Charge Exchange Cross Sections Research Articles

Observation of large enhancements of charge exchange cross sections with neutron-rich carbon isotopes

Production cross sections of nitrogen isotopes from high-energy (∼950 MeV per nucleon) carbon isotopes on hydrogen and carbon targets have been measured for the first time for a wide range of isotopes (A = 12 to 19). The fragment separator FRS at GSI was used to deliver C-isotope beams. The cross sections of the production of N-isotopes were determined by charge measurements of forward-going fragments. The cross sections show a rapid increase with the number of neutrons in the projectile. Since the production of nitrogen is mostly due to charge-exchange (Cex) reactions below the proton separation energies, the present data suggests a concentration of Gamow-Teller and/or Fermi transition strength at low excitation energies for neutron-rich carbon isotopes. It was also observed that the Cex cross sections were enhanced much more strongly for neutron-rich isotopes in the C-target data.

Equilibrium thickness of carbon target interacting with nitrogen and neon ion beams

The method for calculation of the target thickness which is required for the formation of equilibrium charge distribution of ions is proposed. The description of nonequilibrium processes is based on empirical estimations of charge-exchange cross sections, taking the density effect for solids into account. The variation of the average charge and the width of the nonequilibrium charge distribution as a function of the target thickness is analyzed. The results of calculations for nitrogen and neon ions in carbon are compared with experimental data.

Charge-exchange processes in collisions ofH+,H2+,H3+,He+, andHe2+ions with CO andCO2molecules at energies below 1000 eV

Absolute measurements of charge-exchange cross sections of ${\mathrm{H}}^{+},\phantom{\rule{0.16em}{0ex}}{\mathrm{H}}_{2}^{+},\phantom{\rule{0.16em}{0ex}}{\mathrm{H}}_{3}^{+},\phantom{\rule{0.16em}{0ex}}{\mathrm{He}}^{+}$, and ${\mathrm{He}}_{2}^{+}$ ions in CO and ${\mathrm{CO}}_{2}$ have been made for energies below 1000 eV, an equivalent of the energy of ionized particles at typical solar-wind conditions. An attenuation method for the case of complex ions of a molecule, taking into account the influence on the ion beam composition of the processes of disintegration of the primary ions into secondary ones with different charge-exchange cross sections, is described. Also the secondary effects, like three-body collisions and re-ionization processes that could emerge at higher pressures of the gas layer, are discussed. Dependence of the cross sections on the number of atomic centers in the projectile have been explained on the basis of the energy defect of the reactions and asymmetric near-resonant charge-exchange process between the ion and target molecule including the Doppler broadening in the interaction of the monoenergetic ion beam and target molecules having an isotropic Maxwellian velocity distribution corresponding to room temperature. Using the semiempirical approach based on the parametrized numerical coupled-channel two-state calculations, we have extrapolated the cross sections to a broader range of velocities.

Single electron capture cross sections for protons colliding with neon and methane targets: effects of the initial vibrational state of CH4

The process of neutralization of ions induced by collisions is crucial to understanding the chemical evolution of interstellar gas. However, the role of the initial vibrational state of the target molecule is not completely understood. In this work, we carry out a combined experimental and theoretical study of the vibrational target effects on the single electron charge exchange cross sections for protons colliding with CH4 in the keV energy region. We complement our study by analyzing the single electron capture from the iso-electronic neon atom to discern similarities and differences. For our experimental study, we use the growth-rate method for the determination of the single electron capture cross section on both systems. For the theoretical study, we use an electron–nuclear dynamics approach for the time evolution of the system wave function to find out the final projectile charge state. We report charge exchange probabilities and cross sections for H+ projectiles when colliding on both targets. We find that these ten-electron systems would have an asymptotically similar charge exchange cross section at high collision energies and would differentiate in the intermediate to low collision energies due to the energetics of the valence electrons and initial vibrational state. In the case of the protons colliding with CH4, we find that it is easier to capture an electron from a CH4 target than from the Ne. Furthermore, we find that low vibrational states have a higher contribution to the electron capture cross section as the collision energy is reduced. We stress the importance of taking into account the initial bending and stretching vibrational modes in the study of the electron capture process. For the neon target, the high ionization potential of the valence electrons produces a smaller charge exchange cross section for low proton collision energies when compared to the CH4 target. We report good comparison to available experimental data. We expect our findings to encourage further theoretical and experimental study of initial vibrational effects at low collision energies to understand the chemical evolution of neutralization processes.

