4.Main Content

apparatus

Alpha particle tracks including a collision with a helium nucleus

Alpha particle tracks in wet helium. One collided with a helium nucleus. After the collision, the two tracks are at 90° to each other. That angle only occurs when the colliding bodies have equal masses. The photograph is a lucky choice as the fork occurred directly facing the camera.
 

 
N. Feather (1993) Proc. Roy. Soc., A, vol 141, Pl. 2.