Stabilisation of nucleus

• Fundamental forces acting within the nucleus

  • Electromagnetic force
  • Gravitational force
  • Strong nuclear force (SNF)
• Gravitational force


  • Very weak, acts on mass
  • Always attractive
• Strong nuclear force (SNF)


  • Short range
  • Acts on nucleons to bind the nucleus
• How the strong nuclear force changes with distance between nucleons


  1. For nucleon separations less than 0.5fm, the strong nuclear force is repulsive

  2. Between 0.5fm and 3fm, the strong nuclear force is attractive

  3. Beyond 3fm, the strong nuclear force is negligible
• If two protons are separated by less than 0.5fm


  They will repel
• If a proton and a neutron are separated by 2.5fm


  They will attract
• At a separation of 0.5fm, the strong nuclear force and electromagnetic force are equal
• Forces and their effects

  • Electromagnetic force does not affect a neutron
  • Strong nuclear force has a limited range
  • Strong nuclear force holds nucleons in a nucleus
  • Electromagnetic force tends to make a nucleus unstable
• Alpha decay


  Occurs in heavy nuclei (with more than 82 protons), like uranium
• What happens in alpha decay


  1. A heavy nucleus emits an alpha particle (2 protons and 2 neutrons)

  2. The remaining nucleus becomes a different element with 2 fewer protons
• Beta-minus decay


  A neutron in the nucleus is converted into a proton, an electron, and an antineutrino
• Electromagnetic Force


  Like charges repel

  Acts at all distances
• Two protons beyond 3fm...


  will repel

  the snf is negligible

  the electromagnetic force is not and like forces relel