Monte Carlo simulations of slow-positron production from normal and glancing incident targets

A systematic set of Monte Carlo simulations of slow-positron production by energetic electrons impinging on normal and glancing incident targets are presented. The estimated slow-positron production efficiencies are found to increase linearly with incident electron energy when using converters of optimal thickness. The two targets perform equally well below 20 MeV but at higher energies the glancing incident target is more efficient. This increase in efficiency is caused by a decrease in the converter's positron production volume, allowing a larger fraction of low-energy primary positrons to escape from the converter and impinge on the moderators. Further increases in the glancing incident target's efficiency may be possible by altering the arrangement of the converter-moderator system.