R. Laubert

Yield of convoy electrons from solids

Abstract The number of convoy electrons emitted in the forward direction from solid targets of C, Al, Ag. and Au per incident 1–4 MeV/amu H, O, Si, and Ni projectile is reported. As expected, the yield is independent of target thickness and of the incident projectile charge state. We find that the yield is target ( Z ) 2 dependent, increases as Z 1 2.75 ( Z ) 1 is the atomic number of the incident projectile) and decreases as E 1 −2.25 ( E 1 is the incident projectile energy in MeV/amu).

The electron capture cross section of 1.5–3 MeV protons from carbon☆

Abstract Since single collision conditions for electron capture processes cannot be obtained for solid carbon targets, gaseous carbon compounds (CH 4 , C 2 H 2 , C 2 H 4 , C 3 H 6 , C 3 H 6 , and C 4 H 8 ) were used as targets to determine the electron capture cross sections of protons from carbon. Although the statistical uncertainty of the measurement was less than 1%, the pressure determination limited our absolute accuracy to 10–15%. Within this uncertainty, the electron capture cross sections of protons from carbon was independent of the carbon compound used in the experiment. The measured cross sections were 8.6 × 10 −21 , 3.0 × 10 −21 7.4 × 10 −22 cm 2 /atom for proton enrgies 1.5, 2, and 3 MeV respectively.

Convoy electron production in heavy ion-solid collisions

Abstract The properties of the sharp ν c ≌ ν cusps observed in the velocity spectrum of convoy electrons (υe) ejected in heavy ion-solid collisions in the ion velocity range (ν) 6–18 a.u. 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 νe >ν, the ν-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, ν, and of target material, yields in polycrystalline targets (C, Al, Ag, Au) exhibit a strong dependence on Z and ν. Coincidence experiments in which convoy electrons are allocated according to emergent ion charge-state qe show a surprising independence of qe, mirroring the unweighted statistical emergent charge-state fraction Coincidence experiments on O6+ ,7+ ,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.

Charge Transfer of 0.8 MeV/u H+, He+ in Various Hydrocarbon Gases

Systematic variations in total single electron capture cross sections, ¿10(CmHn), for 0.8 MeV/u H+ and He+ on various hydrocarbon gases are interpreted in terms of a model that incorporates intramolecular post-collision-interactions to estimate the reduction in the number of exiting neutral projectiles.

Reduction of the Electron Capture Cross-Section for Protons in Hydrocarbon Cases

The total electron capture cross section of 0.8 - 3.0 MeV protons in various hydrocarbon gases (CHn - C4H , n = 2 - 8) has been measured. We find that the electron capture cross section per carbon atom decreases as the number of carbon atoms per molecule is increased. This reduction amounts to ~7% for 3 MeV protons and is ~ 25% for 0.8 MeV protons. We find no significant change in the electron capture cross section for carbon as the number of hydrogen atoms per molecule is increased. The observed variations in the cross section can be reproduced by assuming that post-collision-interactions destroy the required velocity match between projectile and electron.

Convoy electrons from solids in coincidence with emergent projectile charge state

Following the passage of fast ions through thin solid targets, the velocity distribution of forward ejected continuum electrons, centred at a velocity about that of the projectile, is found to be substantially independent of the emergent projectile charge state. The yield per emergent ion is also found to be independent of emergent ion charge state, arguing critically against a projectile charge-dependent, surface-layer origin for the convoy electrons in question.

Convoy Electrons from Solids in Coincidence with the Final Projectile Charge State

We measure the yield and final velocity distribution of electrons accompanying the projectile exiting from thin solid targets in coincidence with the projectile charge state. We find that the yield per emergent projectile and the longitudinal velocity distribution is independent of the final projectile charge state.