Start a chain reaction, or introduce non-radioactive isotopes to prevent one. Control energy production in a nuclear reactor! (Previously part of the Nuclear Physics simulation - now there are separate Alpha Decay and Nuclear Fission simulations.)

Fission: One Nucleus Tab: Fire the gun to shoot a neutron at the Uranium nucleus and make it decay. After the Uranium nucleus decays, press Reset to start over with a new one.

Chain Reaction Tab: Add a containment vessel, fill it with U-235 and U-238, and fire the gun to create a chain reaction. Grab the edge of the containment vessel and drag it in or out to change the size. Notice that U-235 contributes to the chain reaction and U-238 does not. Most of the Uranium in the world is U-238.

Nuclear Reactor Tab: Fire neutrons to create a chain reaction. Moving the control rod adjuster out of the reactor will allow the reaction to spread more quickly.

Click to Run

Source: Nuclear Fission, PhET, University of Colorado at Boulder