Electron angular and energy distributions in relativistic ion-atom collisions
نویسندگان
چکیده
The projectile ionization of high–Z, hydrogen–like ions has been studied within the framework of first–order perturbation theory, based on Dirac’s equation. In these studies, emphasis was placed on the energy distribution of the emitted electrons as observed within the laboratory frame. For many years, first–order perturbation theory has been applied in order to analyze the excitation and ionization of high–Z projectiles in collision with light target materials [1]. At storage rings, these processes are of particular interest since the ionization of the projectiles leads to a loss of the ions from the beam. Apart from the total ionization cross sections, which were often found in good agreement with first–order computations, however, further details about the ionization mechanism can be obtained by studying the angular and/or energy distribution of the emitted electrons. For the energy distributions, for example, a clear deviation from theoretical predictions [1] were observed by Vane et al. [2] in collisions of 160 GeV/u hydrogen–like Pb ions with an atomic Al target. Since up to the present this ‘discrepancy’ between the relativistic theory and experiment has not been resolved, computation of the differential ionization cross sections became desirable and have been carried out by us during the last few years [3]. For fast collisions, of course, the semi–classical approximation (SCA) is appropriate to describe the motion of the projectile along a straight–line trajectory with well–defined impact parameter b. In this approximation, an ionization of the projectile in the field of target atom may happen owing to the Liénard–Wiechert vector potential. From the first– order amplitudes Afi(b; μi, ms) of this potential, the angle and/or energy–differential electron-emission cross sections are obtained [3] d2σfi dΩfdEf = 2π 2ji + 1 ∑
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