• Radioactive materials lose some of their activity each time a decay event occurs.
  • This loss of activity can be estimated by determining the half-life of an isotope.
  • Half-life is defined as that period of time needed for one-half of a given quantity of a substance to undergo a change.
  • Some isotopes have long half-lives – the half of U-234 is 245,000 years.
  • Other isotopes are shorter – I-131 has a half- life of 8.02 days.
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