V.A. Khodyrev

Proton energy loss in solids

Abstract The backscattering method is used to measure the 0.1–6.0 MeV proton stopping cross sections. The results obtained are compared with the data published elsewhere and with the Andersen-Ziegler semiempirical curves.

Monte Carlo simulation of ion-beam channeling in YBa2Cu3O7

Abstract A Monte Carlo program (UPIC) for the simulation of ion channeling in crystals with complex structure is described. The program is applied to simulate the channeling of 1.5 MeV He+ and 1 MeV D+ near the [001] axis of YBa2Cu3O7 assuming strongly correlated atomic displacements along the [001] Cu-O rows in the superconducting state. The values for the abrupt change in the half-width of the channeling dip observed in experiments [R.P. Sharma et al., Phys. Rev. B 38 (1988) 9287] at the temperature of the superconducting transition, Tc, are reproduced in the simulations with correlation coefficients of 0.8–0.9. The increase in the minimum channeling yield at Tc found in measurements [T. Haga et al., Phys. Rev. B 41 (1990) 826] can be qualitatively explained by the increase in dechanneling rate due to correlations.

Impact-parameter dependence of energy loss in light ions scattering by a gold atom

Abstract In the measurement of energy loss Q within the collision parameter interval 0.02 A ≲ b ≲ 0.4 A a plateau of the curve of Q ( b ) at b ≲ 0.1 A has been revealed which may be associated with the polarization of the electronic shell of a gold atom.

The Coulomb explosion of molecular ions in channeling conditions

The backscattering energy spectra of protons have been measured with 650 keV/atom H þ ,H þ and H þ beams irradiating Si crystal in h 100 i and h 110 i directions. The Coulomb explosion of molecules on entering a crystal results in significant modification of the transverse energy distribution of channeled protons, the molecular fragments. This shows itself as a significant increase of the dechanneling rate as compared with the case of atomic ion beam. Relative to H þ , the observed backscattering yield for H þ and H þ is substantially higher, up to 30% in the latter case. The data show that the Coulomb explosion appears to be more effective for H þ molecular ions. The measurement results are compared with the corresponding computer simulation. The calculations demonstrate, particularly, the character of coordinated motion of the molecular fragments predetermined by the correlated initial conditions at the crystal surface. 2002 Elsevier Science B.V. All rights reserved.

Stopping cross sections of 80- to 500-KeV protons in phosphorus compounds

Abstract The cross sections for the stopping of 80-500 keV protons in InP, GaP, and ZnSiP2 have been determined from the backscattering spectra. Using the additivity rule for stopping powers, we have found, from the cross sections obtained, the proton stopping cross sections in phosphorus. Possible corrections to the additivity rule are discussed. A method for their estimation is proposed.

Dependence of energy loss of light ions in Au on scattering angle and target thickness in the energy interval 25 to 500 keV/amu

Abstract The integral energy losses of H+, He+ and He2+ ions in thin gold foils at incident energies 40 to 500 keV have been determined experimentally. Pre-equilibrium stopping in the near-surface metal layers is found. Measurements of the energy loss straggling of protons in Au in the 9–45 nm thickness range are also been made. The straggling data are compard with the theories. The experimental angular dependence of the energy loss for protons are compared with the results of a Monte Carlo simulation of particle penetration through a foil.

Charge-state distribution in close collisions of 3 MeV C2+ ions with Ag and Au atoms

Abstract The charge-state distributions of 3 MeV carbon ions scattered over angles of 40° and 60° from sub-monolayers of Ag and Au atoms evaporated on a substrate and from thick layers of Ag and Au have been measured. A close similarity of the charge distributions in all cases is interpreted as a consequence of achieving an equilibrium-like charge-state distribution in a single ion-atom collision.

Impact-parameter dependence of Barkas correction in energy loss of charged particles

Abstract A method of calculation of Barkas correction to the charged particle energy loss for a given impact parameter, Δ E(b), is developed on the basis of local plasma approximation. It is shown that the anisotropy of wake potential should be accounted for adequate description of the difference between the proton and antiproton stopping cross sections. The results of calculation of Δ E(b) for Si and Au atoms are presented.

REGULAR AND STOCHASTIC MOTION IN THE LATTICE POTENTIAL - CONSEQUENCES FOR AXIAL CHANNELING

Abstract The structure of the Poincare surface of section illustrates the existence of the invariant KAM-tori in the case of motion in a two-dimensional lattice potential, roughly corresponding to the particle-atomic-string interaction in axial channeling. The consequences for the statistical description of the channeled particle flux are discussed.

Study of the higher-order corrections to the impact-parameter dependence of energy loss

A method is proposed to describe the impact-parameter dependence of energy loss in ion‐atom collisions, DEObU, which is based on the local plasma frequency (LPF) approach. In this method, a linear response approach is combined with an explicit description of the energy loss to a free electron. This results in a general scheme of calculation where both the Barkas and Bloch corrections are presented. The calculated stopping cross-sections are in satisfactory agreement with the relevant experimental results. However, a serious disagreement was found by comparing the calculations with our recent results for energy losses in a thin gold foil, measured as a function of exit angle. This data reflect the impact-parameter dependence of energy loss in single ion‐atom collisions. To explain this disagreement we address the problem of proper conversion of the impact parameter scale to the angle of deflection in single ion‐atom collisions. It is argued that, due to specific quantum eAects, the deflection angle for a given impact parameter depends significantly on the eventual energy loss. Under the conditions used in the experiment this can lead to an increase by a factor of two of the variation of the energy loss in a foil as a function of exit angle. ” 2000 Elsevier Science B.V. All rights reserved.