20. Nuclear Physics

20. Nuclear Physics

The Nucleus

  • existence and size demonstrated using the Rutherford -scattering experiment.
  • consists of nucleons (protons and neutrons)
  • isotopes of an element share the same number of protons but different number of neutrons.

Nuclear Reactions

  • nuclear reactions involve two or more reactants.
  • represented using the form:
  • for a reaction that releases energy, mass-energy of reactants = mass-energy of products + E,
    where and m is the mass defect (difference in mass between the products and reactants).
  • binding energy is the energy released when the nucleus is formed from its separate protons and neutrons. The same amount of energy is required to break up a nucleus into its constituent nucleons.
  • binding energy per nucleon () is an indication of the stability of a nucleus, where B.E .is binding energy and A is the nucleon number. You need to know how to sketch its variation with nucleon number. (The following video explains the shape of the  versus A graph and why it peaks at .
  • nuclear fission is the disintegration of a heavy nucleus into two lighter nuclei of comparable mass with the emission of neutrons and release of energy.
    e.g.
  • nuclear fusion occurs when two light nuclei combine to form a single more massive nucleus, leading to the release of energy.
    e.g. 
  • The following quantities are always conserved:
    • proton number & neutron number
    • momentum
    • mass-energy

Radioactive Decay

  • spontaneous and random emission of radiation from a radioactive nucleus.
    • particle - helium nucleus
    • particle - electron
    • particle - electromagnetic radiation

  • where A is the rate of disintegration or activity, N is the number of radioactive nuclei and is the decay constant.

  • where x could represent the activity, number of undecayed particles or received count rate.
  • half-life () is the average time taken for half the original number of radioactive nuclei to decay.
  • From ,


  • You may also use , as shown in the following video.