Fission & Fusion (CIE IGCSE Physics: Co-ordinated Sciences (Double Award))

Extended tier only

• The processes of nuclear fission and nuclear fusion are the splitting and joining of atoms

Nuclear fission

• Nuclear fission is defined as:

The splitting of a large, unstable nucleus into two smaller nuclei

• During fission:
  • A neutron collides with an unstable nucleus
    • The neutron and the nucleus are the reactants
  • The nucleus splits into two smaller nuclei (called daughter nuclei) and two or three neutrons
    • The daughter nuclei and the neutrons are the products of the reaction
  • Gamma rays are also emitted

Nuclear fission process

A neutron is fired into the target nucleus, causing it to split

Nuclear fission of uranium-235

Large nuclei can decay by fission to produce smaller nuclei and neutrons with a lot of kinetic energy

Nuclear fusion

• Nuclear fusion is defined as:

When two light nuclei join to form a heavier nucleus

• Stars use nuclear fusion to produce energy
  • In most stars, hydrogen nuclei (light nuclei) are fused together to form a helium nucleus (heavier nucleus) and massive amounts of energy is produced

Nuclear fusion of hydrogen

Two hydrogen nuclei fuse to form a helium nucleus

• Nuclear fusion requires extremely high temperature and pressure 
  • So fusion is very hard to reproduce on Earth