I.S. Dmitriev

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.

A semiempirical method for determining the cross sections for the loss of electrons by fast multiply charged ions

Abstract This paper describes a semiempirical method for calculang the cross sections σi,i+m for the loss of one and several electrons by fast multielectron ions, which is based on the results of an analysis of experimental data and theoretical calculations. In the proposed method, from the known values of σi,i+m for various ions one can find the cross sections for the loss of an individual electron σnl which are practically independent of the number of electrons qnl in a shell nl. This makes it possible to calculate the cross sections σnl and the cross sections for the increase in charge, Si = Σmσi,i+m, for any other ion. The values of the cross sections σi,i+m are then extracted from those of Si in accordance with the relative probability Pm for the loss of m electrons. It is suggested that in the region of extremely high ion velocities the cascade filling of inner-shell vacancies is the predominant mechanism for the removal from a multielectron ion of several electrons. Using this method the cross sections σi,i+m (m = 1–5) have been calculated for fast ions of iodine and uranium in nitrogen.

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.

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.

Density effects in heavy ion charge-exchange processes in gaseous and solid targets

Abstract Experimental results on the pre-equilibrium and equilibrium charge distributions in celluloid films for incident Be, B, C, N, O ions are analyzed in order to obtain charge-exchange cross-sections. The determined “effective” cross-sections of electron capture and loss in celluloid together with earlier measured analogous cross-sections in nitrogen allow us to calculate charge fractions Fi(t) depending on the target thickness in solid (celluloid) and gaseous (nitrogen) matter. The absolute values and the ratios Acap=σgi,i−1/σsi,i−1 and Aloss=σgi−1,i/σsi−1,i of electron capture and loss cross-sections in {s} solids (celluloid, carbon) and {g} gases (nitrogen) are under consideration.

Oscillations of the charge exchange cross sections and the average equilibrium charge of helium ions

The electron loss and capture cross sections for helium ions at velocities nu =8-20*108 cm s-1 in helium, nitrogen, neon and argon have been measured and the electron capture cross sections for He+ and He2+ ions in various media have been theoretically calculated in the Oppenheimer-Brinkman-Kramers approximation. It has been found that the dependence of the electron capture cross section on the nuclear charge of the target atoms is oscillating. This phenomenon is caused by the analogous oscillations of the values of the equilibrium charge fraction and the average charge of the fast ions.

Cross sections for the loss of the outer 1s, 2s and 2p electrons for fast multicharged ions

The cross sections sigma i,i+m for the loss of m electrons (m=1, 2, 3) for light ions in helium, nitrogen, neon and argon are measured at ion velocities V=2.7, 4 and 8*108 cm s-1. The values of sigma i,i+m are used to obtain the cross sections sigma i(nl) for outer 1s, 2s and 2p electron loss. It has been shown that in the range of V<or approximately=4*108 cm s-1 the cross sections sigma i(2p) for 2p electron loss are 1.2-3 times the cross sections sigma i(1s) and sigma i(2s) for 1s and 2s electrons at the same electron binding energy. The relations between these cross sections are in qualitative agreement with the variations of the electron binding energy when the electrons are promoted to the quasimolecular states.

Investigation of cross sections for the formation and destruction of negative boron ions

The electron loss and electron capture cross sections σi,i+m and σi,i−m for boron ions and atoms traveling at the velocities V=1.19 and 1.83 a.u. in H2, He, N2, Ne, Ar, and Xe are measured. The known experimental data on these cross sections at velocities near the cross-section maximum are analyzed. It is found that the electron loss cross sections can be described by a formula which was previously derived in the free-collision approximation and takes into account features of both the ions and the ambient atoms. As the nuclear charge Zt of the ambient atoms increases, the cross sections vary nonmonotonically, increasing on average as Ztt1/2. A formula based on the model of independent electrons is proposed for electron capture by ions with small values of the charge i. It describes the dependence of the electron capture cross section σi,i−1 on the mean binding energy of an electron in an ion with the charge i−1. The total electron capture cross section σi,i−1 is proportional to the number of vacancies in the unfilled electron shell nearest the nucleus. The cross sections 0σi,i−1 exhibit substantially nonmonotonic variation with Zt, increasing on average as Zt1/3.

Decrease in the observed excited-ion electron capture cross sections due to autoionization

From measurements of the cross sections for electron capture by fast helium-like ions N5+ produced by three different methods, it has been found that by increasing the number of metastable particles in an ion beam from 3% to 40% the electron capture cross section is decreased approximately twice. The use of results of previous investigations clearly shows that this decrease is due to autoionization of lithium-like ions N4+ produced from electron capture. It is suggested that the autoionization mechanism may also account for the previously observed anomalies in the electron capture cross sections for P5+, Br7+ and I7+ ions and the decreased charge-exchange cross sections for He+ and N+ metastable ions.

Passage of molecular and atomic beams of hydrogen ions through foils

Abstract A model to describe the charge fractions of molecular hydrogen beams having passed through foils is proposed. Calculations were carried out for H 2 + ions with E = 0.5–2.5 MeV/amu passing through carbon foils and results are compared with experiment.