Projectile Ions Research Articles

Observation of radiative double electron capture for

Radiative double electron capture (RDEC), occurring when two electrons are captured to a projectile ion with the simultaneous emission of a single photon, has been investigated. RDEC can be considered as the time inverse process of double photoionization. Strong evidence for RDEC is found in F9+ + N2 collisions and additionally for one‐electron F8+ for which the probability for the process is expected to be considerably smaller. Preliminary values for the cross sections for RDEC have been determined. A significant advantage of the gas target is that multiple‐collision effects seen for a solid target are avoided due to the single‐collision conditions that prevail for gas targets.

Argon-seeded plasma exposure and oxidation performance of tungsten-chromium-yttrium smart alloys

Tungsten-chromium-yttrium (WCrY) smart alloys are foreseen as the first wall material for future fusion devices such as Demonstration Power Plant (DEMO). While suppressing W oxidation during accidental conditions, they should behave like pure W during plasma operation due to preferential sputtering of the lighter alloying elements Cr, Y, and W enrichment of the surface. In this paper, the erosion performance of WCrY and W samples simultaneously exposed to deuterium (D) plasma with the addition of 1% of the projectile ions being argon (Ar) ions at an ion energy of 120 eV is compared. With reference to the previous experiments at 120 eV in pure D plasma, the erosion for both WCrY and W is enhanced by a factor of ~ 7. Adding Ar to the D plasma suppresses significant W enrichment previously found for pure D plasma. To investigate the impact of the plasma exposure onto the oxidation performance, plasma-exposed and non-exposed reference samples were oxidised in a dry atmosphere. Results show, on the one hand, that the oxidation suppression of WCrY in comparison to pure W is preserved during the plasma performance. On the other hand, it becomes evident that edge effects imposed by the geometry of the samples used in plasma experiments play a significant role for the oxidation behaviour.

Emission of velocity-correlated clusters in fullerene-solid single collision and diagnostics of the impact energized subsurface nanovolume.

We have measured kinetic energy distributions (KEDs) of large clusters emitted from five different solid targets following a single impact of C60 - ion at 14 keV kinetic energy. It was found that all the large clusters emitted from a given target move with nearly the same velocity and that their KEDs can be described by a thermal distribution riding on a common center-of-mass velocity (shifted Maxwellian) of some precursor. This behavior is in sharp contrast to that observed when the incoming projectile ion is monoatomic. Different trends were observed when comparing the behavior of the KED families of group 5 early transition metal elements (Ta and Nb) with those of group 11 late transition metals (Cu, Ag, and Au). We propose a model for the initial phase of formation of the precursor and show that the measured KEDs can serve as both pressure and temperature probes for the impact excited, highly energized subsurface nanovolume, driving the ejection of the clusters. It is also shown that under the proposed impact scenario, thermally equilibrated conditions (of the atomic subsystem) can be established at the subsurface nanovolume on the early subpicosecond time scale relevant for the emission process. This conclusion is demonstrated both experimentally by the KEDs of the emitted large clusters (very high temperatures and center-of-mass velocity) and by molecular dynamics simulation of the temporal evolution of the thermal characteristics of the impact energized subsurface nanovolume.

State‐selective single‐electron capture in 30‐keV N3+–He collisions

The cold‐target recoil‐ion momentum spectroscopy has been employed to study the single‐electron‐capture processes in collisions of N3+ ions with He atoms at an impact energy of 30 keV. From the longitudinal momentum spectrum of recoil ions, the different electronic configuration was identified, and the metastable projectile ions were distinguished. For the ground‐state N3+(2s2 1S) projectile, the single‐electron capture into the N2+(2s22p 2P) state is the dominant reaction channel, whereas for the metastable‐state N3+(2s2p 3P) projectile, the single‐electron capture into the N2+(2s2p2 2D) state is the main reaction channel. The fraction of the metastable‐state N3+(2s2p 3P) of the incident projectile beam is about 46%. The relative differential cross sections for the capture to different orbitals of N3+ ions are obtained and are compared with other experiments at low energy and the predictions of the classical over‐the‐barrier model.

