Direct pair production by electrons

The total cross section for direct pair production by electrons in the field of a heavy nucleus is calculated, using the Born approximation for the nuclear Coulomb field. The calculation improves on previous calculations of direct pair production in four respects: (1) all of the first-order Feynman diagrams for the process are included, (2) the exchange effect is included, (3) the effect of screening is treated more accurately using the Thomas-Fermi screening function, (4) the integration of the differential cross section is done with increased accuracy. These improvements in the calculation result in a theoretical accuracy of 10-15% for low Z elements, and of the order of 25% for high Z elements, for which the neglected Coulomb corrections are more important. The present results are compared with previous theories and with experiments. It is found that there is reasonable agreement with experiment for energies up to about 1 Bev, but that for higher energies the experimental situation is too uncertain to allow a definite conclusion.