Thursday March 29, 2012

1. ThursdayMarch 29, 2012 (Half-Life)

2. Bell Ringer Thursday, 3/29/12 Which type of radioactive decay is indicated below? Why? alpha decay

3. Bell Ringer Thursday, 3/29/12 Which type of radioactive decay is indicated below? Why? beta decay

5. Announcements • I will not be available this afternoon after school.

6. Half-Life

7. The Half-Life of Uranium Uranium is the fuel that’s used in a nuclear reactor. When a uranium atoms is broken up (fission) to give off energy, the resulting smaller atoms are also radioactive. Many of these smaller atoms that result from uranium fission are radioactive also and have long half-lives. This means that spent fuel from a reactor stays radioactive for a long time, which is why it’s dangerous. Presently, nuclear waste is stored in special facilities around the country in containers meant to last 100 years.

8. Carbon Dating Plants and animals absorb carbon into their tissues, much of which is C-12 or C-13, the most abundant isotopes of carbon. However, some C-14, which is radioactive, is also absorbed. C-14 decays and has a half-life of 5730 years. By measuring the amount of C-14 remaining in a plant or animal fossil, the age of the fossil can be estimated (if it isn’t too old.)

9. Half Life • No two radioactive isotopes decay at the same rate. • Half-life, t1/2, is the time required for half the atoms of a radioactive nuclide to decay. • For example, radium-226 has a half-life of 1599 years. • Half of a given amount of radium-226 decays in 1599 years. • In another 1599 years, half of the remaining radium-226 decays. • This process continues until there is a negligible amount of radium-226.

10. Half Life • Each radioactive nuclide has its own half-life. • More-stable nuclides decay slowly and have longer half-lives. • Less-stable nuclides decay very quickly and have shorter half-lives, sometimes just a fraction of a second.

11. Half Life Sample Problem Phosphorus-32 has a half-life of 14.3 days. How many milligrams of phosphorus-32 remain after 57.2 days if you start with 4.0 mg of the isotope?

12. Half Life Practice Phosphorus-32 has a half-life of 14.3 days. How many milligrams of phosphorus-32 remain after 57.2 days if you start with 4.0 mg of the isotope?

13. Complete Worksheet Radioactivity, Decay, and Half-Life