Two-center interference effects for single electron capture in fast ion-molecule collisions

Total as well as angular-differential cross sections for single electron capture have been investigated in collision of bare ions ($$H^{+}$$, $$He^{2+}$$ and $$Li^{3+}$$) with hydrogen molecules at intermediate and high collision energies with special emphasis on finding interference effects to be exhibited by angular-differential cross sections. Here, we apply the first-order molecular target continuum distorted-wave approximation. Within the distorted-wave formalism, the one-active-electron model, developed to describe collisions with multi-electronic atomic targets, has been employed for the case of $$H_{2}$$ targets. Here, distortion in the final channel related to the Coulomb continuum state of the active electron in the field of residual molecular target ion is included. The present computed results are compared with the available experimental and other theoretical results. The total cross section is obtained by integrating over the projectile’s scattering angle and averaging over all the molecular orientations. The total capture cross sections for all the projectile ions have fair agreement with the experimental observations particularly at lower projectile energies. We have studied the differential cross sections at $$\theta _{\rho }=90^{\circ }$$, $$\phi _{\rho }=0^{\circ }$$, where $$\theta _{\rho }$$ and $$\phi _{\rho }$$ are the polar and azimuthal angles, respectively, of the molecular axis with respect to the incident direction at different impact energies. The interference between two capture amplitudes associated with two centers in the molecule has been found to be more pronounced at fixed orientation of the molecule.

Zero-degree Auger Projectile Electron Spectroscopy of Li-like Ions obtained in Collisions of 1s2s 3S He-like Ions with Gaseous Targets

An experimental station has recently been completed with a beam line dedicated to atomic collision physics at the 5.5 MV TANDEM accelerator laboratory of the Institute of Nuclear and Particle Physics (INPP) at the National Center for Scientific Research (NCSR) “Demokritos” in Athens. A Zero-degree Auger Projectile Spectroscopy (ZAPS) apparatus composed of a single-stage Hemispherical Deflector Analyser (HDA) and a 2-dimensional Position Sensitive Detector (PSD), combined with a doubly differentially pumped gas target has been set up for high resolution studies of electrons emitted from projectile ions at θ = 0◦ with respect to the beam direction in collisions with dilute gas targets. A terminal gas stripper, as well as both a foil and a gas post-stripper, have also been newly installed, enhancing the capabilities of the TANDEM by allowing for the production of more intense, highly charged ion beams, thus complementing and expanding the range of the available energies and charge states of the TANDEM. Using this setup, a systematic isoelectronic investigation of high resolution K-Auger electron spectra emitted from pre-excited ions in collisions with gas targets has been commenced within the APAPES initiative. Here, we present some highlights of this program together with recent results. This investigation is expected to lead to a better understanding of electron capture to excited states of the ion beam and in particular the overlooked role of cascade feeding of metastable states contributing to the capture cross sections, recently a field of contested interpretations awaiting further resolution.

Decomposition of Iron Pentacarbonyl Induced by Singly and Multiply Charged Ions and Implications for Focused Ion Beam-Induced Deposition

Focused ion beams are becoming important tools in nanofabrication. The underlying physical processes in the substrate were already explored for several projectile ions. However, studies of ion inte...

Disentangling the bulk and exit surface contribution on projectile-charge-state evolution

Charge state evolution of the projectile ions while traversing through the solid target medium has been explored using the radiative electron capture process. The measured centroid energies of the convoluted radiative electron capture peak structures have been used to determine the mean K-shell binding energies and mean charge state of the projectile ions. It has been observed that the mean charge states of present measurements are lower than the earlier measurements done using the characteristic ${\mathrm{K}}_{\ensuremath{\alpha}}$ x-ray transitions. The difference is due to the capture of target electrons in the inner-shell vacancies, created during the collision process, of projectile ions. Further, the measured mean charge states are compared with the empirical predictions. A significant discrepancy between experimental and theoretical values has been observed, which is attributed to the multielectron capture by projectile ions due to nonradiative electron capture process from the exit surface while exiting from the foil. The significant variation between mean charge state values obtained from different tools provides a clear indication of the dynamic nature of the charge-changing mechanism at different regions (entrance surface, bulk, and exit surface) of the ion-solid interaction. The present results can be used to validate the departure between the theory and experiment on the charge state dependent stopping powers.

