Brilliant! This is an idea from physicists at St. Mary's University in Halifax, Canada, who used mousetraps and plastic balls to simulate a nuclear chain reaction. To begin such a reaction, you only need to bombard nuclear fuel nucleus with a neutron. In this simulation, the plastic golf balls represent the neutrons, and the loaded mousetraps are unsplited uranium nuclei, or nuclear fuel. When a golf ball is dropped onto the arrangement, it sets the process in action by tripping a single mousetrap. The reaction proceeds until its mousetrap "fuel" is spent and the action fizzles out.
In a nuclear reactor, spent fuel can also end the process. But chain reactions can also terminate when neutrons lose the ability to split further nuclei. This can happen if they have lost or gained too much energy to react, or if they have been absorbed by a neutron-absorbing material like boron.