Inelastic processes inNa+-Ne,Na+-Ar,Ne+-Na, andAr+-Na collisions in the energy range 0.5–14 keV

Absolute cross sections for charge-exchange, ionization and excitation in Na$% ^{+}-$Ne and Na$^{+}-$Ar collisions were measured in the ion energy range $% 0.5-10$ keV using a refined version of a capacitor method, and collision and optical spectroscopy methods simultaneously in the same experimental set-up. Ionization cross sections for Ne$^{+}-$Na and Ar$^{+}-$Na collisions are measured at the energies of $2-14$ keV using a crossed-beam spectroscopy method. The experimental data and the schematic correlation diagrams are used to analyze and determine the mechanisms for these processes. For the charge-exchange process in Na$^{+}$ $-$Ar collisions two nonadiabatic regions are revealed and mechanisms responsible for these regions are explained. Structural peculiarity on the excitation function for the resonance lines of argon atoms in Na$^{+}$ $-$Ar collisions are observed and the possible mechanisms of this phenomenon are explored. The measured ionization cross sections for Na$^{+}-$Ne and Ne$^{+}-$Na collisions in conjunction with the Landau-Zener formula are used to determine the coupling matrix element and transition probability in a region of pseudo-crossing of the potential curves.

Strong sensitivity of x-ray emission lines following charge exchange between highly charged ions andH(1s)in weakly screened media

Fil: Cariatore, Nelson Daniel. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Bahia Blanca. Instituto de Fisica del Sur. Universidad Nacional del Sur. Departamento de Fisica. Instituto de Fisica del Sur; Argentina

Heavy-ion double charge exchange reactions: A tool toward $0 \nu\beta\beta$ nuclear matrix elements

The knowledge of the nuclear matrix elements for the neutrinoless double beta decay is fundamental for neutrino physics. In this paper, an innovative technique to extract information on the nuclear matrix elements by measuring the cross section of a double charge exchange nuclear reaction is proposed. The basic point is that the initial and final state wave functions in the two processes are the same and the transition operators are similar. The double charge exchange cross sections can be factorized in a nuclear structure term containing the matrix elements and a nuclear reaction factor. First pioneering experimental results for the 40Ca(18O,18Ne)40Ar reaction at 270 MeV incident energy show that such cross section factorization reasonably holds for the crucial 0+ --> 0+ transition to 40Args, at least at very forward angles.

The RHIC polarized H⁻ ion source.

A novel polarization technique had been successfully implemented for the Relativistic Heavy Ion Collider (RHIC) polarized H(-) ion source upgrade to higher intensity and polarization. In this technique, a proton beam inside the high magnetic field solenoid is produced by ionization of the atomic hydrogen beam (from external source) in the He-gaseous ionizer cell. Further proton polarization is produced in the process of polarized electron capture from the optically pumped Rb vapor. The use of high-brightness primary beam and large cross sections of charge-exchange cross sections resulted in production of high intensity H(-) ion beam of 85% polarization. The source very reliably delivered polarized beam in the RHIC Run-2013 and Run-2015. High beam current, brightness, and polarization resulted in 75% polarization at 23 GeV out of Alternating Gradient Synchrotron (AGS) and 60%-65% beam polarization at 100-250 GeV colliding beams in RHIC.

Scaling for state-selective charge exchange due to collisions of multicharged ions with hydrogen

In this article we evaluate state-resolved charge exchange cross sections for Be and projectiles colliding with atomic hydrogen employing two different methods: the classical trajectory Monte Carlo and the eikonal impulse approximations. These cross sections are used to extend previously derived scaling laws for n-, nl-, and nlm-distributions to highly excited final levels with covering energies in the range amu. Present total and partial capture cross sections are in agreement with available experimental and theoretical data for these collision systems. Besides, the proposed scaling rules are also verified by other theories, becoming a useful instrument for plasma research.

Population distribution subsequent to charge exchange of 29.85 keV Ni+ on sodium vapor

The population of low-energy metastable states in Ni I subsequent to charge-exchange reactions and cascade decay was studied for 29.85keV Ni ions impinging on a sodium vapor. The charge-exchange cross sections were calculated using a semi-classic time-dependent perturbation theory and redistribution of the population via rapid spontaneous decays was simulated. Collinear laser spectroscopy experiments were performed on four emission lines in Ni I to determine populations in low-energy metastable states: 3d94s3D3 (204.787cm−1), 3d94s3D2 (879.816cm−1), 3d94s3D1 (1713.087cm−1) and 3d94s1D2 (3409.937cm−1). Fair agreement was obtained between the simulation and experimental results. The low-energy metastable states were preferentially populated after the cascade decay in contrast to weak populations in near-resonant high-energy states in Ni I.

