1 / 12

7.2 Half-Lives

7.2 Half-Lives. By: HULK And Bruce Banner. Radiocarbon Dating. Used to calculate the age of plant and animal remains While organism alive carbon-14 to carbon-12 ratio stays same When organism dies, carbon-14 decays without being replenished

sorena
Download Presentation

7.2 Half-Lives

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. 7.2 Half-Lives By: HULK And Bruce Banner

  2. Radiocarbon Dating • Used to calculate the age of plant and animal remains • While organism alive carbon-14 to carbon-12 ratio stays same • When organism dies, carbon-14 decays without being replenished • Puny scientists like Bruce Banner measure ratio of carbon-14 to carbon-12 to find how old organism is

  3. Rate of Radioactive Decay • Radioactive decay is measured using half-lives • Half-life is constant for any radioisotope • Half-life is the time it takes for half a sample of a radioisotope to decay • Ex: Strontium-90 has a half-life of 29 years • If you had 100g of strontium, after 29 years there would be 50g left

  4. Decay Curve • Graph of decay of radioisotope • After each half-life, amount of radioisotope drops by half

  5. Decay Curve • For example: • Iodine-131 is used for treating thyroid cancer • It has a half-life of 8 days • Suppose you have 20g of iodine-131 • You can find out how much will remain after 16 days: • 16 days = 2 half-lives

  6. Common Isotope Pairs • Isotope that decays called parent isotope • Stable product(s) of parent isotope's decay called daughter isotope(s) • On next slide, some common isotope pairs that can be used for radioisotope dating

  7. Common Isotope Pairs

  8. Potassium-40 Clock • Potassium-40 has a half-life of 1.3 billion years • It’s daughter isotope is argon-40 • When rock is created from lava, the argon-40 is forced out leaving only potassium-40 • After time the potassium-40 decays and creates argon-40 which gets trapped in the rock • When scientists examine the rock they can use the amount of argon-40 to find the age of the rock • Since these rocks were probably formed at the beginning of the earth’s life, the age of the rock is close to the age of the earth

  9. Potassium-40 Clock • As the amount of potassium-40 decreases, the amount of argon-40 increases • Using the graph and the ratio of potassium-40 to argon-40, scientists can find how old the rock is

  10. Video http://www.youtube.com/watch?v=KWAsz59F8gA

  11. Quiz • Which two isotopes get compared in radiocarbon dating? • What is used to measure radioactive decay rate? • Does a half-life change for a given radioisotope? • What is a decay curve? • What is the daughter isotope of uranium-235? • What happens to the amount of argon-40 as the amount of potassium-40 decreases?

  12. Answers • Carbon-12 and carbon-14 • Half-life • No • A graph of the decay of a radioisotope • Lead-207 • The amount of argon-40 increases

More Related