Atomic Structure

• The half-life is the average time taken for the number of radioactive nuclei to halve
• The relative mass of an electron is 1 / 2000
• Electrons can move to higher energy levels if they gain energy. They might gain energy by absorbing light or other em radiation
• Electrons can fall to lower energy levels if they lose energy. This can be given off as em radiation
• The radius of an atom is approximately 1 x 10 ^ -10 m
• Alpha radiation / particle

  structure: 2 protons , 2 neutrons

  relative charge: 2 +

  relative mass: 4

  ionising power: high
• beta radiation / particle

  structure: a fast moving electron

  relative charge: 1 -

  relative mass: negligible

  ionising power: medium
• gamma radiation / particle

  structure: high frequency electromagnetic wave

  relative charge: 0

  relative mass: 0

  ionising power: low
• Penetration of the 3 radioactive decays:

  alpha: stopped by paper

  beta: stopped by a few mm of aluminium

  gamma: stopped by thick lead
• What is meant by the ‘random nature of radioactive decay’?

  Where you can't predict which nucleus will decay next
• nuclear weapons is an example of a man - made source of background radiation
• Explain how the process of nuclear fusion leads to the release of energy:

  • lighter nuclei join to form heavier nuclei
  • Some of the mass of the nuclei is converted to energy
• Explain the advantage of the radioactive waste having a shorter half-life:

  • the waste will decay at a greater rate
  • so the risk of harm decreases quickly
• Explain why contamination of the inside of the human body by a radioactive material that emits alpha radiation is highly dangerous:

  • alpha radiation is highly ionising
  • causing increased risk of cancer/ organ failure / radiation poisoning
  • until the radioactive material is excreted / removed
• Explain the ideal properties of a radioactive source for use in medical diagnosis.

  • short half-life so less damage to cells / tissues / organs / body

  • low ionising power so less damage to cells / tissues / organs / body

  • highly penetrating so it can be detected outside the body

  • emits gamma radiation
• Radioactive decay is a random process by which unstable atoms release ionising radiation to become stable
• A high penetrating radioactive source should be used for medical diagnosis so it can be detected outside the body
• Irradiation is when an object is exposed to radiation but does not become radioactive itself Contamination occurs when radioactive material is deposited on or inside an object or living thing, making it radioactive
• Man made sources of background radiation:

  • Radioactive waste
  • x - rays
  • radiotherapy
  • Nuclear weapons
  • Nuclear disasters
• Advantage of nuclear waste having a short half-life

  • Waste will decay at a faster rate
  • so risk of harm decreases quickly
• activity is the rate at which a source of unstable nuclei decays. It is measured in becquerel ( Bq )
• Count rate is the number of decays recorded by a detector per second. An example of a detector is a Geiger - Muller tube
• Contamination

  • Lasts for a long period of time
  • The source of the radiation is transferred to an object
  • Radioactive contamination is the unwanted presence of radioactive atoms on other materials – the hazard is the decaying of the contaminated atoms releasing radiation
  • E.g. radioactive dust settling on your skin (your skin becomes contaminated)
• Irradiation

  • Lasts only for a short period of time
  • The source emits radiation, which reaches the object
  • Exposing an object to nuclear radiation, but it does not make the object radioactive
  • E.g. radioactive dust emitting beta radiation, which “irradiates” your skin
  • Medical items are irradiated sometimes to kill bacteria on their surface, but not to make the medical tools themselves radioactive