Projectile Ions Research Articles

Isotopic production cross sections in proton-16O and proton-12C interactions for energies from 10 MeV/u to 100 GeV/u

Proton interactions with16O or 12C nuclei are frequent nuclear interaction leading to secondary radiation in tissues for space radiationandcancer therapy with protons or ion beams. The fragmentation of these ionsby protons produces a large number of heavy ion (A > 4) target or projectile fragments often with high ionization density. Here we develop an analytical model of energy dependent proton-16O and proton-12C cross sections for isotopic nuclei production. Using experimental data and a 2nd order optical modelan accurate formula for the absorption cross section from <10 MeV/u to >10 GeV/u is obtained. The energy dependence of theelemental and isotopiccross sections is modeled as multiplicities scaled toabsorption cross section with average isotopic fractions estimated from experimental data. We show that this approach results in accurateanalytic formulae for isotopic fragmentation cross sections over the full energy range in hadron therapy and space radiation protection studies.

Post collision analyzer to study charge-exchange processes in ion-molecule collisions.

We have designed an electrostatic charge state analyzer for ion beams having energies in the range of 5-20 keV/q. It is primarily built to investigate the different ionization processes involved in the slow (v < 1 a.u.) impact of highly charged ions on molecules. The analyzer is a cylindrical deflector analyzer (CDA) based on a pair of concentric cylindrical sectors of radii 110.2 and 95mm, subtending an angle of 127° at its center. Additionally, an Einzel lens and a quadrupole deflector are deployed to focus and steer the ion beam. The compact design of the analyzer permits easy integration with an ion momentum spectrometer used for studying the fragmentation of the target molecules. The characterization of the CDA including its calibration and its transmission function is carried out using an ion beam delivered from an electron beam ion source. To check the performance of the setup, we have carried out experiments comprising the impact of Ar16+ projectiles on CO2 target molecules at an energy of 18 keV/q. With the help of the CDA, different charge exchange ionization processes, such as single capture, double capture, and triple capture of electrons by the projectile ion have been separated efficiently. The possibility of a modification in the geometry of CDA is discussed to further improve its performance.

Collisions of proton or highly charged ion–atom in a strong magnetic field and dense quantum plasmas

Magneto inertial fusion driven by heavy ions beam (HIB) is a very attractive potential approach for the nuclear energy system. One of the key issues is to investigate the interaction process of the HIB-target considering the condition of plasma screening and strong magnetic field background. In this paper, the influence of the external magnetic field and the plasma screening was investigated by simplifying the process of beam bombarding into a two-body collision between the energetic ions and target atoms. The classical-trajectory Monte Carlo method was accommodated by modifying the Hamiltonian in the collision system, where the effects of plasma screening and the account for the strong magnetic field background were considered. The total cross sections of single electron ionization and charge transfer of the projectile (H+, He2+, Xe32+, Bi31+, U34+)–atom (H, He) collisions are computed. The results indicated that the magnetic field effect becomes more obvious in the low energy regime of the projectiles. With the increase in energy, the change of total cross sections and angular differential cross sections gradually disappears. In the dense quantum plasmas, plasma screening presents very different effects for protons and heavy ion projectiles. This work may pave the way for extending the study to other collision systems calculations.

Channeling electronic stopping power of lithium ions in diamond: Contribution of projectile inner-shell electrons

The electronic energy loss of Li ion in diamond under a channeling condition is studied using real-time time-dependent density functional theory. Simulations with and without inner-shell electrons explicitly considered in describing the electron configuration of projectile Li ions are performed to understand their contribution to the dissipation mechanism. It is found that the explicit involvement of inner-shell electrons is particularly important in describing the charge state of the projectile during collision, especially in the high velocity regime where the inner-shell orbital is indeed far from fully occupied during collision. Due to the overestimate of the electronic screening, Li ions with inner-shell electrons that are frozen show only a reduced and hydrogenlike capability in perturbing the host electronic system.

Model of charge transfer collisions between C60 and slow ions.

A semiclassical model describing the charge transfer collisions of C60 fullerene with different slow ions has been developed to analyze available observations. These data reveal multiple Breit-Wigner-like peaks in the cross sections, with subsequent peaks of reactive cross sections decreasing in magnitude. Calculations of charge transfer probabilities, quasi-resonant cross sections, and cross sections for reactive collisions have been performed using semiempirical interaction potentials between fullerenes and ion projectiles. All computations have been carried out with realistic wave functions for C60's valence electrons derived from the simplified jellium model. The quality of these electron wave functions has been successfully verified by comparing theoretical calculations and experimental data on the small angle cross sections of resonant C60+C60 + collisions. Using the semiempirical potentials to describe resonant scattering phenomena in C60 collisions with ions and Landau-Zener charge transfer theory, we calculated theoretical cross sections for various C60 charge transfer and fragmentation reactions which agree with experiments.

