Radioactive Source - Decay Chains and Multiple Modes

Decay Chains and Multiple Modes

The daughter nuclide of a decay event may also be unstable (radioactive). In this case, it will also decay, producing radiation. The resulting second daughter nuclide may also be radioactive. This can lead to a sequence of several decay events. Eventually, a stable nuclide is produced. This is called a decay chain (see this article for specific details of important natural decay chains).

An example is the natural decay chain of 238U, which is as follows:

  • decays, through alpha-emission, with a half-life of 4.5 billion years to thorium-234
  • which decays, through beta-emission, with a half-life of 24 days to protactinium-234
  • which decays, through beta-emission, with a half-life of 1.2 minutes to uranium-234
  • which decays, through alpha-emission, with a half-life of 240 thousand years to thorium-230
  • which decays, through alpha-emission, with a half-life of 77 thousand years to radium-226
  • which decays, through alpha-emission, with a half-life of 1.6 thousand years to radon-222
  • which decays, through alpha-emission, with a half-life of 3.8 days to polonium-218
  • which decays, through alpha-emission, with a half-life of 3.1 minutes to lead-214
  • which decays, through beta-emission, with a half-life of 27 minutes to bismuth-214
  • which decays, through beta-emission, with a half-life of 20 minutes to polonium-214
  • which decays, through alpha-emission, with a half-life of 160 microseconds to lead-210
  • which decays, through beta-emission, with a half-life of 22 years to bismuth-210
  • which decays, through beta-emission, with a half-life of 5 days to polonium-210
  • which decays, through alpha-emission, with a half-life of 140 days to lead-206, which is a stable nuclide.

Some radionuclides may have several different paths of decay. For example, approximately 36% of bismuth-212 decays, through alpha-emission, to thallium-208 while approximately 64% of bismuth-212 decays, through beta-emission, to polonium-212. Both thallium-208 and polonium-212 are radioactive daughter products of bismuth-212, and both decay directly to stable lead-208.

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