1. 1 Radioactivity and Half-Life

2. 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. 3 Radioactivity Alpha Particle – Helium nucleus Beta Particle – electron Gamma Ray – high-energy photon

4. 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. Daughter isotope Decay curve Half-life Parent isotope Radiocarbon dating

6. 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. 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. See pages 302 - 304 Using carbon dating, these cave paintings of horses, from France, were drawn 30 000 years ago.

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

10. 10 Medical Applications of Half-Life NuclideHalf-LifeArea of Body I–1318.1 daysThyroid Fe–5945.1 daysRed Blood Cells Sr–872.8 hoursBones Tc–996.0 hoursHeart Na–2414.8 hoursCirculatory System

11. 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. 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. 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. 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. 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. 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. 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. 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. 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. 20 Answers to Half-Life Calculations Half-Life Calculation #6 – 15 minutes Half-Life Calculation #7 – 10 seconds