Welcome to practical physicsPracticle physics - practical activities designed for use in the classroom with 11 to 19 year olds
 

Alpha particle tracks including a collision with a helium nucleus

Collision with 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.