A velocity map imaging spectrometer for measuring absolute differential cross sections for ion-induced electron emission from molecules.

In this paper, we present a newly developed crossed beam experimental setup that utilizes the velocity map imaging (VMI) technique to simultaneously measure both the kinetic energy and emission angle of electrons emitted from atoms or molecules upon ion collision. The projectile ion beam with keV to MeV kinetic energy orthogonally crosses the neutral target beam produced by an effusion cell. The emitted electrons are extracted and analyzed by a multi-electrode VMI spectrometer. By monitoring the target density, the projectile ion beam intensity, and the beams' overlap, we are able to measure absolute differential cross sections for collision-induced electron emission from molecules. The characterization of the setup and the methodology will be presented as well as first results for electron emission from uracil upon 0.98 MeV/u 12C4+ collision.

Emission of x rays in collisions of xenon ions with metal surfaces

X-ray spectra emitted in collisions of 1500 ∼ 3500-keV projectile Xeq+ (q = 12–29) ions with medium-Z Fe, Ni, and Cu targets as well as higher-Z Ta targets are reported. Interestingly, the lines from the collisions with higher-Z targets are mainly composed of characteristic x rays of target atoms, while those from the collisions with medium-Z targets consist mainly of characteristic x rays of projectile ions and broad molecular-orbital x rays. The origins of all these lines and their charge-state dependence are analyzed in detail within the framework of the transient quasi-molecular states which are formed in the collisions. By analyzing the fluorescence yields and vacancy lifetimes of the collision partners, the reasons for the differences in producing x rays between medium-Z and higher-Z targets are discussed in detail for the first time.

State-selective electron capture cross sections in collision between fully striped ions and ground state hydrogen atom—Classical treatment of the collision

We present a state-selective electron capture cross sections database from the ground state hydrogen atom. A standard three-body classical trajectory Monte Carlo (CTMC) and quasi-classical trajectory Monte Carlo (QCTMC) models were employed for impact energies between 10 and 200 keV/amu. The projectile ions are H+, He2+, Li3+, Be4+, B5+, C6+, N7+, and O8+. The cross sections are tabulated for each value of the final quantum numbers n, l, m, summed over m for the given n and l and over l and m for the given n. The maximum quantum number nmax is set to 4 for H+, He2+ and Li3+, as well as to 5 for Be4+, B5+, C6+, N7+ and O8+, respectively.

Dynamic screening and two-center effects in neutral and partially dressed ion-atom collisions

In collisions involving projectiles with bound electrons, partial or total screening of their nuclear charge must be considered. Accordingly, a projectile dynamic effective charge, as a function of the collision momentum transfer, is included in the state-of-the-art continuum distorted wave with eikonal initial state model. This correction, applied in the exit channel, recovers a two-center description from collisions with neutral projectiles. Also, an improvement of both target and projectile ionization double differential cross sections is achieved, especially at the binary encounter and electron capture to the continuum peaks. The results calculated by our analytical model are shown in accordance with previous theoretical and experimental work.

K-shell ionization cross sections of Cu, Zn and Ge by 3–5 MeV/u Si-ion bombardment

The K x-ray spectra of different targets (Cu, Zn, and Ge) induced by 3 to 5 MeV/u Si projectile ions have been measured to determine the K-shell ionization cross-section. A significant difference is observed between the measurements and theoretical estimates, where the theoretical ones are about 28–35% of the experimental results. Such difference is reduced to a good extent 51%–56% if multiple ionization effects are taken into account. Remaining discrepancy may be attributed to the electron capture contribution.

Giant dipole plasmon resonance in fluorene (C13H10) molecules

We report the observation of the giant dipole plasmon resonance in the fluorene molecule $({\mathrm{C}}_{13}{\mathrm{H}}_{10})$, a polycyclic aromatic hydrocarbon, upon collisions with H-like silicon ions. An idea of using highly charged ions to create a large perturbation strength is exploited to observe the plasmon state effectively in the electron double-differential distribution. The signature of plasmon excitation is observed directly as a characteristic broad peak in the electron double-differential spectrum. Such an excited state could not be observed for the same molecule when the low charged ions having lower perturbation were used. This is explained by a model based on dipole approximation and linear response theory for the giant plasmon resonance. The angular distribution of these electrons is modeled using the photoelectron angular distribution for an oscillating dipole superimposed with the postcollision interaction due to the long-range Coulomb interaction between the plasmon electrons and the receding projectile ions.

Lethal DNA damage caused by ion-induced shock waves in cells.

