Total Loss Cross Sections Research Articles

Effects of autoionization in electron loss from heliumlike highly charged ions in fast collisions with atomic particles

We study theoretically single electron loss from helium-like highly charged ions involving excitation and decay of autoionizing states of the ion. Electron loss is caused by either photo absorption or the interaction with a fast atomic particle (a bare nucleus, a neutral atom, an electron). The interactions with the photon field and the fast particles are taken into account in the first order of perturbation theory. Two initial states of the ion are considered: $1s^2$ and $(1s2s)_{J=0}$. We analyze in detail how the shape of the emission pattern depends on the atomic number $Z_{I}$ of the ion discussing, in particular, the inter-relation between electron loss via photo absorption and due to the impact of atomic particles in collisions at modest relativistic and extreme relativistic energies. According to our results, in electron loss from the $1s^2$ state autoionization may substantially influence the shape of the emission spectra only up to $Z_{I} \approx 35-40$. A much more prominent role is played by autoionization in electron loss from $(1s2s)_{J=0}$ where it not only strongly affect the shape of the emission pattern but also may substantially increase the total loss cross section.

Collisions of Be, Fe, Mo and W atoms and ions with hydrogen isotopes: electron capture and electron loss cross sections

This work is a continuation of an investigation of the collisional properties of heavy-ion plasma impurities and the elements used for the plasma facing components in fusion devices. Results on the charge-changing cross sections for W atoms and ions are published in (Tolstikhina et al 2012 J. Phys. B: At. Mol. Opt. Phys. 45 145201). Here we present the electron loss and electron capture cross sections for collisions of Be, Fe and Mo atoms and their ions with the hydrogen isotopes (H, D, T) calculated in the E = 10 eV/u–10 MeV/u energy range. The calculations are performed, accounting for the multiple-electron loss processes and the cross sections, which can contribute more than 50% to the total loss cross sections. The influence of the isotope effect (mass dependence) (Stolterfoht et al 2007 Phys. Rev. Lett. 99103201) on the capture cross sections is also studied in the frame of an adiabatic theory of transitions in slow collisions. New data on the partial multiple-electron loss cross sections for W and W+ are presented. Calculated cross sections are compared with the available experimental and theoretical data.

Projectile-electron loss in collisions with hydrogen at relativistic impact energies

We consider electron loss from hydrogen-like projectiles in elastic and inelastic collisions with atomic hydrogen target. The projectiles move at relativistic velocities v and have atomic numbers Z p which are not very high ( Z p ≪ v). In the elastic collision mode, where the target remains in the ground state, the projectile electron is removed by the interaction with both the target electron and the target nucleus. The inelastic collision mode, in which the target is excited or ionized, is governed by the electron–electron interaction and gives more than 50% of the target contribution to the total loss cross section. Within this mode the loss cross section is dominated by collisions in which the target gets ionized. At sufficiently high impact energies both the elastic and inelastic contributions to the loss cross section become independent of the energy.

Cross sections for charge change in argon and equilibrium charge states of 3.5 MeV/amu uranium ions passing through argon and carbon targets

Cross sections for single and multiple electron capture and loss were measured for 3.5MeV/amu uranium ions, traveling in argon gas, as a function of incident charge state. Multiple electron loss in single collisions was found to contribute significantly to the total loss cross section. The measured cross sections were used to determine the average equilibrium charge in argon by three different methods. The resulting charges were in good agreement with each other and with the effective charge calculated from stopping powers. In order to investigate the gas–solid (density) effect on the average equilibrium charge, the charge distributions of 3.5MeV/amu uranium ions emerging from carbon foils of different thicknesses were measured. It was found that the average equilibrium charge of the uranium ions emerging from the solid is 41% larger than that of the uranium ions emerging from the gas. The energy dependences of the average equilibrium charges for uranium ions exiting carbon and argon targets were examined by combining the present results with previous results of other investigators and compared with the predictions of a semiempirical formula developed recently by Schiwietz and Grande.

Electron loss from 0.74- and 1.4-MeV/u low-charge-state argon and xenon ions colliding with neon, nitrogen, and argon

Absolute total-, single-, and multiple-electron-loss cross sections are measured for $({\mathrm{Ar}}^{+}\ensuremath{-},$ ${\mathrm{Ar}}^{2+}\ensuremath{-},$ ${\mathrm{Xe}}^{3+})\ensuremath{-}(\mathrm{Ne},$ ${\mathrm{N}}_{2},$ Ar) collisions at 0.74 and 1.4 MeV/u. In addition, a many-body classical trajectory Monte Carlo model was used to calculate total- and multiple-electron-loss cross sections for ${\mathrm{Ar}}^{+}$ impact. For ${\mathrm{N}}_{2}$ and Ar targets, excellent agreement between the measured and calculated cross sections is found; for the Ne target the experimental data are approximately 40% smaller than the theoretical predictions. The experimental data are also used to examine cross-section scaling characteristics for electron loss from fast, low-charge-state, heavy ions. It is shown that multiple electron loss increased the mean charge states of the outgoing argon and xenon ions by 2 and 3 respectively. The cross sections decreased with increasing number of electrons lost and scaled roughly as the inverse of the sum of the ionization potentials required to sequentially remove the most weakly bound, next most weakly bound, etc., electrons. This scaling was found to be independent of projectile, incoming charge state, and target. In addition, the experimental total loss cross sections are found to be nearly constant as a function of initial projectile charge state. As a function of impact energy, the theoretical predictions yield an ${E}^{\ensuremath{-}1/3}$ behavior between 0.5 and 30 MeV/u for the total loss cross sections. Within error bars, the data are consistent with this energy dependence but are also consistent with an ${E}^{\ensuremath{-}1/2}$ energy dependence.

