode. Nanoscale surface structures were observed for some surfaces irradiated by Cl, K, Cr, Ni, Br and Au ions. Thresholds for nanostructure formation were found in terms of projectile ion velocity and electronic stopping power (Se). Clear surface modification was observed for projectiles with specific energies above approximately 0.04 MeV/u. The threshold in Se for the generation of distinct triangular structures was observed to be velocity-dependent. The average formation efficiency, referring to the ratio of the number of distinct nanostructures observed on the surface to the number of incident ions, as well as the average height of nanostructures increases with Se.

Effects of semicore electrons on stopping power in helium-irradiated aluminum nanosheets.

The stopping power of energetic He ions traversing an Al film is studied by combining the time-dependent density-functional theory method with molecular dynamics simulations. We investigated the dependence of the semicore electron excitation of the Al film on the projectile's trajectory and its charge state. Our results show that for the off-channeling trajectories the semicore electrons contribute significantly to the stopping power of the Al film as the He+ ion velocity exceeds 1.0 a.u, and in contrast, it is negligible for the channeling trajectories. Most importantly, we found two unexpected effects of semicore electrons on the stopping power in helium-irradiated aluminum nanosheets, i.e., (1) the semicore electrons can contribute to the energy loss for both high and low energy projectiles under the off-channeling trajectory; (2) as the projectile velocity increases from 0.4 a.u. to 2.0 a.u. although semicore electron excitation (including transition in the target, ionization away from the target and transfer to the projectile ion) of the target atom is gradually inhibited, the influence of semicore electrons on valence electron excitation is gradually enhanced. Our finding allows us to gain new insights into the stopping of ions in metals.

Energy-loss enhancement and charge-equilibration time for highly charged xenon ions at near-Bohr velocity in solids

We probe the energy-loss enhancement in preequilibration and the charge-equilibration time for highly charged Xe ions $({q}_{\mathrm{in}}=15--26)$ at near-Bohr velocity impinging on an Al target by measuring the dependence of the Xe $L$-shell x-ray yield on the initial charge state of the ions. The present results are found to be very consistent with those obtained in ion-transmission thin-foil experiments. The charge-equilibrium time is measured in the near-Bohr velocity region of highly charged ions in solids. Moreover, for the present collision system it is demonstrated by measuring the inner-shell x rays that the ionization of the inner-shell electrons of the projectile ions starts to contribute to ion energy loss at near-Bohr velocity.