The contribution fractions of electrons emitted by close collision to the total backward emission yield are 0.5, 0.55 and 0.42 for C, Cu and Al, respectively.

• 由于He+离子的电荷态是变化的，所以还研究了近程碰撞对总的背向电子发射产额的贡献比例，对C、Cu和Al其值分别是0.；5、0