Radioactivity

• Activity of a radioactive source

  The number of atoms that decay per second
• Half-life


  The time it takes for the activity/number of undecayed nuclei in a sample of a radioactive isotope to halve
• Random nature of radioactive decay


  • Which nuclei and when it will decay is determined by chance - it is unpredictable
• Radioactive decay plot


  Exponential decay curve
• Decay constant


  The fixed probability of a nucleus decaying in a second
• Unit of decay constant


  s⁻¹
• Equation to calculate activity of 'N' nuclei


  1. A = λN

  2. Where λ is the decay constant
• Activity of a source

  The number of radioactive nuclei it releases per second, or the number of decays per second
• Half life


  The time taken for the number of radioactive nuclei to halve (or for the count rate, or activity, to halve)
• Radioactive decay is a random process - you cannot predict the decay of a particular nucleus, but you can predict how many nuclei will decay from a large source
• Graphing radioactive decay produces an exponential decay curve
• Decay constant (λ)


  The fixed probability of a nucleus decaying in a given time interval
• Iterative calculations for decay in a set time period

  ΔN = -λΔt or ΔN = -λN