Convoy electron production in heavy-ion-solid collisions

The properties of the sharp v vector/sub e/ approx. = v vector cusps observed in the velocity spectrum of convoy electrons (v vector/sub e/) ejected in heavy ion-solid collisions in the ion velocity range (v vector) 6 to 18 au are compared to the properties of analogous cusps observed in binary electron capture to the continuum (ECC) and electron loss to the continuum (ELC) collisions in gases. Apart from a skew toward v vector/sub e/ > v vector, the v-independent convoy distributions observed are very similar to those for ELC and the cusp widths are the same in both cases. While the shape of convoy peaks is approximately independent of projectile Z, v, and of target material, yields in polycrystalline targets (C, Al, Ag, Au) exhibit a strong dependence on Z and v. Coincidence experiments in which convoy electrons are allocated according to emergent ion charge-state q/sub e/ show a surprising independence of q/sub e/, mirroring the unweighted statistical emergent charge-state fraction. Coincidence experiments of O/sup 6 +/ /sup 7 +/ /sup 8 +/ ions traversing < 110 > and < 100 > channels in Au show a strong yield suppression and a dependence of yield on the channel chosen. Interpretation of these observations, comparisons to convoy production studies using protons, and a discussion of remaining puzzles is given. The history of ECC, ELC, and wake-riding models of convoy electron production is also reviewed

Strong forward-backward asymmetries in electron emission from overlapping resonance states in fast C/sup 3 +/ on He collisions

Autoionizing electrons from the configuration 1s/sup 2/2pnl produced by transfer and excitation were measured for 2.5 to 5.0 MeV C/sup 3 +/ + He-gas collision employing the method of zero-degree Auger spectroscopy. The elctron analyzer was operated with an energy resolution of 300 MeV (FWHM), which corresponds to the projectile rest frame energy resolution (approx.40 MeV). (WRF

Energy dependence of double photoionization in He

The ratio of double-to-single ionization of He has been measured between 280 eV and 1210 eV to investigate its energy dependence in the intermediate region. The new intermediate energy measurement, compared with the most recent theories of Pan and Kelly and of Hino and Hino et al., show the importance of including not only ground state but also final state correlations. They also appear to indicate the importance of including higher-order effects in the theory. The previously reported [11, 22] high energy measurements between 2-12 keV give a ratio of 1.5 (2)% in good agreement with older shake calculations of Byron and Joachain and of Åberg, as well as with recent many-body perturbation theory of Ishihara et al., calculations of Dalgarno and Sadeghpour, and of Andersson and Burgdörfer. In contrast to the intermediate energy behavior, consideration of final state correlations proves inessential as discussed by Dalgarno and Sadeghpour

Newly appreciated roles for electrons in ion-atom collisions

Since the previous Debrecen workshop on High-Energy Ion-Atom Collisions there have been numerous experiments and substantial theoretical developments in the fields of fast ion-atom and ion- solid collisions concerned with explicating the previously largely underappreciated role of electrons as ionizing and exciting agents in such collisions. Examples to be discussed include the double electron ionization problem in He; transfer ionization by protons in He; double excitation in He; backward scattering of electrons in He; the role of electron-electron interaction in determining beta parameters for ELC; projectile K ionization by target electrons; electron spin exchange in transfer excitation; electron impact ionization in crystal channels; resonant coherent excitation in crystal channels; excitation and dielectronic recombination in crystal channels; resonant transfer and excitation; the similarity of recoil ion spectra observed in coincidence with electron capture vs. electron loss; and new research on ion-atom collisions at relativistic energies

CONVOY ELECTRONS IN COINCIDENCE WITH OUTGOING PROJECTILE CHARGE STATES OF Ni (15.6 MeV/u)

Nous avons étudié le nombre des électrons convoyés Ye(qf) en fonction de l'épaisseur (ρx) des cibles de carbon pour des projectiles incidents Niqi+ (15.6 MeV/u) avec qi=27 et 28 en coincidence avec les projectiles émergeant de la charge qf=28 et 27. Simultanément nous avons mesuré la distribution d'etats de charge F(qf, ρx) en fonction de la charge incident qi. Le domaine d'equilibre de charge est obtenu pour une epaisseur de cible plus grande que 650 µg/cm2. Dans le cadre du model des électrons convoyés la ρx dependance de Ye(qi,qf) peut être expliquer si on tiend compte les deux processus ECC et ELC. Il faut introduire une longueur de transport λc, qui est douce fois plus grande que la longueur de la atténuation λe des electrones libres.We have studied the target thickness (ρx) dependence of the convoy electron yield Ye(qf) for the incident projectiles Niqi+ (15.6 MeV/u) with qi=28 and 27 on carbon foils in coincidence with the outgoing projectiles with charge qf=28 and 27. Simultaneously the charge state evolution F(qf, ρx) dependent on the incident charge qi has been measured. For this collision system the charge state distribution saturates for target thicknesses larger than 650 µg/cm2. In the framework of the model for convoy electron production and transport the ρx dependence of the yield Ye(qi,qf) can be explained by assuming ECC and ELC processes. A transport length λc must be introduced, which is twelf times larger than the attenuation length λe obtained with isotachic free electrons