Theoretical investigation of the fully differential cross sections for single ionization of He in collisions with 75-keV protons

We present a theoretical investigation of the single ionization of He in collisions with ${\mathrm{H}}^{+}$ projectile ions at 75-keV impact energy. Using the frameworks of the independent-electron model and the impact parameter picture, fully differential cross sections (FDCS) are evaluated in the continuum distorted-wave with eikonal initial-state approximation (CDW-EIS). Comparisons are made to the recent measurements of Schulz et al. [Phys. Rev. A 73, 062704 (2006)] and Arthanayaka et al. [J. Phys. B: At. Mol. Opt. Phys. 49, 13LT02 (2016)]. Strong influence of the internuclear interaction and effects of target core polarization due to the presence of the projectile ion are observed. Comparing the present results to experimental data and other theoretical predictions, it has been found that the CDW-EIS method qualitatively reproduces structures in the FDCS. Projectile coherence effects are investigated by representing the projectile beam as a Gaussian wave packet. Evidence of interference effects due to projectile-electron and projectile-target core interactions are discussed and the need for further theoretical investigations is proposed.

Release of large polycyclic aromatic hydrocarbons and fullerenes by cosmic rays from interstellar dust

Context. Top-down chemistry is believed to be responsible for the formation of the large molecular compounds such as the polycyclic aromatic hydrocarbon-like molecules and the fullerenes observed in the interstellar medium. The release of these large molecules from the parent grains remains an important issue to be investigated. Aims. Cosmic rays irradiate the dust grains during their journey in the interstellar medium. In this study we probe to what extent electronic sputtering and/or desorption processes induced by high-energy ion projectiles contribute to the creation of the large molecular component in space. Methods. Carbonaceous dust analogues were produced in an ethylene flame. The resulting soot nanoparticles generated under well-defined conditions were irradiated by swift heavy ions, and mass spectra of the ionic and neutral molecular fragments emitted shortly after the impact were monitored. Results. Large molecular fragments were detected, including neutral and ionic polycyclic aromatic hydrocarbons containing up to several tens of carbon atoms, as well as ionic fullerenes. Although the absolute efficiencies were not obtained, these experiments provide a proof of principle of a top-down scenario involving interaction processes of interstellar dust with high-energy projectiles yielding large molecular compounds observed in space.

Spatially resolved magnetic resonance studies of swift heavy ion induced defects and radiolysis products in LiF crystals

Spatially resolved NMR (19F and 7Li) spin–lattice relaxation rates were measured on LiF single crystals irradiated with swift heavy ions of about 10 MeV per nucleon corresponding to several tens of micrometer range. Beyond the ion penetration depth, where the relaxation rate is small enough, also the relaxation dispersion was studied by a spatially resolved mechanical field cycling technique. Experiments were performed on crystals exposed to a variety of beam parameters (ion species, projectile energies and fluences) as well as for varying thermal annealing conditions. In addition to NMR, Q-band EPR was applied to study radiolysis products as produced by annealing. The most important findings are a dose dependent defect region within the ion range and an enhanced relaxation rate beyond the ion range due to characteristic X-ray emission (in case of heavy projectile ions) or nuclear reactions (in case of light projectile ions). Moreover, under certain irradiation conditions molecular fluorine F2 is produced, and thermal annealing involves the formation of metallic lithium, F-center clusters and impurity aggregates.

Процессы захвата и диссоциативного захвата одного электрона при взаимодействии двухзарядных ионов с молекулами CO

AbstractThe absolute cross sections of single-electron capture and single-electron capture with dissociation in the interaction between incident He^2+, C^2+, N^2+, and O^2+ ions with energies from 6.4 to 36.4 keV and СО molecules were measured. It is demonstrated that the cross section of dissociative capture is much larger than the cross section of single-electron capture for O^2+ projectile ions. A qualitative explanation for this effect is provided.

