The forced impulse method applied to the double ionisation of helium by collision with high-energy protons, antiprotons and alpha particles

Double ionization of helium is investigated for 60-, 120-, and 420-MeV/u (v/c =0.34-0.72)U +-ion impact. The measured double-to-single ionization ratios indicate that, even for these very high velocities, double ionization of the He target results predominantly from independent interactions of the projectile with both target electrons. It is concluded that the asymptotic high-velocity regime for one-step double ionization (i.e. , "shakeoff") has not yet been reached even for U projectiles at 420 MeV/u, and, in fact, cannot be reached for projectiles with q 7, thereby verifying that the ionic charge is fully as important as the velocity in determining the importance of a given ionization mechanism.PACS number(s): 34.50.Fa

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“…More recently, Reading and Ford [8] have presented ab initio calculations that are consistent with Eqs. (Sa) and (5b).…”

Section: Resultsmentioning

confidence: 65%

Double ionization of helium by high-velocityU90+ions

et al. 1992

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“…For example, the observed differences in the double ionization have been attributed to different ionization probabilities, depending on the sign of the projectile charge, at small impact parameters [14,15]; to the Z 3 term, in accordance with the interference model of McGuire [16]; to the two electrons being removed in uncorrelated events at different internuclear distances [17,18]; and to electron correlation in the initial and final states [1,19,20]. In general, all of these models yielded reasonable agreement at high energies, but overestimated the cross sections at lower energies.…”

Section: Introductionsupporting

confidence: 53%

Empirical formulas for direct double ionization by bare ions:Z=−1to 92

2014

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Experimental cross sections and cross-section ratios reported in the literature for direct double ionization of the outer shells of helium, neon, and argon atoms resulting from bare ions ranging from protons to uranium and for antiprotons are analyzed in terms of a first-and second-order interference model originally proposed by McGuire [J. H. McGuire, Phys. Rev. Lett. 49, 1153(1982]. Empirical formulas for the various contributions to double ionization plus information about the phase difference between the first-and second-order mechanisms are extracted from the data. Projectile and target scalings are also extracted. Total cross sections and their ratios determined using these formulas and scalings are shown to be in very good agreement with experimental data for lower-Z projectiles and impact velocities larger than 1 a.u. For very-high-Z projectiles, the amount of double ionization is overestimated, probably due to saturation of probabilities that is not accounted for in scaling formulas.

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“…(41) is the time-dependent Hartree potential while the third term is the xc potential which, in practice, has to be approximated. As in the static case, the great advantage of the time-dependent KS scheme lies in its computcttional simplicity compared to other methods such as time-dependent configuration interaction [:31]~ [36].…”

Section: (T) = E-w(t)w[n](t)mentioning

confidence: 99%