physics

• Atom


  Positively charged nucleus (which contains neutrons and protons) surrounded by negatively charged electrons
• Subatomic Particles


  • Proton
  • Neutron
  • Electron
• Electron


  Relative Mass: 0 (0.0005), Relative Charge: -1
• Typical radius of an atom: 1 × 10−10 metres
• Radius of the nucleus is 10 000 times smaller than the atom
• Most (nearly all) the mass of the atom is concentrated at the nucleus
• Electron Arrangement


  • Electrons lie at different distances from the nucleus (different energy levels)
  • The electron arrangements may change with the interaction with EM radiation

  
• Isotopes


  Atoms of the same element, but with different masses, which have the same number of protons but different number of neutrons
• Elements


  All atoms of the same element have the same number of protons
• Neutral Atoms


  Have the same number of electrons and protons
• Atomic Notation


  𝑍𝑍𝑋𝑋±𝑛𝑛𝐴𝐴 , where X is the letter of the element, A is the mass number, Z is the proton number, and N is the charge
• Atoms and EM Radiation

  1. When electrons move to a higher orbit (further from the nucleus), the atom has absorbed EM radiation

  2. When the electrons falls to a lower orbit (closer to the nucleus), the atoms has emitted EM radiation

  3. If an electron gains enough energy, it can leave the atom to form a positive ion
• Dalton said everything was made of tiny spheres (atoms) that could not be divided
• JJ Thomson discovered the electron
• Rutherford realised most of the atom was empty space
• Rutherford Model: Positive nucleus at the centre of the atom, and negative electrons existing in a cloud around the nucleus

  
• Bohr produced the final model of the atom
• Positive charge of nucleus could be subdivided into smaller particles, each with the same amount of charge – the proton
• James Chadwick provided evidence to prove neutrons existed
• Radioactive Decay


  Unstable atomic nuclei give out radiation as they change to become more stable. This is a random process.
• Activity


  The rate at which a source of unstable nuclei decays, measured in Becquerel (Bq)
• Count-rate


  The number of decays recorded by a detector per second
• Forms of Radioactive Decay

  • Alpha (α)
  • Beta Minus (β)
  • Gamma (γ)
  • Neutrons
• Alpha Decay


  • Highly ionising, weakly penetrating (~5cm of air)
• Beta Decay


  • Medium ionising, medium penetration (~50cm of air, sheet of paper)
• Gamma Decay


  • Low ionising, highly penetrating (very far in air, few cm of lead)
• Nuclear Equations


  1. Alpha Decay: 𝑍𝑍𝑋𝑋𝐴𝐴 → 𝑍𝑍−2𝑌𝑌𝐴𝐴−4 + 𝐻𝐻𝑃𝑃24

  2. Beta Decay: 𝑍𝑍𝑋𝑋𝐴𝐴 → 𝑍𝑍+1𝑌𝑌𝐴𝐴 + 𝑃𝑃−10

  3. Gamma Decay: Does not cause the mass or charge to change
• Half-Life


  The time taken for half the nuclei in a sample to decay or the time taken for the activity or count rate of a sample to decay by half
• Half-life cannot be predicted when any one nucleus will decay, but it enables the activity of a very large number of nuclei to be predicted during the decay
• Short Half-Life


  • The source presents less of a risk, as it does not remain strongly radioactive
• Long Half-Life


  • The source remains weakly radioactive for a long period of time
• Net Decline


  Calculate the ratio of net decline of radioactive nuclei after X half-lives
• Contamination


  Radioactive atoms are transferred to an object, lasting for a long period of time
• Irradiation


  Exposing an object to nuclear radiation, but does not make it radioactive, lasting only for a short period of time
• Scientific reports on the effects of radiation on humans need to be peer reviewed
• Background Radiation


  Weak radiation that can be detected from natural / external sources
• Radiation Dose


  Measured in Sieverts (Sv)
• Uses of Radioactivity


  • Tracers (e.g. Technetium)
  • Chemotherapy
• Nuclear Fission


  1. Splitting of a large and unstable nucleus (e.g. uranium or plutonium), releasing energy and neutrons

  2. Spontaneous fission is rare, usually requires absorbing a neutron first

  3. Chain reaction occurs as released neutrons cause further fissions
• Nuclear Fusion


  Two small nuclei fuse to form a heavier nucleus, releasing energy