Electron capture by ultra-relativistic jets of positrons from atomic targets

Electron capture by ultra-relativistic positrons impacting on hydrogenic ta rgets is theoretically studied. Matrix distorted wave models previously dev eloped for heavy projectile impact are employed. The validity for positron impact is established. The models include matrix distortions to describe th e electron simultaneously in the field of the target nucleus and projectile . Differential and total cross sections for the charge transfer from the K- shell of the target to the K-shell of the projectile at several positron im pact velocities. are shown. The contribution of the Thomas two-step mechani sm to the charge transfer process is discussed. (C) 1999 Published by Elsev ier Science B.V. All rights reserved.