Scaling for state-selective charge exchange due to collisions of multicharged ions with hydrogen

SynopsisState-resolved charge exchange (CX) cross sections for Be4+, C6+, N7+ and O8+ projectiles colliding with atomic hydrogen are evaluated employing two different methods: the Classical Trajectory Monte Carlo (CTMC) and the eikonal impulse (EI) approximations. These cross sections are used to extend previously derived scaling laws for n−, nl−, and nlm− distributions to highly excited final levels with 4 ≤ n ≤ 9, covering energies in the range 50-2000 keV/amu. Present results are in agreement with available experimental and theoretical data for these collision systems, becoming a useful instrument for plasma research.

Inelastic processes in low-energy Na+ - Ar, K+ - Ar and K+ - He collisions

SynopsisThe combined experimental approaches, that include a refined version of a condenser plate method, angle- and-energy-dependent collection of product ions, energy loss, and optical spectroscopy, are applied to measure the absolute value of the charge-exchange, ionization, stripping, and excitation cross sections for the collisions of Na+, K+ ions in the energy range of 0.7 - 10 keV with the He and Ar atoms. The correlation diagrams of the (NaAr)+ and (KHe)+ systems have been employed to discuss the mechanisms for these processes.

Measurements and Theoretical Predictions of Charge Exchange Cross Sections and Emission Spectra for O6+ with H2O, CO, CO2, CH4, N2, NO, N2O and Ar

SynopsisRelevant to modeling and understanding X-ray emission from cometary and planetary atmospheres, total charge-exchange cross sections for 1.17 and 2.33 keV/u O6+ ions colliding with H2O, CO, CO2, CH4, N2, NO, N2O, and Ar have been measured and calculated for the processes of single, double, and triple exchanges. Synthetic emission spectra spanning the X-ray, UV, and visible ranges have also been calculated, based on theoretical treatment of the transfer of between one and six electrons from the target neutral to the projectile ion, followed by radiative and nonradiative decay of the resulting highly-excited projectile states.

CTMC Investigation of Capture and Ionization Processes in P + H(1s) Collisions in Strong Transverse Magnetic Fields* *Supported by National Natural Science Foundation of China under Grant Nos. 11104017, 11025417, 11075023, 10974021, 10979007, the Natoinal Basic Research Programm of China under Grant No. 2013CB922200, and the Science and Technology Foundation of Chinese Academy of Engeering Physics under Grant No. 2014B09036

The collision processes of proton with H(1s) atoms, which is embedded in strong transverse magnetic fields perpendicular to the initial velocity of the projectile, are studied with the classical trajectory Monte Carlo method in the energy range 25 keV/u–2000 keV/u and B ∼ 104 T. It is found that the charge exchange cross section is decreased while the ionization cross section is increased significantly. The physics of magnetic field effects is analyzed by the time evolution of electron energy and trajectories, and it is found that these effects are induced by the diamagnetic term in the interaction, continuum electron trapping in the target regions and the Lorentz force. The velocity distributions of the ionized electrons, significantly influenced by the applied fields, are also presented.

Charge state distributions and charge exchange cross sections of carbon in helium at 30–258 keV

With the introduction of helium stripping in radiocarbon (14C) accelerator mass spectrometry (AMS), higher +1 charge state yields in the 200keV region and fewer beam losses are observed compared to nitrogen or argon stripping. To investigate the feasibility of even lower beam energies for 14C analyses the stripping characteristics of carbon in helium need to be further studied. Using two different AMS systems at ETH Zurich (myCADAS and MICADAS), ion beam transmissions of carbon ions for the charge states −1, +1, +2 and +3 were measured in the range of 258keV down to 30keV. The correction for beam losses and the extraction of charge state yields and charge exchange cross sections will be presented. An increase in population of the +1 charge state towards the lowest measured energies up to 75% was found as well as agreement with previous data from literature. The findings suggest that more compact radiocarbon AMS systems are possible and could provide even higher efficiency than current systems operating in the 200keV range.

