On Analytical Fits for Electron Impact Ionisation Cross Sections

Godunov, Alexander; Ivanov, P B

doi:10.1238/physica.regular.059a00277

Cited by 26 publications

(20 citation statements)

References 41 publications

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“…A.6. They seem accurate and reliable enough in the entire range of energies needed for our purposes and are consistent with more recent studies (Godunov & Ivanov 1999;Bartlett & Stelbovics 2004;Mattioli et al 2007). The two vertical bars in this figure represent the energy equal to kT e for the temperatures of the core and halo populations at 1 AU from the Sun.…”

Section: A2 Electron Impact Ionization Of Ne He and Osupporting

confidence: 91%

Modulation of neutral interstellar He, Ne, O in the heliosphere. Survival probabilities and abundances at IBEX

Bzowski

Sokół

Kubiak

et al. 2013

A&A

111

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Context. Direct sampling of neutral interstellar (NIS) atoms by the Interstellar Boundary Explorer (IBEX) can potentially provide a complementary method for studying element abundances in the Local Interstellar Cloud (LIC) and processes in the heliosphere interface. Aims. We set the stage for abundance-aimed in-depth analysis of measurements of NIS He, Ne, and O by IBEX and determine systematic differences between abundances derived from various calculation methods and their uncertainties.Methods. Using a model of ionization rates of the NIS species in the heliosphere, based on independent measurements of the solar wind and solar EUV radiation, we developed a time-dependent method of calculating the survival probabilities of NIS atoms from the termination shock (TS) of the solar wind to IBEX. With them, we calculated densities of these species along the Earth's orbit and simulated the fluxes of NIS species as observed by IBEX. We studied pairwise ratios of survival probabilities, densities, and fluxes of NIS species at IBEX to calculate correction factors for inferring the abundances at TS. Results. The analytic method of calculating the survival probabilities gives acceptable results only for He and Ne during low solar activity. For the remaining portions of the solar cycle, and at all times for O, a fully time-dependent model should be used. Electronimpact ionization is surprisingly important for NIS O. Interpreting the IBEX observations using the time-dependent model yields the LIC Ne/O abundance of 0.16 ± 40%. The uncertainty is mostly due to uncertainties in the ionization rates and in the NIS gas flow vector. Conclusions. The Ne/He, O/He, and Ne/O ratios for survival probabilities, local densities, and fluxes scaled to TS systematically differ and thus an analysis based only on survival probabilities or densities is not recommended, except the Ne/O abundance for observations at low solar activity.

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Section: A2 Electron Impact Ionization Of Ne He and Osupporting

confidence: 91%

Modulation of neutral interstellar He, Ne, O in the heliosphere. Survival probabilities and abundances at IBEX

Bzowski

Sokół

Kubiak

et al. 2013

A&A

111

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“…The BELL model uses the polynomial expansion Σ i B i (1 − 1/ U K ) i with the reduced energy U K = T / I K , I K being the binding energy of an electron in the K ‐shell. As pointed out by Godunov and Ivanov 12 that a better fit to experimental KSICS data may be achieved through using a nonlinear term like exp [Σ i (1 − i / U K ) i ] instead of the aforementioned polynomial expansion for the cross section 11. We propose a semiempirical model by incorporating in its structure the radius of the ionized K ‐shell (from the DM model), the dipole interaction term (from the BELL model), and the aforementioned feature of nonlinear exponential term.…”

Section: Introductionmentioning

confidence: 83%

“…In line with the argument of Ref. 12 in favor of using a nonlinear fitting formula, which usually require less parameters, we have chosen to replace the polynomial expansion in B i (1 − 1/ U K ) i of (5) by an exponential function of the corresponding term in Eq. (6).…”

Section: Outline Of the Dmemp Modelmentioning

confidence: 99%

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Empirical model for the electron impact K‐shell ionization cross section of atoms

Patoary

Uddin

Haque

et al. 2008

Int J of Quantum Chemistry

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“…The empirical model of Bell et al 15 (BELL) with species‐dependent parameters has been used to fit data for light atomic targets, charged or neutral 15, 16. In the BELL model, there is no relativistic ingredient and hence inadequate to deal with EIICS at high‐incident energies.…”

Section: Introductionmentioning

confidence: 99%

Electron impact ionization in K‐, L‐, and M‐shells of atomic targets

Patoary

Uddin

Haque

et al. 2011

Int J of Quantum Chemistry

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ABSTRACT:Recently proposed extension of the empirical model (BELL) of Bell et al. (J Phys Chem Ref Data 1983, 12, 891) with incorporation of the quantum mechanical form of orbital radius from the DM model and a nonlinear feature in addition to the ionic and relativistic corrections is examined for electron-impact single ionization in the K-, L-, and M-shells of ionic and neutral atoms. This leads to the generalization of the parameters of the nonlinear form of the modified BELL (NMBELL) model in terms of the quantum numbers nl of the ionizing orbits. The generalization shows that only three species-independent fitting parameters, dependent only on the orbitals, in the NMBELL model satisfactorily reproduce the electron-impact single ionization cross sections of 42 ionic targets belonging to the He, Li, Be, B, C, O, F, Ne, Mg, Al, P, Ca, and Sc isoelectronic sequences over a wide range of energies up to 200 MeV. The NMBELL model is also found to well account for the L-and M-shell ionization of six neutral atoms up to 1 GeV.

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On Analytical Fits for Electron Impact Ionisation Cross Sections

Cited by 26 publications

References 41 publications

Modulation of neutral interstellar He, Ne, O in the heliosphere. Survival probabilities and abundances at IBEX

Modulation of neutral interstellar He, Ne, O in the heliosphere. Survival probabilities and abundances at IBEX

Empirical model for the electron impact K‐shell ionization cross section of atoms

Electron impact ionization in K‐, L‐, and M‐shells of atomic targets

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