Fast Charged Projectiles Research Articles

The effect of projectile wave packet width on the fully differential ionization cross-sections

In this paper, fully differential cross-sections for the ionization of helium by fast charged projectiles (100 MeV/u C6+ and 3 MeV protons) are calculated. The projectile is described as a wave packet, and the dependence of the cross-sections on the size of the wave packet (coherence width) is investigated. It is shown that the result depends on the coherence properties of the projectile in agreement with the experimental data for incoherent C6+ and coherent proton projectiles. The most prominent difference between the coherent and incoherent results may be observed for electrons ejected perpendicular to the momentum transfer.

Improved description of the interference effects in the ionization of H2 by fast charged projectiles

SynopsisWe present a new approach for the calculation of differential cross sections for the ionization of diatomic molecules. The transition amplitudes are calculated separately for each atom and they are added coherently. The interference term in this method is separated and can be calculated with more precision than in our previous approach.

Theoretical investigations on the projectile coherence effects in fully differential ionization cross sections

We propose a theoretical investigation method for testing the effect of the projectile beam coherence on single ionization processes in light atoms. The method is carried out in the framework of a first-order approximation, and the results are tested for single ionization of helium produced by fast charged projectiles. Based on the same ionization amplitudes fully differential cross section calculations are performed for coherent and incoherent projectile beams. Projectile coherence effects are investigated through these fully differential cross sections and the interference effects are evidenced through cross section ratios. The obtained results are compared to the available experimental data. By these calculations we confirm that projectile coherence effects may have important role in these ionization processes.

Electron Production by Sensitizing Gold Nanoparticles Irradiated by Fast Ions

The yield of electrons generated by gold nanoparticles due to irradiation by fast charged projectiles is estimated. The results of calculations are compared to those obtained for pure water medium. It is demonstrated that a significant increase in the number of emitted electrons arises from collective electron excitations in the nanoparticle. The dominating enhancement mechanisms are related to the formation of (i) plasmons excited in a whole nanoparticle, and (ii) atomic giant resonances due to excitation of d electrons in individual atoms. Decay of the collective electron excitations in a nanoparticle embedded in a biological medium thus represents an important mechanism of the low-energy electron production. Parameters of the utilized model approach are justified through the calculation of the photoabsorption spectra of several gold nanoparticles, performed by means of time-dependent density-functional theory.

Projectile coherence effects investigated for the ionization of helium

Fully differential cross section calculations for single ionization of helium by fast charged projectiles are performed. Projectile coherence effects are investigated through fully differential electron emission cross section ratios resulting from coherent (quantum mechanical) and incoherent (impact parameter) calculations. The obtained results are compared to the experimental data, as well.

Ionization of water molecules by fast charged projectiles

Single-ionization cross sections of water molecules colliding with fast protons are calculated from lowest-order perturbation theory by taking all electrons and molecular orientations consistently into account. Explicit analytical formulas based on the peaking approximation are obtained for differential ionization cross sections with the partial contribution from the various electron orbitals accounted for. The results, which are in very good agreement with total and partial cross sections at high electron and projectile energies, display a strong variation on molecular orientation and molecular orbitals.

Dynamics of dust-free cavities behind fast projectiles in a dusty plasma under microgravity conditions

The penetration of a dusty plasma by fast charged projectiles is studied under microgravity conditions. The mass and charge of the projectiles are larger than those of the target particles. A projectile generates a dust-free cavity in its wake, whose shape strongly depends on the projectile velocity. The faster the projectile the more elongated becomes the cavity while its cross-section decreases. The opening time of the cavity is found independent of the projectile velocity. For supersonic projectiles, the dynamics of the cavity can be decomposed into an initial impulse and a subsequent elastic response that can be modeled by a damped harmonic oscillator.

Nonadiabatic effects in the irradiation of ethylene

AbstractIn the framework of the time‐dependent local density approximation, applied to valence electrons, coupled nonadiabatically to molecular dynamics of ions, the irradiations of ethylene by laser and fast charged projectiles are studied. We find that the Coulomb fragmentation sensitively depends on the laser frequency and on the charge of the projectile. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Excitation and Ionization of Ethylene by Charged Projectiles

Using the time dependent local density approximation, applied to valence electrons, coupled non-adiabatically to molecular dynamics of ions, the collision process between ethylene and fast charged projectiles is studied in the microscopic way. The impact of ionic motion on the ionization is explored to show the importance of treating electronic and ionic degrees of freedom simultaneously. The number of escaped electrons, ionization probabilities are obtained. Furthermore, it is found that the ionic extensions in different directions show the different patterns.

Semiclassical model for calculating fully differential ionization cross sections of the H2 molecule

Fully differential cross sections are calculated for the ionization of H2 by fast charged projectiles using a semiclassical model developed previously for the ionization of atoms. The method is tested in the case of 4 keV electron and 6 MeV proton projectiles. The obtained results show good agreement with the available experimental data. Interference effects due to the two-centre character of the target are also observed and analysed.

Interaction of fast charged projectiles with two-dimensional electron gas: Interaction and collisional-damping effects

The results of a theoretical investigation on the stopping power of ions moving in a two-dimensional degenerate electron gas are presented. The stopping power for an ion is calculated employing linear-response theory using the dielectric function approach. The collisions, which lead to a damping of plasmons and quasiparticles in the electron gas, is taken into account through a relaxation-time approximation in the linear-response function. The stopping power for an ion is calculated in both the low- and high-velocity limits. In order to highlight the effects of damping, we present a comparison of our analytical and numerical results, in the case of pointlike ions, obtained for a nonzero damping with those for a vanishing damping. It is shown that the equipartition sum rule first formulated by Lindhard and Winther for three-dimensional degenerate electron gas does not necessarily hold in two dimensions. We have generalized this rule introducing an effective dielectric function. In addition, some results for two-dimensional interacting electron gas have been obtained. In this case, the exchange-correlation interactions of electrons are considered via local-field corrected dielectric function.

