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Half Life

Physics: AQA A Level, topic 10.6.2

Effective Half Life

There are three different types of half life. They are all linked by an equation.

Physical half life (TP)

Physical half life (TP)

  • Physical half-life (TP) is the time taken for half the initial nuclei in a sample to decay.
Biological half life (TB)

Biological half life (TB)

  • Biological half-life (TB) is the time taken for half the initial sample of material to be excreted from the body by biological means.
Effective half life (TE)

Effective half life (TE)

  • Effective half-life (TE) is the time taken for the rate of decay within the body due to the initial sample to decay to half.
  • The three terms are related using the equation:
  • 1TE=1TP+1TB\frac{1}{T_E} = \frac{1}{T_P} +\frac{1}{T_B}

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