The Comparison of the shares of stopping power in a soft tissue-equivalent material

Introduction: Proton therapy is a type of radiation treatment that it uses protons to treat cancer. Because of the protons’ unique ability to distribute the radiation dose more directly to the tumor, it minimizes the damage to nearby healthy tissues. The rate of energy loss by the ion in the target is called stopping power. The total stopping power is sum nuclear and electronic stopping power. Electronic stopping power refers to the slowing down of a projectile ion due to the inelastic collisions between bound electrons in the medium and the ion moving through it. Nuclear stopping power refers to the elastic collisions between the projectile ion and atoms in the target. Materials and Methods: It should be noted that soft tissue-equivalent material denotes a substance, with absorbing and scattering properties for a given radiation that sufficiently match those of a certain biological tissue. The soft tissue-equivalent material usually consists of four elements of hydrogen, oxygen, carbon and nitrogen. By using the SRIM code, we calculated the total stopping power in each element for 10-MeV proton beam. Then, using Bragg's rule, we got the total stopping power for these elements. Also, using the same code, we obtained the total stopping power for the compound. Also, we obtained the contribution of nuclear and electronic stopping power to the total stopping power in this material. Results: By comparing, we observed that the peak height of stopping power using Bragg's rule is more than 20% higher than the SRIM code. This is due to the core and bond (CAB) corrections at low energies in the SRIM code. Also, we observed that total stopping power is due to the electronic stopping power in high energies. By reducing energy, the electronic stopping power is slowly reduced, and the share of nuclear stopping power slowly increases, and the intersection of these is at 50eV energy. Then the contribution of the nuclear stopping power is greater. Conclusion: The proton therapy to treat cancerous tumors is a major technological advance. In low- energies CAB corrections must be taken into account for stopping power of the compound, and therefore, the peak height of the stopping power is reduced. In soft tissue equivalent material for proton beam the contribution of the nuclear stopping power at energies of less than 50 eV is greater than the electronic stopping power. In other energies, the electron- stopping power share is dominant.

L-shell X-ray production cross sections in metal oxide thin films due to 12C, 16O and 28Si ion beams at MeV SIMS energies

Successful co-implementation of different heavy ion beam nuclear analytical techniques such as heavy ion PIXE, ERDA, MeV SIMS and RBS hinges on the availability of accurate databases of fundamental ion beam-matter interaction parameters. We report on measurements carried out to determine L-shell X-ray production cross sections in 101Ru and 181Ta due to 12C, 16O and 28Si projectile ions in the 0.2 MeV/u–1.0 MeV/u energy range. Experimental data is compared to calculations by one of the most widely implemented X-ray ionisation theories in PIXE analyses – the ECPSSR theory in its modified United Atom (UA) version. Results show fairly good agreement between experiment and theory for the 181Ta target atoms, with the level of agreement improving as the Zion/Ztarget ratio decreases and as beam energy increases. For 101Ru target atoms theoretical predictions tend to underestimate experimental data and the discrepancies increase with projectile mass and decreasing energy. The contribution of projectile electron capture (EC) to the measured X-ray production cross sections is also considered in the data analysis and discussion.

On the Problem of the Ion Energy Loss in Thin Absorbers

Abstract Exact determination of energy loss of ion in materials is still a non-trivial task because of relatively complicated changes of the ion`s stopping power S(E) during transport of the probing ion inside the material structure. Energy loss of ion in the material structure always depends on the current value of continually decreasing energy of the ion, indeed. A purely theoretical approach can be applied to the energy loss calculation in some typical cases. Average energy loss of ion can be determined by means of the Bethe-Bloch analytical theory (1-6) (in high velocity region) and the Lindhard-Scharff-Schiøtt (LSS) theory (7-10) (in low velocity region). Currently, there is no acceptable exact theory to determine the energy loss of ion in intermediate-velocity region (11) and experimental data must be used in that case. Basically, only a finite number of discrete experimental data is always available. Therefore, if the problem how much energy the projectile ion loses in a certain distance travelled is solved, the modelling of function S(E) based on some acceptable assumptions must be applied. In this contribution, we present the energy loss calculations in intermediate-velocity region of ion based on linear interpolation of experimental data. Calculation was carried out for a kapton foil using the data taken from Ziegler, Biersack (12). Energy values of an ion along its trajectory inside the foil were found, and the mean projected range of ion penetrating into the foil was calculated. Finally, the energy resolution was evaluated taking into account straggling provided that the foil is used as an absorber in the ERDA experiment.