Empirical regularities in the charge-exchange cross sections of ions with nuclear charges from 5 to 10

A method for empirically estimating cross sections for single-electron loss and capture by ions that are heavy ions in gases is proposed. This method is based on similarity laws for the energy dependences of charge-exchange cross sections. The charge-exchange cross sections of ions with nuclear charges ranging from 5 to 10 in gases with energies ranging from 1 keV/nucleon to 100 MeV/nucleon are obtained. These cross sections can be used to estimate the charge-exchange cross sections in solids if a correction for the substance density is taken into account.

A guided-ion beam study of the collisions and reactions of I(+) and I2 (+) with I2.

Growing interest in developing and testing iodine Hall effect thrusters requires measurements of the cross sections of reactions that generate low energy plasma following discharge. Limited experimental and theoretical work necessitates a decisive experiment to elucidate the charge exchange and collision-induced dissociation channels. To this end, we have used guided-ion beam techniques to measure cross sections for both I(+) + I2 and I2 (+)+I2 collisions. We present total collision cross sections as well as collision-induced dissociation cross sections for center-of-mass collision energies ranging from 0.5 to 200 eV for molecular iodine cations. Similarly, we present total collision cross section and charge-exchange cross sections for atomic iodine cations for center-of-mass collision energies ranging from 0.67 to 167 eV. Time-of-flight measurements of the collision products allow determination of velocity distributions, which show evidence of complex formation of I3 (+) from the I(+) + I2 reaction at collision energies below 6 eV.

Invariant exchange perturbation theory for multicenter systems: Time-dependent perturbations

A formalism of exchange perturbation theory (EPT) is developed for the case of interactions that explicitly depend on time. Corrections to the wave function obtained in any order of perturbation theory and represented in an invariant form include exchange contributions due to intercenter electron permutations in complex multicenter systems. For collisions of atomic systems with an arbitrary type of interaction, general expressions are obtained for the transfer (T) and scattering (S) matrices in which intercenter electron permutations between overlapping nonorthogonal states belonging to different centers (atoms) are consistently taken into account. The problem of collision of alpha particles with lithium atoms accompanied by the redistribution of electrons between centers is considered. The differential and total charge-exchange cross sections of lithium are calculated.

Recoil-ion momentum spectroscopy for He2+ + He electron capture reactions

Electron capture reactions for 3He2+ collisions on He at impact energies in the range 40 keV-300 keV have been studied using the Cold Target Recoil-Ion Momentum Spectroscopy setup which has recently became operational at the Centro Atomico Bariloche. State-selective charge exchange cross sections were obtained and in this work we present recoil-ion transverse momentum distributions. For targets with residual thermal motion, we show that the implementation of a back-projection algorithm based on the transverse momentum distribution component along a direction perpendicular to the jet direction provides results in agreement with those obtained by using previously cooled targets. Present results nicely fit the gaps in the datasets already published by other laboratories and are found to be in good agreement with classical trajectory Monte Carlo simulations.

Theoretical state-selective and total cross sections for electron capture from helium atoms by fully stripped ions

The four-body boundary-corrected first Born (CB1-4B) approximation is used to compute cross sections for single electron capture from helium targets by fully stripped ions. The projectile ions are H+, He2+, Li3+, Be4+, B5+, C6+, N7+, O8+, and F9+. An extensive list of theoretical state-to-state cross sections in these collisions at energies ranging from 20 to 10 000 keV/amu is given. This list includes the state-selective cross sections Qnlm for each individual triple of the usual quantum numbers {n,l,m} of the final hydrogen-like states alongside Qnl and Qn for the pertinent sub-shells and shells where the respective summations over m and {l,m} have been carried out. The maximal value of the principal quantum number n was chosen to vary from 4 (H+) to 10 (F9+) so as to satisfy the condition n≥ZP, where ZP is the nuclear charge of the projectile. Usually, the largest cross sections stem from those values of n that match the projectile charge (n=ZP). The total cross sections for capture summed over all the quantum numbers {n,l,m} are also tabulated. The overall goal of this study is to fill in lacunae in the existing databases of charge exchange cross sections that are needed in several inter-disciplinary fields. For example, in particle transport physics, which is of utmost importance in such emerging branches as hadron therapy, these cross sections constitute a part of the multifaceted input data for stochastic simulations of energy losses of multiply charged ions in matter, including tissue. Other significant uses of the present data are anticipated in charge exchange diagnostics within thermonuclear research project as well as in applications covering the relevant parts of plasma physics and astrophysics.