Nuclear Fission Demonstration

Have you ever heard of nuclear fission? It’s what happens when atoms (tiny units of matter) are split into smaller pieces. Most atoms are very stable, meaning they “calmly” exist exactly as they are and have a tendency to remain whole. When they are split into smaller pieces, HUGE amounts of energy are released.

This energy can be used to create electricity at nuclear power plants or for weapons, like the atomic bombs the U.S. dropped on Japan during World War II. So, how does fission work exactly? The video above shows a model, meaning fission isn’t really occurring, but it can give you the general idea.

Atoms are made of particles called neutrons, protons, and electrons. Neutrons are the neutral particles, meaning they have no charge, while protons are positively charged and electrons are negatively charged. One common reaction used for nuclear fission is breaking uranium-235 into barium-141, krypton-92, and 2 individual neutrons.

The number after the element name (235) refers to the number of neutrons present in the atom, and when that atom goes through fission, the same number of neutrons must exist. In the case of uranium-235, 141 neutrons go to the new barium molecule, 92 go to the new krypton molecule, and 2 spare neutrons are released.

These spare neutrons are discharged so quickly and energetically that they collide with more molecules of uranium-235 and the process repeats itself.

How do the mousetraps and ping pong balls model fission? Well, the mousetraps are kind of like the uranium-235 molecules holding onto all of the neutrons and the ping pong balls are kind of like those spare neutrons that are released during nuclear fission. Ready to try it for yourself? Here’s how:


Materials Required

At least 24 mousetraps (more if you want a bigger “reaction”)

25-26 ping pong balls (you want to have 1 or 2 extra neutrons to start it off)

Large box

Adult supervision (Adult supervision at all times please)



  1. First, set each mousetrap with a ping pong ball its hammer. When a mousetrap is set, it is very touchy and can snap with the slightest touch. This step can be tricky and it would be best if this was set up by an adult.
  2. As each mousetrap molecule is set, place them inside the large box in a 6×4 arrangement (or similar pattern if using more).
  3. Once all “molecules” are ready, drop the “spare neutron” ping pong ball into the box to begin the fission reaction. If the first one does not set it off, drop the other.