1 / 13

Half-lives

Half-lives. Objective 5. Half-lives. The time it takes for one-half of a radioactive isotope (a sample) to decay. Let’s say the half life of isotope A-5 is 1 minute. You have 10 pounds of it. How much is left after 1 half-life? 5 lbs How much is left after the second half-life? 2.5 lbs

nina-barlow
Download Presentation

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. Half-lives Objective 5

  2. Half-lives • The time it takes for one-half of a radioactive isotope (a sample) to decay

  3. Let’s say the half life of isotope A-5 is 1 minute. You have 10 pounds of it. How much is left after 1 half-life? 5 lbs How much is left after the second half-life? 2.5 lbs How much is left after the third half-life? 1.25 lbs How much is left after the fourth half-life? 0.625 lbs How much is left after the fifth half-life? 0.3125 lbs How much is left after the sixth half-life? 0.15625 lbs Does it ever go away??? Example Problem 1

  4. Half-life GraphExponential Decay Tritium = H-3 t1/2 = 4500 days = 12.3 years

  5. Calculating Half Life • AE = Ao * 0.5t/t1/2Where AE = amount of substance leftAo = original amount of substancet = elapsed timet1/2 = half-life of the substance • Note: Unit for time does not matter as long as both as same.

  6. Example • You are given 157 grams of C-14, how much of C-14 would be left after 2000 years? The half-life of C-14 is 5730 years. AE = 157 * 0.5(2000/5730)

  7. Amount of C-14 left after 2000 years would be 123 grams.

  8. Example Problem 2 You have a 100.0 grams sample of Radium-222. It has a half-life of 3.8 days. How many grams will be left after 2 weeks?

  9. 7.8 grams of Radium-222 is left after 2 weeks

  10. References • http://wwwchem.csustan.edu/chem3070/images/tritium.gif

More Related