The elucidation of fundamental mechanisms underlying ion-induced radiation damage of biological systems is crucial for advancing radiotherapy with ion beams and for radiation protection in space. The study of ion-induced biodamage using the phenomenon-based multiscale approach (MSA) to the physics of radiation damage with ions has led to the prediction of nanoscale shock waves created by ions in a biological medium at the high linear energy transfer (LET). The high-LET regime corresponds to the keV and higher-energy losses by ions per nanometer, which is typical for ions heavier than carbon at the Bragg peak region in biological media. This paper reveals that the thermomechanical stress of the DNA molecule caused by the ion-induced shock wave becomes the dominant mechanism of complex DNA damage at the high-LET ion irradiation. Damage of the DNA molecule in water caused by a projectile-ion-induced shock wave is studied by means of reactive molecular dynamics simulations. Five projectile ions (carbon, oxygen, silicon, argon, and iron) at the Bragg peak energies are considered. For the chosen segment of the DNA molecule and the collision geometry, the number of DNA strand breaks is evaluated for each projectile ion as a function of the bond dissociation energy and the distance from the ion's path to the DNA strands. Simulations reveal that argon and especially iron ions induce the breakage of multiple bonds in a DNA double convolution containing 20 DNA base pairs. The DNA damage produced in segments of such size leads to complex irreparable lesions in a cell. This makes the shock-wave-induced thermomechanical stress the dominant mechanism of complex DNA damage at the high-LET ion irradiation. A detailed theory for evaluating the DNA damage caused by ions at high-LET is formulated and integrated into the MSA formalism. The theoretical analysis reveals that a single ion hitting a cell nucleus at high-LET is sufficient to produce highly complex, lethal damages to a cell by the shock-wave-induced thermomechanical stress. Accounting for the shock-wave-induced thermomechanical mechanism of DNA damage provides an explanation for the "overkill" effect observed experimentally in the dependence of cell survival probabilities on the radiation dose delivered with iron ions. This important observation provides strong experimental evidence of the ion-induced shock-wave effect and the related mechanism of radiation damage in cells.

Charge‐State Distributions of Highly Charged Lead Ions at Relativistic Collision Energies

AbstractThis study describes the charge‐state evolution of relativistic lead ions passing through a thin aluminum stripper foil. It is motivated by the Gamma Factory project at CERN, where optical laser pulses will be converted into intense gamma‐ray beams with energies up to a few hundred MeV, achieved via excitation of atomic transitions in few‐electron heavy‐ions at highly relativistic velocities. The recently developed BREIT code is employed together with theoretical cross‐sections for single‐electron loss and capture of the projectile ions. All charge‐states starting from Pb54 + up to bare ions are considered at kinetic projectile energies of 4.2 and 5.9 GeV u−1. During recent Gamma Factory beam tests, the calculated preparatory predictions allow to effectively produce Pb80 + and Pb81 + ions from Pb54 + in the transfer beam line between the PS and SPS synchrotron accelerators at CERN and consequently, to store partially stripped ions in the LHC for the very first time. Reasonable agreement is found between the calculations and the very few experimental data available. The study lays the groundwork to optimize the yields of charge states of interest for experiments within the future Gamma Factory project, including the upcoming Gamma Factory Proof‐of‐Principle experiment for which predictions for the production of Pb79 + are presented.

Derivation of an improved semi-empirical expression for the re-ionisation background in low energy ion scattering spectra

Low energy ion scattering is a technique to detect the energy of ions which are scattered from a surface. For noble gas ions, it is predominantly sensitive to the topmost surface layer due to strong neutralisation processes. Depending on the combination of projectile ion and target material, the scattering spectra can exhibit contributions resulting from multiple scattering processes in deeper layers when probing ions are re-ionised on the exiting trajectory. These events cause a pronounced continuum located toward lower scattering energies with respect to the direct scattering peak. In a previous work a semi-empirical formula has been given which allows fitting and derivation of quantitative information from the measured spectra [Nelson 1986 J. Vac Sci. Technol. A 4 1567-1569]. Based on the former work an improved formula is derived which has less numerical artefacts and is numerically more stable.

Measurement of L-shell X-ray production cross sections in 89Y, 158Gd and 209Bi due to 0.3 MeV/u – 1.0 MeV/u 12C ions

Experimental heavy ion induced X–ray production cross sections in matter continue to be of importance for both fundamental ion-atom collision studies as well as practical applications such as in nuclear analytical techniques. This work presents results of L-shell X-ray production cross section measurements in 89Y, 158Gd and 209Bi due to 4 MeV–12 MeV 12Cq + projectile ions. Experimental data are compared with theoretical calculations based on the ECPSSR, ECPSSR + EC and ECPSSR-UA models. Data show fairly good, albeit energy dependent agreement with the different models for yttrium and gadolinium cross sections. For bismuth, all three models overestimate data by an almost constant factor of two. The effect of multiple ionization on the l-line intensity ratios is also presented for gadolinium and bismuth targets.

