Physics Homework Help

Alpha particles are routinely accelerated using a particle accelerator and are directed with the use of magnets into targets composed of various elements. The Rutherford experiment has a beam of alpha particles incident on a target of gold. An alpha particle (a helium nucleus) is accelerated to a certain speed/makes an elastic head-on collision with a stationary old nucleus?  What percentage of its original kinetic energy is transferred to the gold nucleus?