STOPPING POWERS FOR POSITRONS AND ELECTRONS

Stopping cross sections for 20 keV positrons ({ital S}{sup +}) and electrons ({ital S}{sup {minus}}) in a thin (61 {mu}g/cm{sup 2}) Al target have been measured using an electrostatic analyzer. The results yield a ratio {ital S}{sup +}/{ital S}{sup {minus}}=1.15{plus_minus}0.08, in good agreement with the theoretically calculated value of 1.097. A marked dependence of the mean energy loss on an emergence angle has been observed for a thin target, and its origin is interpreted with the aid of Monte Carlo simulations.