Electron-impact excitation and ionization cross sections for ground state and excited helium atoms

Comprehensive and critically assessed cross sections for the electron-impact excitation and ionization of ground state and excited helium atoms are presented. All states (atomic terms) with n4 are treated individually, while the states with n5 are considered degenerate. For the processes involving transitions to and from n5 levels, suitable cross section scaling relations are presented. For a large number of transitions, from both ground and excited states, convergent close coupling calculations were performed to achieve a high accuracy of the data. The evaluated/recommended cross section data are presented by analytic fit functions, which preserve the correct asymptotic behavior of the cross sections. The cross sections are also displayed in graphical form.     

Pure ionization cross section of helium and ionization mechanism

Pure target ionization was investigated for 0.4-6.4 MeV C^q+(q = 1-4) + He and O^q+(q = 1-4) + He collisions. The double-to-single target ionization ratios R₂₁ were measured using coincidence techniques. We compare our results with existing experimental results and find they are in good agreement. The ratio R₂₁ is nearly independent of projectile charge state. The relation of R₂₁ ∼ V is analyzed using the over barrier model (OBM) and ionization probability, which is described in our extended over barrier model. Our calculation agrees well with the experimental results.     

The role of projectile interactions in triply differential cross sections for excitation-ionization of helium

We report triply differential cross section (TDCS) for the simultaneous excitation-ionization of helium by electron impact for both coplanar and non-coplanar geometry. In the coplanar case, calculations have been performed for an incident energy of 500 eV and low ejection energies (3 and 10 eV), whereas in the noncoplanar case we have considered impact energies in the range 1240-4260 eV for a symmetric geometry. The present calculation is based on the eikonal approximation due to Glauber. We have incorporated the effect of post-collision interaction in the Glauber approximation. A comparison is made of the present calculations with the results of other theoretical methods and recent experiments. The Glauber results are in reasonably good agreement with the experiment for small scattering angles.     

Aggregates of atoms and their stopping cross sections

The problem of deriving universal atomic stopping cross sections from measurements performed in real physical targets is discussed with regard to the influence of the bonds on the stopping cross sections, which exists whenever atoms join to form molecules or a solid. This influence has to be considered for all investigated substances, except for the noble gases. The influence of the bonds on the stopping cross sections, which may lead to an observable deviation from Bragg's rule, can be quite large. In addition to the direct influence of the bonds, aggregates of atoms in the form of liquids or solids have a stopping cross section which differs from that of the same substance in the gaseous state, the so-called physical state effect. We show that a separate determination of these influences is not possible from experimental results alone, which means that it is not possible in general to extract stopping cross sections referring to free atoms from values measured in real physical targets.     

K- and L-shell ionization cross sections for protons and helium ions calculated in the ecpssr theory

Ionization cross sections for K and L subshells are tabulated according to target atomic number and incident ion energy. Proton and helium ion energies between 100 keV and 10 MeV and selected targets between C and Am for the K shell and between Ar and Am for the L subshells are used. The cross sections have been calculated in the plane-wave Born approximation (PWBA) with corrections for energy loss (E), Coulomb deflection (C), perturbed stationary state (PSS), and relativistic (R) effects (ECPSSR).     

Excitation, ionization, and electron capture cross sections for collisions of Li with ground state and excited hydrogen atoms

Using the available experimental and theoretical data, as well as the established cross section scaling relationships, a comprehensive cross section database for excitation, ionization and electron capture in collisions of Li³⁺ ions with ground state and excited hydrogen atoms has been generated. The critically assessed cross sections are represented by analytic fit functions that have the correct asymptotic behavior both at low and high collision energies. The derived cross sections are also presented in graphical form.     

Theoretical estimate of the fast-neutron fission cross sections of235,238U

Institute of Physics and Power Engineering. Translated from Atomnaya énergiya, Vol. 76, No. 3, pp. 201–205, March, 1994.     

Triple differential cross section for the ionization of helium by electronic impact

We report results of analytical triple differential cross sections (tdcs) for the single ionization of the helium iso-electronic ions by the electron impact. A two variational parameters wave function is used to evaluate the tdcs. This study shows the accuracy of the tdcs for helium atom and helium like ions in the first Born approximation (fba) at high incident energy domain. The theory is quite acceptable as a fast calculation of the triple differential cross section, particularly at high energies where other theories and methods are cumbersome. A comparison is made of our calculations with previous results of the other theoretical methods and experiment. The fba results obtained here with the two variational parameters wave function are in good agreement with the experiment data at high incident energy. The results show that the electron correlation effects are important around the maxima and influence only the extrema magnitude but not their positions. The calculations presented here are extanded to the cases where the energies of the outgoing electrons are more equal.     

Differential cross sections for ejection of electrons from argon by protons

Measured cross sections for ejection of electrons from argon gas by protons of 5 keV to 5 MeV energy are given as a function of the angle and energy of ejection. These doubly differential cross sections are integrated to obtain cross sections differential in either angle or energy, total electron production cross sections, and mean energies of ejection.