RELATIONSHIP BETWEEN THE BORN AND IMPULSE APPROXIMATIONS FOR THE ANTISCREENING PROCESS

The relationship between the plane-wave Born approximation (PWBA) and the impulse approximation (IA) for the antiscreening contribution to e lectron loss is studied. It is shown that the IA can be obtained from the PWBA in the case of fast, asymmetric collisions. In this collision regime, it is shown that the broadening of the ''free'' electron beam velocities, taken into account by the Compton profile of the target w ithin the IA framework, can be considered to simulate the sum over the final continuum target states in the PWBA. Thus, these two different theoretical approaches are reconciled. The derivation also brings out some important features of the antiscreening mechanism not easily seen in either approximation.