When a proton is fused with lithium and two alpha particles are formed, how do you know which direction they'll go. I thought they would take roughly the same path as the accelerated proton, but in the explanations of Cockroft and Walton's setup, they show the lithium at a 45 degree angle and the scintillation detector off to the side. See figure two in Cockroft's lecture. If a peice of lithium foil was placed perpendicular to the proton stream, would the alpha particle trajectories be different? Please bear with me, I am an environmental chemist, not a physicist. Edit: I can't beleive I posted this in the wrong subforum. I meant to post this in the high energy physics section. Can a mod please move this?