TargetZdependence and additivity of cross sections for electron loss by 6-MeV/amuXe18+projectiles

The dependence of electron loss by 6-MeV/amu ${\mathrm{Xe}}^{18+}$ on target atomic number was investigated by measuring single-collision cross sections for loss of one to eight electrons in targets of the noble gases He, Ne, Ar, Kr, and Xe. The total-electron-loss cross sections were found to increase linearly with target atomic number, but an abrupt slope change was observed to occur between Ne and Kr. Calculated total-loss cross sections obtained using the n-body classical trajectory Monte Carlo method were in good agreement with the measurements. The dependence of the individual cross sections on the number of electrons lost was reasonably well represented by a semiempirical fitting procedure utilizing the independent-electron approximation. Additional measurements performed with a variety of molecular targets provided a rigorous test of cross-section additivity. It was found that the additivity rule works well in this collision regime and that the molecular nature of the target has remarkably little influence on the cross sections.

Electron transfer and ionisation in homonuclear collisions of triply charged Ar and Kr ions

Using the crossed-beams technique we have measured absolute total cross sections for electron transfer and total electron loss (transfer+ionisation) in homonuclear collisions of triply charged Ar and Kr ions. Only a slight dependence on the center-of-mass energy is found for the electron transfer cross section in the energy range of about 15–65 keV. The total loss cross sections at 60 keV center-of-mass energy are significantly lower than the only two values obtained by Kim and Janev [Phys. Rev. Lett. 58 (1987) 1837].

Results which provide detailed insight into microwave scattering properties of melting spongy hail

Detailed measurements at 10 GHz of the total loss cross-sections of simulated particles of spongy hail are presented and compared with modelled results. These new results allow a clear insight to be gained into the relationship between the electromagnetic-wave scattering behaviour and the physical states observed during melting.

Cross Sections for the Destruction of 1 - to 25-keV/NucleonXΣg+1andcIIu3Hydrogen Molecules in Collisions withH2Gas

Measurements of the cross sections for the total loss and the ionization of $X^{1}\ensuremath{\Sigma}_{\mathrm{g}}^{+}$ ${\mathrm{H}}_{2}$ [$1<~E$ (keV/nucleon) \ensuremath{\le} 25] and $c^{3}\ensuremath{\Pi}_{\mathrm{u}}$ ${\mathrm{H}}_{2}$ molecules [$3<~E$ (keV/nucleon) \ensuremath{\le} 20] in collisions with ${\mathrm{H}}_{2}$ gas are reported. The $c^{3}\ensuremath{\Pi}_{\mathrm{u}}$ molecules were formed by electron capture by $\mathrm{H}_{2}^{}{}_{}{}^{+}$ ions in Mg vapor. The total-loss cross section of the $c^{3}\ensuremath{\Pi}_{\mathrm{u}}$ state is about 5 times larger than the total-loss cross section of the $X^{1}\ensuremath{\Sigma}_{\mathrm{g}}^{+}$ state.

Classical treatment of electron loss

The classical impulse approximation is used to calculate the cross section for electron loss from fast projectile atoms. The total loss cross section is the sum of an inelastic contribution which arises from collisions in which the target system is excited or ionized, and an elastic contribution which arises from collisions in which the state of the target system is unchanged. The inelastic contribution may be attributed to electron-electron scattering and its calculation presents no difficulty. The position with regard to the elastic contribution, which is due to electron scattering in the static field of the target, is different. It is inferred from the uncertainty principle that the application of classical mechanics may here lead to serious error, at least for light target systems. Such error is indeed found to occur. However, a classical description of the scattering is remarkably successful in the case of heavy target systems: for example, the derived total loss cross sections in H-Ar collisions do not differ from the corresponding measured cross sections by more than 25% through the impact energy range, 10 kev to 1000 kev, studied. Calculations are also carried out with the target system replaced by a structureless model. Good agreement is obtained with the results of recent measurements which Gilbody et al. (1968) made in the range 60 to 450 kev on loss from metastable helium atoms passing through molecular hydrogen.

Lifetime of a Negative Helium Ion

The lifetime of a negative ion of helium produced from ${\mathrm{He}}^{+}$ by charge exchange in helium gas is measured and found to be 18.2\ifmmode\pm\else\textpm\fi{}2.7 \ensuremath{\mu}sec. This is consistent with the lower limit of 10 \ensuremath{\mu}sec previously determined. Total loss cross-section measurements in the energy range 20-70 keV are reported and compared with a previous published value at 17.5 keV. An investigation is also made of the destruction of the negative ions by thermal photons; this is found to be negligible at the temperatures involved, enabling an upper limit of 2.0\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{2}$ to be set on the photodetachment cross section of ${\mathrm{He}}^{\ensuremath{-}}$.