Ejection of fast electrons following the impact of 45 MeV/u Ni-58(q+) (q=19,28) on solid-foil targets - art. no. 032702

We report absolute cross sections for binary encounter and convoy electron emission. Fast-electron velocity spectra were measured for atomic collision s induced by a 45 MeV/u Ni-58 beam impinging on solid targets by means of t he multidetector ARGOS in a large angular range (from 1.5 degrees to 165 de grees). Different conducting elemental targets (C-12, Al-27, Ni-58 and Ni-6 4, Ag-nat, Au-197) and polystyrene were used. Characteristics of electrons with a velocity close to the beam velocity (convoy electrons) were found to be very sensitive to the incoming charge state of the projectile. Their yi eld increases with the target atomic number. The yield of binary encounter electrons with a velocity of almost twice the beam velocity at small ejecti on angles is roughly proportional to the area density of encountered target electrons. The velocity spectra centroids of these electrons are shifted t owards lower velocities than predicted by simple two-body relatiyistic kine matics. Surprisingly, this effect seems to be mostly independent of target material and thickness. With increasing target atomic number, the high-ener gy tails of the spectra exhibit an unexpectedly large number of very fast e lectrons: A multiple-scattering mechanism involving multiple collision sequ ences of electrons between projectile and target atoms is invoked to explai n this effect. The data also show evidence for an excess of fast electrons in the backward direction.