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Radioactivity and Half-Life

Radioactivity and Half-Life. Radioactivity. An unstable atomic nucleus emits a form of radiation (alpha, beta, or gamma) to become stable. In other words, the nucleus decays into a different atom. Radioactivity. Alpha Particle – Helium nucleus Beta Particle – electron

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Radioactivity and Half-Life

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  1. Radioactivity and Half-Life

  2. Radioactivity • An unstable atomic nucleus emits a form of radiation (alpha, beta, or gamma) to become stable. • In other words, the nucleus decays into a different atom.

  3. Radioactivity • Alpha Particle – Helium nucleus • Beta Particle – electron • Gamma Ray – high-energy photon

  4. Half-Life • Amount of time it takes for one half of a sample of radioactive atoms to decay http://www.absorblearning.com/media/item.action?quick=185

  5. Vocabulary • Daughter isotope • Decay curve • Half-life • Parent isotope • Radiocarbon dating

  6. Half-life • It can be difficult to determine the ages of objects by sight alone. • Radioactivity provides a method to determine age by measuring relative amounts of remaining radioactive material to stable products formed. See pages 302 - 304

  7. Half-life • Carbon dating measures the ratio of carbon-12 and carbon-14. • Stable carbon-12 and radioactive carbon-14 exist naturally in a constant ratio. • When an organism dies, carbon-14 stops being created and slowly decays. • Carbon dating only works for organisms less than 50 000 years old. Using carbon dating, these cave paintings of horses, from France, were drawn 30 000 years ago. See pages 302 - 304

  8. The Rate of Radioactive Decay • Half-life measures the rate of radioactive decay. • Half-life = time required for half of the radioactive sample to decay. • The half-life for a radioactive element is a constant rate of decay. • Strontium-90 has a half-life of 29 years. If you have 10 g of strontium-90 today, there will be 5.0 g remaining in 29 years. See pages 305 - 306

  9. The Rate of Radioactive Decay • Decay curves show the rate of decay for radioactive elements. • The curve shows the relationship between half-life and percentage of original substance remaining. The decay curve for strontium-90 See pages 305 - 306

  10. Medical Applications of Half-Life

  11. Half-Life Calculation #1 • You have 400 mg of a radioisotope with a half-life of 5 minutes. How much will be left after 30 minutes?

  12. Half-Life Calculation #2 • Suppose you have a 100 mg sample of Au-191, which has a half-life of 3.4 hours. How much will remain after 10.2 hours?

  13. Half-Life Calculation # 3 • Cobalt-60 is a radioactive isotope used in cancer treatment. Co-60 has a half-life of 5 years. If a hospital starts with a 1000 mg supply, how many mg will need to be purchased after 10 years to replenish the original supply?

  14. Half-Life Calculation # 4 • A radioisotope has a half-life of 1 hour. If you began with a 100 g sample of the element at noon, how much remains at 3 PM? At 6 PM? At 10 PM?

  15. Half-Life Calculation # 5 • How many half-lives have passed if 255 g of Co-60 remain from a sample of 8160 g?

  16. Half-Life Calculation # 6 • Suppose you have a sample containing 400 nuclei of a radioisotope. If only 25 nuclei remain after one hour, what is the half-life of the isotope?

  17. Half-Life Calculation # 7 • If a radioactive element has diminished by 7/8 of its original amount in 30 seconds, what is its half-life?

  18. Answers to Half-Life Calculations • Half-Life Calculation #1 • 6.25 mg • Half-Life Calculation #2 • 12.5 mg • Half-Life Calculation #3 • 750 mg

  19. Answers to Half-Life Calculations • Half-Life Calculation #4 • 12.5 g, 1.5625 g, 0.09765625 g • Half-Life Calculation #5 • 5 half-lives

  20. Answers to Half-Life Calculations • Half-Life Calculation #6 • 15 minutes • Half-Life Calculation #7 • 10 seconds

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