Secondary electron production versus the incident angle μ = cos(θ) for particles of radii μm, mm and cm. The secondary electron production rises with decreasing μ and experiences a jump at the angle when the positron penetrates all the way through the solid. Finally, the secondary electron production falls when the pathway through the particle is short at very low μ (dotted line). The integrated yield (dashed lines) is about 0.08 for mm and cm solids and 0.04 for μm solids.