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    Nuclear Physics CAP - Revision

    The nuclear model

    • Bohr's model of the atom; each atom is made up of a nucleus, which has the nuclides protons and neutrons, and electrons
      • Protons and neutrons comprise most of the mass (electrons have a negligible mass)
      • Protons are positively charged; neutrons neutral and electrons negatively

    Nuclear Stability

    • The result of the strong nuclear force between nuclides, holding them and therefore the atom together.
      • This opposes the electromagnetic force - like charges (in this case, protons) repel
      • The strong nuclear force is more effective at short distances (something something quark gluon)

    Unstable things

    • Some nuclides are unstable - there are patterns as to why, but we don't have definitive rules - a lot of them just are
      • These ones spontaneously decay
      • Depending on their properties, these nuclides will undergo alpha, beta ($\pm$), or gamma decay
        • This occurs until they become stable nuclides

    Half-Life

    • The time it takes for one half of a sample of a radioisotope to decay
      • The half-life indicates the rate of decay
      • Remember half powering

    Alpha, Beta and Gamma

    • For the below; ionisation refers to the process whereby an atom gains a positive or negative charge by loss or gain of electron

    Alpha

    • Very ionising
    • Stopped by paper
    • Is a helium nuclide
      • $$^{a}{b}X\rightarrow ^{a-4}{b-2}Y+^{4}_{2}\alpha$$

    Gamma

    • Relatively non-ionising
    • Stopped by lead
    • EMR
      • $$^{A*}{Z}X\rightarrow ^{A}{Z}X+^{0}_{0}\gamma$$

    Beta

    • Ionising
    • Stopped by aluminium
    • Extremely energised electrons
    Plus
    • A proton decays into a neutron, a positron and a neutrino
      • $$^{1}{1}P\rightarrow ^{0}{1}\beta + ^{1}_{0}Z$$
    Minus
    • A neutron decays into a proton, electron and an antineutrino
      • $$^{3}{1}H \rightarrow ^{3}{2}He+^{0}_{-1}e$$

    Absorbed dose and dose equivalent

    • Absorbed dose is the amount of radiation that is absorbed by a mass
      • It is measured in milligrays, where grays are the SI unit and calculated $=\frac{E}{m}$
    • dose equivalent accounts for the type of radiation using the quality factor (on the formula sheet)
      • It is measured in millisieverts, where sieverts are the SI unit and calculated $=\frac{E\times quality \space factor}{m}$

    E=mc^2 in binding energy

    • Binding energy is the amount of energy required to bind together the nucleons in a nucleus
    • It is the same amount of energy required to break apart the nucleus
    • If we measure the mass of the nucleus and of its nuclides, the nucleus has slightly less mass
      • This is because mass - mass defect - is lost when forming the nucleus because some of it is converted to energy - the binding energy