L.L. Balashova

The impact-parameter dependence of antiproton energy loss

Abstract The dependence of the electronic energy loss of antiprotons on the impact parameter has been studied theoretically. The differences in the energy losses of protons and antiprotons are discussed. The following Z13-corrections are taken into account: the Coulomb deflection correction, the binding (antibinding) correction, and the effect of polarization of the electron cloud by the projectile field.

Analysis of the angular dependence of proton energy loss in thin films

Abstract The experimental data on the emergence-angle dependence of 100–400 keV proton energy loss in thin Au foils are reanalysed taking into account the impact parameter dependence of energy loss and the foil thickness inhomogeneity. The results of computer simulations are presented for different theoretical models.

Influence of channeling on scattering of low-energy antiprotons transmitted through thin crystals

Abstract A computer simulation study of the transmission of low-energy antiprotons through a thin single crystal, along one of the axial directions, is reported. The angular distribution of the scattered antiprotons behind the crystal is analysed. As an example the scattering of 300 keV antiprotons moving along the 〈110〉 axis in 500 A and 2000 A thick silicon crystal is considered. The results of the calculation show the formation of the ring-shaped patterns (doughnuts) for the incident angles of the order of the critical angle for channeling. A comparison of the angular distribution of antiprotons with that of protons is made. It is shown that the randomization of the transverse momentum is much quicker for antiprotons than for protons, which leads to a more uniform azimuthal angular distribution. The blocking effect in the transverse plane, known for protons, is not found for antiprotons. The influence of the doughnut distribution on the results of the transmission experiments with small acceptance angle detectors is discussed.

Energy loss of axially channeled antiprotons

Abstract A detailed study of energy spectra (channeled fraction, most probable energy loss, shape of the spectra) of low energy antiprotons moving in a thin crystal, under axial channeling conditions is performed using a Monte Carlo computer simulation. The results of calculations for antiprotons are compared with those for protons. It was observed that the channeled fraction of the antiproton beam is considerably smaller than that for protons due to strong dechanneling. This fraction as a function of incident angle shows a maximum at angles near ψ = 0.5ψL. Whereas for protons, well aligned with a crystal axis, the energy loss is onsiderably reduced as compared to the random beam, for antiprotons the energy loss is nearly the same as for those in a random direction. The spectra for antiprotons are wider than those for protons and have a high-loss tail. In general the directional effects in energy spectra are less pronounced for antiprotons than for protons.

Axial channelling of low-energy antiprotons

Monte Carlo computer simulation of the passage of antiprotons and protons through a silicon crystal under axial channelling conditions is performed. The energy spectra and angular distribution of channelled protons and antiprotons moving along the (110) direction are calculated and compared. The projectile energy range is from 300 keV to several megaelectronvolts. It is shown that the energy loss corresponding to the maximum of the antiproton spectrum is close to the energy loss of particles moving in a random direction. Moreover, the most probable energy loss of the channelled part of the antiproton beam is slightly less than the random energy loss. The Barkas correction to the energy loss has little effect on the energy spectra of channelled particles and can hardly be studied with this type of experiment. The angular distributions of protons and antiprotons differ considerably. The characteristic features of the angular distribution may serve as evidence of channelling of low-energy antiprotons.

Charge asymmetry in the angular dependence of energy loss in thin foils

Abstract A Monte Carlo simulation of the fast ion transmission through a thin foil is made taking into account the impact parameter dependence of the energy loss in individual ion-atom collisions. The charge asymmetry effects in the energy loss are included. Considerable difference in the ejection-angle dependence of energy loss for protons and antiprotons is predicted.