Physics 2.9

• What is nuclear fission?


  When a heavy nucleus such as uranium-235 captures a slow moving neutron and splits into lighter nuclei releasing energy and excess neutrons
• What is nuclear fusion?


  When two light nuclei such as hydrogen collide and fuse to produce a heavier nuclei such as helium releasing energy
• How can fission reactions be controlled?

  With boron control rods that when lowered absorb excess neutrons
• What is used to slow down a neutrons in a nuclear fission reaction?

  Moderator
• Why is a moderator used to slow down neutrons?

  So they can cause further fission events in a chain reaction
• What happens by lowering the control rods during nuclear fission?

  They absorb more neutrons so the reaction is slowed down
• Why is nuclear fusion difficult to achieve on earth?

  Requires high temperature
• does nuclear fusion or fission release more energy?

  Fusion
• What does nuclear fission produce?

  Radioactive materials that need a safe and secure storage
• Nuclear fusion does not produce radioactive waste
• Per kilogram nuclear fusion releases more energy
• Nuclear fusion typically occurs in stars