Impact ionization from gold, aluminum and PCB-Z

Impact ionization yields of gold, bare aluminum, and PCB-Z conductive paint, used on the Giotto spacecraft front surface, were measured in a dust accelerator. Iron projectiles with masses between 10 to the minus 15th and minus 10th powers g, and speeds 2 to 50 km/sec were shot onto targets made from these materials. The highest speeds were reached for the smallest particles. The charge yields (no. of electrons or ions emitted/no. of projectile atoms) range from 0.09 for PCB-Z over 0.47 for aluminum to 4.7 for gold. These values apply to an impact speed of 68 km/sec and projectile masses of 10 to the minus 15th power g.