USNA Pelletron accelerator applications with heavy ion projectiles

Abstract Tandem particle accelerators produce beams of atomic nuclei which are used for nuclear physics or materials science experiments. The U.S. Naval Academy tandem has predominately been used only for proton beams during the past 27 years. This project developed beams of projectiles more massive than helium for the first time and used them for materials science applications. Special scattering chambers were developed for ion implantation and the study of scintillating materials.

Electronic stopping power from time-dependent density-functional theory in Gaussian basis

The electronic stopping power, which is the energy transfer from a charged particle travelling through a material to the electrons of the material, has attracted much attention back from the early beginnings of quantum mechanics. It requires the description of the electronic excitations taking place in the target material and has been limited to model systems for a long time. With the advent of time-dependent density-functional theory (TDDFT), it is nowadays possible to provide a complete and realistic quantum-mechanical description of the phenomenon. We present here an implementation of TDDFT based on Gaussian basis for finite systems. The localized Gaussian basis has numerous advantages, such as the cheap account of core electrons, the simple implementation of the modern hybrid functionals, and the possibility of a tunable basis accuracy as a function of space. With our tool, we explore the bulk limit, the validity of the impact parameter averaging to obtain the experimental random electronic stopping power, and the connection to the simpler linear-response results for lithium metallic clusters for different ionic projectiles.

Enhancement of Intact Ion Yields in ToF-SIMS Using Molecular Cluster Ion Beams

Recently, water and some other molecules are applied to the massive cluster projectiles for SIMS to improve the secondary ion yields by chemical effects. The ionization probability should be influenced by the properties of the primary ion beams as well as the chemical nature of the sample surface. However, the mechanisms of ionization by the large cluster collision is still unclear. In this study, we have generated water, methanol and methane molecular cluster ion beams and investigated the secondary ion emission from amino acid thin films bombarded by the molecular cluster ion projectiles.

Solar wind sputtering of wollastonite as a lunar analogue material – Comparisons between experiments and simulations

The sputtering of wollastonite (CaSiO3) by solar wind-relevant ions has been investigated experimentally and the results are compared to the binary collision approximation (BCA) codes SDTrimSP and SRIM-2013. Absolute sputtering yields are presented for Ar projectiles as a function of ion impact energy, charge state and impact angle as well as for solar wind H projectiles as a function of impact angle. Erosion of wollastonite by singly charged Ar ions is dominated by kinetic sputtering. The absolute magnitude of the sputtering yield and its dependence on the projectile impact angle can be well described by SDTrimSP as long as the actual sample composition is used in the simulation. SRIM-2013 largely overestimates the yield especially at grazing impact angles. For higher Ar charge states, the measured yield is strongly enhanced due to potential sputtering. Sputtering yields under solar wind-relevant H+ bombardment are smaller by two orders of magnitude compared to Ar. Our experimental yields also show a less pronounced angular dependence than predicted by both BCA programs, probably due to H implantation in the sample. Based on our experimental findings and extrapolations to other solar wind ions by using SDTrimSP, we present a model for the complete solar wind sputtering of a flat wollastonite surface as a function of projectile ion impact angle, which predicts a sputtering yield of 1.29 atomic mass units per solar wind ion for normal impact. We find that mostly He and some heavier ions increase the sputtering yield by more than a factor of two as compared to bombardment with only H+ ions.

Double Charge Exchange Reactions and Double Beta Decay

The subject of this presentation is at the forefront of nuclear physics, namely double beta decay. In particular one is most interested in the neutrinoless process of double beta decay, when the decay proceeds without the emission of two neutrinos. The observation of such decay would mean that the lepton conservation symmetry is violated and that the neutrinos are of Majorana type, meaning that they are their own anti-particles. The life time of this process has two unknowns, the mass of the neutrino and the nuclear matrix element. Determining the nuclear matrix element and knowing the cross-section well will set limits on the neutrino mass. There is a concentrated effort among the nuclear physics community to calculate this matrix element. Usually these matrix elements are a very small part of the total strength of the transition operators involved in the process. There is no simple way to “calibrate” the nuclear double beta decay matrix element. The double beta decay is a double charge exchange process, therefore it is proposed that double charge exchange reactions using ion projectiles on nuclei that are candidates for double beta decay, will provide additional necessary information about the nuclear matrix elements.