Higher-order contributions to ionization plus excitation cross sections in high energy e^-+ He and H⁺+ He scattering

Abstract

The authors have determined absolute cross sections for ionization-excitation of He by energetic electron and proton projectiles. Using a semi-empirical analytic formula the authors have been able to decompose their He+ (np) cross section data in leading order terms which are proportional to Zpn for n = 2, 3 and 4. In particular the authors have found a strong Zp3 dependence which appears to represent quantum interference effects. The set of amplitude coefficients obtained here is universal for both their electron and proton cross section results from He+ (np) states with principal quantum numbers n = 2 to 5.

Ionization–excitation of helium to He (2p) magnetic sublevels following electron, proton, and molecular hydrogen (H2 and H3 ) impact

“…There is at present a considerable interest in few-electron processes induced by intermediate to high-energy charged particle impact on atomic and molecular targets (McGuire 1997, Bruch et al 1993 such as double ionization, double excitation (Bruch et al 2002), and ionization-excitation. These many-body aspects of atomic collision processes are associated with electron-electron correlations and other few-body dynamical phenomena that supersede independent-particle models (Niehaus 1986).…”

2.4MeV Cq+on He: Inverse Reaction for Active Diagnostics of Future Fusion Plasmas

“…Since then, the detector has been replaced ; new branching ratio measurements using Li-like ions of C, N, O and F indicated an efficiency curve very similar to the previously established one [28]. The efficiency curve has also been put on an absolute scale by two di †erent experiments : In one measurement (at Bochum) the light yield of radiation of Be under 100 keV proton impact (at K a a wavelength near 13.5 nm) was evaluated [29] ; the other experiment (at Reno) used 1 MeV proton ionization and excitation of He (at j \ 30.378 nm) and compared this to the light yield under electron impact [14,17,18,23,25], following the example of Forand et al [8]. The latter calibration point is very handy for the present measurement and has been used as a (daily) reference for the present study.…”

Electron Correlation Leading to Double-K-Shell Vacancy Production in Li-Like Ions Colliding with Helium

“…Doubly excited states of helium are also hollow states, and were first described by Fano (Fano, 1961). These states have been investigated theoretically and experimentally by many researchers during the past thirty years (Andersen et al, 1986, Bruch et al, 1993, Fulling et al, 1992, Berg et al, 1992. Studies of these states were continuously improved over the years providing new information on the correlated motion o f a pair of electrons in the Coulomb field of the nucleus.…”