Calculations of the cross section for single-quantum annihilation of positrons by $K$-shell electrons in the Coulomb field of a nucleus are presented. Numerical results are given for nuclear charges $Z=73, 74, 78, 79, 82, \mathrm{and} 90$ and for energies from threshold to 1.75 MeV. For $Z=82\mathrm{}$ the numerical results agree well but not in detail with previous results of Jaeger and Hulme, and show that the Born approximation is too large by a factor of nearly 2.

• Received 2 March 1964

DOI:https://doi.org/10.1103/PhysRev.135.A1232