CALCULATION OF THE THRESHOLD LAW FOR SCATTERING OF POSITRONS ON NEGATIVE-IONS

Wannier’s classical theory has been successfully applied to studies of fragmentation functions when the interaction potential was homogeneous. Here, the methods of classical mechanics are applied to cases with a nonhomogeneous interaction potential. In this case an analytic solution is not available. However, the numerical solution can be fitted to an analytic expression. A system is discussed that in its final state consists of a highly excited atom, an electron and a positron (A*+e−+e+). The interaction potential consists of the Coulomb term plus monopole to quadrupole and/or polarisation terms. Near threshold, the cross section is fitted to the form sigma =aEkappa. Results are given for H and He. © 1990 IOP Publishing Ltd.