Annihilation in positron—atom collisions: A new approach

The method of Hiller, Sucher, and Feinberg for the evaluation of matrix elements of $\delta$-function operators between bound-state wave functions has been extended to scattering states in another paper. The resulting identities can be used to improve the calculation of positron annihilation cross sections whenever an approximate positron-atom scattering wave function is known. In this paper the advantages of the method are illustrated first with the static model for $e^{+}$-H scattering and then with the more realistic polarized-orbital approximation.