Brief Description:

A one holed rubber stopper rests on each bail of 45 mouse traps in a symmetrical array surrounded on all sides by clear plastic draft shields and an aluminum cover. A single stopper is tossed into the containment vessel striking one of the mouse traps, tripping it and sending its stopper which strikes another, and so on, setting off a chain reaction.


Illustrates the essential feature of a chain reaction, nuclear or otherwise.

Explanation of Experiment:

In a chain reaction, each step produces the trigger that sets off a subsequent step. One reaction can initiate a long sequence (chain) of similar reactions. If a reaction releases more than one trigger, then the rate at which these reactions occur will increase as long as sufficient reactant remains. In this demonstration, each tripped mouse trap releases a stopper. The released stopper is contained by the draft shields so it can trigger another trap. This generates a chain reaction whose rate at first accelerates and then decelerates as the traps are triggered. This process is a mechanical analog of a nuclear fission chain reaction.

Materials Preparation:

Place a three sided draft shield on a tilted surface movable cart, such as one used to transport a television monitor. Set up an array of 4 x 10 activated mousetraps (e.g. Tomcat or Victor brands) on which a one holed #6 rubber stopper is placed, the center of which is located on the center of the bail of each. Five additional traps may be placed behind this array in a row of three, then a row of two, with stoppers placed similarly. A tall, curved draft shield is then placed in back of this contained array to act as the back wall of the makeshift containment vessel. An aluminum serving tray is placed over the top of the three sided draft shield to act as the ceiling of the containment vessel. The entire setup is covered with opaque plastic table covers to enhance the dramatic effect of the demonstration, and carefully wheeled into the lecture hall so as not to disturb any of the set traps prematurely.


Introduce the concept of nuclear fission and explain that set up on the cart is an example of a nuclear reaction containment vessel – uncover so that the audience gets a chuckle out of the low budget setup being presented. At the back of the setup, throw in a rubber stopper which is aimed to strike one of the mousetraps, and observe.


Though most of the “reaction” is contained, there is some open space out of which a stray stopper may emerge, so goggles are recommended. Setting of mouse traps must be done carefully and not rushed to prevent premature detonation and possible bruised fingers.


All materials used in this demonstration may be reused. Traps should be inspected before use to insure operational integrity.


General Concept:

  • Nuclear Chemistry

Type of Reaction:

  • Nuclear

Primary Reference:

  • Shakhashiri, B.Z. and Schreiner, R., 2008, Shakhashiri Chemical Demonstrations Videos – Instructional Guide