The total cross section for direct pair production by electronsin the field of a heavy nucleus is calculated, using the Bornapproximation for the nuclear Coulomb field. The calculation improveson previous calculations of direct pair production in fourrespects: (1) all of the first-order Feynman diagrams for theprocess are included, (2) the exchange effect is included, (3) theeffect of screening is treated more accurately using the Thomas-Fermiscreening function, (4) the integration of the differentialcross section is done with increased accuracy. These improvementsin 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 theoriesand with experiments. It is found that there is reasonable agreementwith experiment for energies up to about 1 Bev, but that forhigher energies the experimental situation is too uncertain toallow a definite conclusion.
