Units of Radioactivity

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  • One gram of Radium was the original standard for activity.
  • Use by many people caused a need for standardization for consistency.
  • The first unit of activity was called the “Curie” in honor of Marie.
  • Once measured 1 g of Radium or 1 Ci put out 3.7 x 1010 Disintegrations/second
  • The Ci is based on specific activity not mass.
    • 1 Ci of Lutetium-176 = 880 tons
    • 1 Ci of Ra-226 = 1 g
    • 1 Ci of Co-60 = 1 mg
  • The Ci is not based on Half Life.


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