V.S. Nikolaev

On the equilibrium charge distribution in heavy element ion beams

Abstract Unified approximate semi-empirical formulae for the mean charge. ī . and width. d . of the equilibrium charge distribution in fast ion beams after their passing through solids have been obtained for all particles with atomic number Z ⪆ 20.

Passage of nitrogen and oxygen ions through carbon and celluloid films

Abstract The approach to charge-state equilibrium in v = 8 × 108 cm/s nitrogen and oxygen beams in celluloid and carbon solid films and nitrogen gas targets has been studied experimentally and theoretically. A two-film target has been used to show that the charge exchange taking place at the exit surface is of crucial importance for charge states detected outside solid targets. Electron capture cross sections inside solid targets have been calculated to be an order-of-magnitude lower than in gas targets. It is concluded that only very low lying excited states of the ions are populated within a solid, and that most ions are unexcited at least for near-equilibrium target thicknesses.

Attainment of equilibrium charge distributions in fast ion beams passing through solid films

Abstract The thicknesses Ts of carbon targets needed for equilibration of the charge distribution in H, He and N ions beams have been calculated in the energy range E = (0.03–100) MeV/amu. The calculations have shown that for N ions at E = 0.1 MeV/amu the value of Ts is 20 times Tg in a gas target and that the difference decreases with increasing energy.

On the target thickness to attain equilibrium charge distribution in a beam of fast ions

Abstract The equilibrium thicknesses T of H 2 , He, N 2 and Ar gastargets have been calculated for some ions with nuclear charge Z = 1–92 at energies E = 10 −2 −10 3 MeV/amu. The dependence of T on various parameters is studied. The maximum values of charge distribution halfwidth d are shown to be attainable at target thicknesses lower then equilibrium.

The experimental determination of the impact parameter dependence of inelastic energy loss of channeled ions

Abstract Using the channeling technique, the impact parameter dependence of inelastic energy loss of fast He and N ions in Si has been measured.

METASTABLE STATES OF MULTIPLY CHARGED IONS.

Abstract The lifetimes have been measured and the number of excited states for the helium-like and lithium-like particles contained in the beams of ions 9Be, 11B, 13C, 14N, 16O after passing through a thin celluloid film.

An experimental method for finding the mean equilibrium charge of fast ions in solid media

An experimental method for determining the mean equilibrium charge i∞in of fast ions inside solid targets is suggested. The method consists of measuring the mean charge of ions after passage through the target as a function of their initial charge. The measurements are conducted for two targets, one of which is thinner and the other of which is of the order of an equilibrium target thickness. The measured mean equilibrium charge i∞in of C, N, O, Ne ions with the velosity v = (4–12) × 108 cm/s is in excess of the mean equilibrium charge of ions that have passed through the foils i∞s, which suggests the dominance of the electron capture on the target surface over the autoionization of excited states. As the rate of collisions decreases, the difference between i∞in and i∞s increases.

Ionisation of He atoms by H+, He2+ and Li3+ nuclei

The cross sections, sigma i1 and sigma i2, of single and double ionisation of He atoms by H+, He2+, and Li3+ nuclei with energies ranging from 0.01 to 5 MeV amu-1 are calculated in the independent-electron approximation. The calculations are made for three versions of the probabilities of one-electron transitions to the continuum. The double ionisation of He by nuclei with energies E/A approximately 0.1-Z2 meV amu-1 is mainly due to the independent interaction of each atomic electron with the bombarding nucleus. The values of sigma i1 for all nuclei with E/A>or=0.2MeV amu-1 and of sigma i2 for He2+ and Li3+ nuclei with E/A=0.2-0.5 MeV amu-1 calculated in one of the versions are found to agree with the experimental values. The calculated values of sigma i2 for protons with E=0.2-0.7 MeV and 1.5-4 MeV are respectively higher and lower than the experimental values because the authors calculations were made neglecting the electron correlations.

On qualitative features of generalized oscillator strengths and ionization cross sections in ion-atom collisions

Abstract An exact expression is given for the squared modulus of the matrix element corresponding to the 3s electron transition into continuum states with zero energy. The qualitative features of generalized oscillator strengths and electron loss cross sections for hydrogen-like ions in atomic collisions are considered.

The energy straggling of hydrogen and helium ions in aluminum and polystyrene

Abstract The energy straggling of H+ and He+ ions in aluminium and polystyrene films has been measured in energy interval 0.1–1.2 MeV. A new version of the theory, which takes into account fluctuations of ion charge, is suggested for analysis the results obtained.