The Nucleus

• The basic structure of an atom comprises a small central nucleus consisting of protons and neutrons (nucleons) surrounded by electrons.
• Isotopes are atoms of the same element that have different mass numbers. (chemically identical, physically different)
• Nucleus is held together by the Strong Force
• Color force holds quarks together creating baryons
• Nuclear force holds baryons together creating atomic nuclei

Radioactive decay

• Unstable nuclei will undergo radioactive decay in which particles and/or electromagnetic radiation are emitted.
• In alpha decay, an unstable nucleus emits an alpha particle
• In beta minus decay, an unstable nucleus emits an electron


• In beta plus decay, an unstable nucleus emits a positron

Radioactive half life

• The number of radioactive nuclei in a sample of a given isotope decreases exponentially with time.
• Half-life is the time required for half of the radioactive nuclei in a sample to decay.
• The half-life of radioactive nuclei is independent of both the physical state and the chemical state of the material.
• The activity of a radioactive substance is the number of radioactive nuclei that decay per unit time.
• The range of products of nuclear decay, some with long half-lives, means that nuclear waste must be stored for long periods.

Induced nuclear reactions

• Nuclear fission can be induced in some heavy nuclei by the capture of a neutron.
• The nucleus splits into two nuclei and several neutrons.
• The total mass of the reactants in a fission reaction is greater than that of the products, releasing energy given by
  E=mc²
• Chain reactions occur due to release of multiple neutrons in nuclear fission
• Nuclear fusion is the process in which two nuclei combine into a single nucleus.

Home page / Stage 1 home page