University of Virginia
Physics Department

Nuclear Reactions

A Physical Science Activity

Fission: Breaking Up is Hard to Do
Fusion: Why Can't We Just Get Together?


Student Activity




Fusion Model

  1. Take 2 protons (chocolate puffs), and bring them together. In the process of fusing, one proton decays into a neutron and gives off energy. Take 1 proton away and change it into a neutron and energy by eating the chocolate puff (energy for you!) and placing a corn puff neutron next to the chocolate puff proton. This is an isotope of hydrogen called deuterium.
  2. Make another atom of deuterium by the fusion process in step 1.
  3. Each deuterium nucleus now fuses with another proton (add a chocolate puff to each nuclei). The result is an isotope of Helium called He-3.
  4. Now fuse the two He-3 nuclei together (you should have 4 protons and 2 neutrons in your model). This is beryllium-6, but it is unstable and disintegrates into two individual protons and a He-4 nucleus which has 2 protons and 2 neutrons and is known as an alpha particle (represented by the Greek letter alpha: a). Energy in the form of gamma rays (represented by the Greek letter gamma: g) is also given off in the process.
  5. See if you can demonstrate the whole fusion process to a classmate.

Fission Model

  1. Begin by making a model of a Uranium-235 nuclei. You will need 92 protons and 143 neutrons. Compare the size of this nucleus to the size of the nuclei used in the fusion process. Only very large atoms are able to undergo fission.
  2. Take an additional neutron and allow it to be absorbed by the U-235 nucleus. Now the nucleus will split apart. The result of this fission is Krypton-92 and Barium-141and 3 neutrons and lots of energy. Split your U-235 into a nucleus with 36 protons and 56 neutrons to form the Kr-92 and a nucleus with 56 protons and 85 neutrons to form the Ba-141. You should have 3 neutrons left. In a nuclear reaction, the remaining 3 neutrons would trigger 3 more fission events, setting off a chain reaction.