Significance of the high charge state of projectile ions inside the target and its role in electron capture leading to target-ionization phenomena

The $K$ x-ray spectra of different targets (Cu, Zn, and Ge) induced by 3--5 MeV/u Si projectile ions have been measured to determine the $K$-shell ionization cross section. A significant difference is observed between the measurements and theoretical estimates, with the latter being about 50% below the experimental results. This underestimation is attributed to the charge exchange from the target $K$ shell to projectile $K$ and $L$ shells. Such an observation can only be possible if the projectile ions attain up to H- and He-like charge states. Corresponding projectile charge state fractions have been evaluated from the Lorentzian charge state distribution, where the mean charge state is taken from the Fermi gas model [W. Brandt et al., Phys. Rev. Lett. 30, 358 (1973)] and the width from the Novikov and Teplova approach [Phys. Lett. A 378, 1286 (2014)]. The sum of the direct ionization cross section and $K\text{\ensuremath{-}}K+K\text{\ensuremath{-}}L$ capture cross sections gives a good agreement with the measured cross sections. Furthermore, we have validated this methodology with available data for a Si ion on Ti target. Such results may be useful in many solid target-based applications.

Single and double scattering mechanisms in ionization of helium by electron vortex projectiles

Triple differential cross sections (TDCSs) for electron vortex projectile ionization of helium into the azimuthal plane are calculated using the distorted wave Born approximation. In this collision geometry, the TDCSs at low and intermediate energies exhibit unique qualitative features that can be used to identify single and double scattering mechanisms. In general, our results predict that the ionization dynamics for vortex projectiles are similar to those of their non-vortex counterparts. However, some key differences are observed. For non-vortex projectiles, a double scattering mechanism is required to emit electrons into the azimuthal plane, and this mechanism becomes more important with increasing energy. Our results demonstrate that for vortex projectiles, emission into the azimuthal plane does not require a double scattering mechanism, although this process still significantly influences the shape of the TDCS at higher energies. At low projectile energies, non-vortex ionization proceeds primarily through single binary collisions. The same is generally true for vortex projectiles, although our results indicate that double scattering is also important, even at low energy. Vortex projectiles have an inherent uncertainty in their incident momentum, which causes a broadening of the binary peak at all energies and results in a splitting of the binary peak at higher energies. The results presented here lead to several predictions that can be experimentally tested.

Correct calculation of nitrogen charge state passing through highly ionized carbon plasmas.

In the present work, we reanalyze the energy loss experimental data from Cayzac etal. [Nat. Commun. 8, 15693 (2017)10.1038/ncomms15693] using our successful ion charge state theoretical model. We predict lower nitrogen charge values, from 3.5+ to 5.0+, than the ones calculated by Cayzac etal., fitting better to their data. For energy loss estimations, we use the same stopping model, so our predictions agree better with the experimental data only due to our charge state model. Different projectile electron loss and capture processes are taken into account to estimate the projectile charge state. The projectile electron loss, or ionization, with plasma ions and free electrons are considered. On the other hand, the projectile electron capture, or recombination, with plasma free or bound electrons are also considered. The projectile ionization with plasma ions is shown as the main factor that modifies the mean charge of the projectile. Here, the new Kaganovich fitting formula for this projectile ionization is used because it seems to be more accurate than Gryzinsky's fitting in the low energy range. Our charge state model fits better with experimental data than any other model in the bibliography. Thus, it should be considered in any charge state and any energy loss estimation to obtain reliable results in future work.

Velocity and charge-state dependence on the Coulomb explosion of N2, under the impact of highly-charged ions at intermediate velocities

We report the comprehensive measurement of the Coulomb explosion of the double and triple ionization of N2 in collisions with slow highly-charged ions. The experiments are carried out with ion beams of different charge states for a given velocity (1 a.u.) and at three different velocities for a given charge state (O6+). By analyzing the kinetic energy release distributions of and molecular ions, the effects of projectile velocity and charge state on the population of different molecular states are inferred. We explain such a systematic variation in the population of different molecular states considering the energy deposition to N2 by the projectile ions.

Zinc and copper, by high sensitivity-low energy ion scattering

Low energy ion scattering (LEIS) is an extremely surface sensitive technique that can quantitatively analyze the outermost atomic layer of a material. In LEIS and high sensitivity-low energy ion scattering (HS-LEIS), straightforward quantitation is available using reference and/or standard materials. Here, we present the HS-LEIS spectra of zinc obtained with 3 keV 4He+ and 4 keV 20Ne+ projectile ions. Zinc is an important material with a wide range of applications. Thus, these spectra should be useful standards/references for future applications. A high purity zinc foil was used for these measurements after the removal of the oxide layer. As a reference for the instrumental sensitivity, the spectra for Cu from a high purity foil are also included with this submission. Atomic sensitivity and relative sensitivity factors for Zn and Cu are reported.