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Understanding Radioactive Decay and Half-Life

Learn about radioactive isotopes and how they decay over time, as well as the concept of half-life and its application in determining the age of rocks and artifacts.

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Understanding Radioactive Decay and Half-Life

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  1. Key vocab: What is a Radioactive Isotope? What is Radioactive Decay? What is Half Life?

  2. Radioactive Isotopes Radioactive elements are unstable. They decay, and change into different elements over time. Not all elements are radioactive. Those that are and are the most useful for geologic dating are: U-238 (Uranium) Half-life = 4.5 Billion Years K-40 (Potassium) Half-life = 1.25 Billion Years C-14 (Carbon) Half-life = 5, 730 Years

  3. Radioactive Decay and Half Life Here are some facts to remember: • The half-life of an element is the time it takes for half of the material you started with to decay. • 2. Each element has its own half-life

  4. Radioactive Decay and Half Life 3. Each element decays into a new element C14 decays into N14 (Nitrogen) while U238 decays into Pb206 (Lead), etc. 4. The half-life of each element is constant. It’s like a clock keeping perfect time. Now let’s see how we can use half-life to determine the age of a rock or other artifact.

  5. The blue grid below represents a quantity of C14. Each time you click, one half-life goes by and turns red. C14 – blueN14 - red As we begin notice that no time has gone by and that 100% of the material is C14

  6. The grid below represents a quantity of C14. Each time you click, one half-life goes by and you see red. C14 – blueN14 - red After 1 half-life (5730 years), 50% of the C14 has decayed into N14. The ratio of C14 to N14 is 1:1. There are equal amounts of the 2 elements.

  7. The blue grid below represents a quantity of C14. Each time you click, one half-life goes by and you see red . C14 – blueN14 - red Now 2 half-lives have gone by for a total of 11,460 years. Half of the C14 that was present at the end of half-life #1 has now decayed to N14. Notice the C:N ratio. It will be useful later.

  8. The blue grid below represents a quantity of C14. Each time you click, one half-life goes by and you see red. C14 – blueN14 - red After 3 half-lives (17,190 years) only 12.5% of the original C14 remains. For each half-life period half of the material present decays. And again, notice the ratio, 1:7

  9. What is the half life represented in this graph?

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