HalfLife Intro

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Half-Life Intro
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• With 100g of sulfur-34, how much will be left
  after 4 half-lives?

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• 100?50g?25g?12.5g?6.25g

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• If there are 80g of barium-146, how much will
  remain after 5 half-lives?

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• 80?40g?20g?10g?5g?2.5g

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• After 2 half-lives, how much neon-19 will remain
  if you started with 30g?

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• 30?15g?7.5g

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• Determining the amount that is left

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• With 4,000g of iodine-131,
• (a) how many half-lives have occurred after 32
  days if each half-life is 8 days?
• (b) How much is left?

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• 32/84 half-lives
• 4,000?2,000g?1,000g?500g?250g

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• The half-life of thorium-234 is 24 days and 120
  days have passed.
• How many half-lives have occurred?
• How much is left if we started with 16,000g?

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• 120/245 half-lives
• 16,000?8,000g?4,000g?2,000g?1,000g?500g

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• With 12g of radon-222,
• (a) how many half-lives have occurred after 22.92
  days days if each half-life is 3.82 days?
• (b) How much is left?

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• 22.92/3.826 half-lives
• 12?6g?3g?1.5g?0.75g?0.375g?0.1875g

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• The half-life of plutonium-239 is 24,100 years.
• (a) how many half-lives have occurred after
  96,400 years?
• (b) What percent is left?

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• 96,400 /24,1004 half-lives
• 100?50?25?12.5?6.25

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• The half-life of carbon-14 is 5,715 years.
• (a) how many half-lives have occurred after
  17,145 years?
• (b) What percent is left?

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• 17,145/5,7153 half-lives
• 100?50?25?12.5

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• Determining the age

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• If we started with 28g of carbon-14 in a sample
  but now only have 1.75g,
• How many half-lives have occurred?
• The half-life of carbon-14 is 5,715 years. How
  old is this sample?

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• (a)
• 28?14g?7g?3.5g?1.75g
• Which is 4 half-lives
• (b)
• 4 x 5715 22,860 years old

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• There were originally 48g of radium-226 in a
  sample, but now there is only 0.75g.
• How many half-lives have occurred?
• How much is left if the half-life is 1599 years
  long?

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• (a)
• 48?24g?12g?6g?3g? 1.5g?0.75g
• Which is 6 half-lives
• (b)
• 6 x 1599 9594 years old

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• If we started with 10g of copper-64
• How many half-lives have occurred if only 1.25g
  remain?
• How much is left if the half-life is 12.8 hours
  long?

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• (a)
• 10?5g?2.5g?1.25g
• Which is 3 half-lives
• (b)
• 3 x 12.8 38.4 hours old