1. Radioactivity AP Physics: M. Blachly

2. Review Balance the nuclear reaction:

3. History Roentgen on Dec 22 1895, "photographed" his wife's hand

4. History: Becquerel In 1896 put his wrapped photographic plates away in a darkened drawer with some crystals containing uranium. the plates were exposed during storage.

5. History: Becquerel This was found to be the case with all compounds containing uranium

6. History: The Curies Marie and Pierre Curie worked in Becquerel’s lab Worked on isolating other elements which show activity All three shared Nobel Prize for their work with radioactivity

7. History: The Curies Had no idea radiation was harmful Marie kept it by her bed because it glowed. Pierre carried a chuck in his pocket to show people he met.

8. History: The Curies Pierre is killed by horse-cart Marie isolated the most radioactively potent element, named radium Wins Nobel prize again by herself.

9. History: Rutherford Used a radioactive source (Pb) to investigate the types of radioactivity

10. Radiation Types Alpha Particles: heavy, positive charge Beta Particles: lighter, negative charge Gamma: no detectable mass, no charge

11. Radiation Types

12. History: Rutherford

13. Discovered that almost entire mass must be centered in a “nucleus” that was unimaginably small

14. History: Other Particles 1930 Paul Dirac predicts the existence of a positron Positron found in 1932.

15. More Particles 1932 Chadwick shot  -particles at Be.

16. Radioactivity Is a random probability event The decay rate is proportional to the number of radioactive nuclei

17. Radioactivity The decay rate can be given by

18. Radioactivity The amount of radioactive nuclei left at any time is given by the function

19. Activity SI unit of activity: Becquerel 1 Bq = 1 decay/sec Traditional Unit: The Curie Activity of 1 gram of Radium 1 Ci = 3.7 x 10 10 Bq

20. Half Life Time it takes for half of the radioactive nuclei to decay

22. Half Life

23. Half-life Determine the activity of a 1 g sample of Ra-226, which has a half-life of 1600 years.

24. Half-life

26. Half-life Example C-14 has a half life of 5730 years. A 50 gram bone sample shows 200 decays/min. Living bone gives an activity of 15 decays/minute/gram. How old is the bone?

27. Half-life Example Solved Bone is about 10,900 years old

28. Activity Levels

29. Your turn A scrap of paper taken from the Dead Sea Scrolls was found (using a mass spec) to have a 14C/12C ratio of 0.795 times that found in plants living today. Estimate the age of the scroll.