Direct pair production in heavy-ion—atom collisions

Direct pair production in ∼5-MeV/amu heavy-ion-atom collisions with uranium target atoms is calculated with the plane-wave Born approximation and the semiclassical approximation. Briggs's approximation is used to obtain the electron and positron wave functions. Since pair production involves high momentum transfer $q$ from the moving projectile to the vacuum, use is made of a high-$q$ approximation to greatly simplify the numerical computations. Coulomb deflection of the projectile, the effect of finite nuclear size on the electronic wave functions, and the energy loss by the projectile exciting the pair are all taken into account in these calculations.