Fission & Fusion

What "nuclear energy" means

• An atomic nucleus contains an enormous amount of stored energy, held in place by the strong nuclear force that binds protons and neutrons together
• Any time the arrangement of nucleons in a nucleus changes (by splitting it apart, joining nuclei together, or letting a nucleus decay), some of that stored energy is released
• The three ways to release energy from the nucleus are:
  • Nuclear fission: one large unstable nucleus splits into two smaller nuclei
  • Nuclear fusion: two light nuclei join to form one heavier nucleus
  • Radioactive decay: an unstable nucleus emits an alpha, beta or gamma particle and changes into another nucleus (covered in topics 19 and 20)
• The amounts of energy involved per reaction are millions of times larger than for chemical reactions (combustion, batteries, food). Burning a single hydrogen atom in oxygen releases about 10⁻¹⁸ J; fusing a single hydrogen atom releases roughly 4 million times more

Where nuclear energy is used

• Fission is the basis of every working nuclear power station on Earth, and of nuclear weapons
• Fusion is what powers the Sun and all other stars. Fusion is also being developed as a future energy source on Earth, but no commercial fusion power station exists yet
• Radioactive decay is used in medical tracers, smoke detectors, thickness gauging, and (on a planetary scale) to keep the Earth's interior hot enough to drive plate tectonics