Charge and Energy Dependences of Ionization and Transfer for Helium in Collisions with Fast Charged Projectiles

The classical method within the independent electron model is employed to investigate (i) charge dependences of single and double ionization for helium by various charged ions Aq+ (q = 1 – 8) at impact energies of 0.64 and 1.44MeV/u, respectively, (ii) energy dependences of transfer ionization for helium by 0.5–3 MeV/u A8,9+ ions impact. The Lenz–Jensen model of the atom is applied instead of the Bohr model of the atom, and the impact-parameter dependences are also introduced into the calculations. Satisfactory agreement is found between theoretical and experimental data.

Ionization–excitation of lithium by fast charged projectiles

Cross sections for the double K-shell vacancy production of lithium atoms in collision with fast charged projectiles are calculated. For these ionization–excitation processes, the relative importance of the different first- and second-order mechanisms and the dependence of the cross sections on the sign of projectile charge are investigated. Our studies confirm the strong influence of electron–electron correlations on the behaviour of the cross sections. The obtained results are in reasonable agreement with the data as observed in recent experiments.

On the relative contribution of the dipole-monopole and dipole-quadrupole corrections to the soft electron emission from atoms in collisions with fast charged projectiles

Soft electron emission in ionization of light atomic targets by fast charged projectiles is considered within the first Born approximation. The dipole-monopole and dipole-quadrupole corrections to the dipole term have been calculated and compared. For ionization of neutral or positively charged atomic targets the dipole-quadrupole term is shown to be the main correction to the dipole term.

Advances and challenges in collisions of fast ions with few-electron atoms

This report reviews the recent theoretical results on the fast ion-few-electron atom collisions obtained in the framework of an approach using the perturbation theory expansion in the scattering potential and the diagonalization approximation for CI-wavefunction of the target atom. The uniform consideration of the electron transitions to states of discrete and continuous spectra is set forth. The results of investigations of the two-electron transitions in helium induced by fast charged projectiles, such as, the total and differential cross sections, mechanisms of electron transitions, interference problem and charge asymmetry of the cross sections, normalization of CI-wavefunctions of the discrete and continuous spectrum states, obtained on the basis of the present approach, are discussed.

Theoretical study of the simultaneous ionization and excitation of helium by fast charged projectiles

Cross sections for the simultaneous ionization and excitation to the 2s state of the helium atom by fast proton and antiproton impact have been calculated. We apply the impact parameter method and use a second-order perturbation approximation. Electron correlation is taken into account in the initial state but is neglected in the final state. The cross sections obtained for protons are higher than those obtained for antiproton projectiles, in accordance with the theoretical findings of Sidorovich (V.A. Sidorovich, J. Phys. B 30 (1997) 2187).

Use of the Operator Approach in the Collisions of Highly-Charged Ions with Few-Electron Atoms

The probabilities and cross sections for the 1s2 1S → 2s2 1S and 1s2 1S → 2s2p 1P transitions induced in collisions of fast charged projectiles with helium atoms have been investigated in the framework of the operator approach to the few-body problem (V A Sidorovich, Physica Scripta, accepted for publication). Calculations have been performed for the case of the 2s2 1S excitation of helium by projectiles with Zp varying from 3 to 9 at collision energy Ep = 1.5 MeV/u. The calculated cross sections are in satisfactory agreement with the available experimental data. The cross section dependence upon the projectile charge is established. The wavefunctions for few-electron atom, satisfying the boundary condition U = 0 (U is the interconfiguration interaction potential) in the past or in the future, and the closure relation for joint system functions are presented.

Shakeoff induced by fast charged projectiles.

We derive a shakeoff-like expression for double ionization induced by fast charged projectiles that includes higher-order contributions of the Born series. The resulting shakeoff amplitude is about twice as large and has the opposite sign when compared to that of the shakeoff term defined by the first Born approximation. This analysis permits the determination of the relative phase between the shakeoff and double-scattering contributions to double ionization.

Interactions of fast HeH+beams with matter

We present experimental results from high-resolution studies of the energy and angle distributions for the breakup products that arise from the dissociation of fast-moving $^{4}\mathrm{He}$${\mathrm{H}}^{+}$ and $^{3}\mathrm{He}$${\mathrm{H}}^{+}$ in thin carbon foils. These results are compared with calculations based on a model for the polarization wakes induced in foils by the passage of fast charged projectiles. We also describe measurements on the transmission of such fast molecular ions through thin foils and present results on the transmission probabilities, energy losses, and angular distributions of the transmitted ions. A mechanism is proposed to account for these observations on molecular-ion transmission. Related studies on the foil-induced dissociation of O${\mathrm{H}}^{+}$, O$\phantom{\rule{0ex}{0ex}}\mathrm{H}_{2}^{}{}_{}{}^{+}$, C${\mathrm{H}}^{+}$, $\phantom{\rule{0ex}{0ex}}\mathrm{H}_{2}^{}{}_{}{}^{+}$, and $^{3}\mathrm{He}_{2}^{+}$ are also briefly reported.