Discover of Radioactivity

1. Discover of Radioactivity Chemistry 332

2. Where are we? • This story starts in 1895 with the work of the German physicist Wilhelm Roentgen. • He was working with a Cathode Ray tube and noticed something very interesting...

3. Electric current passed through two electrodes and an invisible beam of energy is made Cathode Ray Tube? (With a fluorescent screen the energy path glows green)

4. So What? He was working on his experiment on this side of the room and had a different experiment across the room Chem Rules!

5. And the Cathode ray tube turned on... And a fluorescent screen across the room started to glow! He then flipped the switch... Chem Rules!

6. The screen stopped glowing! So he turned it off... And the Cathode ray tube went dead Chem Rules!

7. And the Cathode ray tube turned on... And again the screen glowed even though the tube wasn’t even aimed at it! So he tried it again! Chem Rules!

8. Conclusion? • The Cathode Ray tube was giving off some sort of energy in all directions!!!! • Roentgen next thought, “I wonder how powerful these energy rays are?” • So he took the fluorescent screen into the next room, came back and flipped the switch….

9. And the switch was flipped and... Sure enough, the screen glowed! The Set-Up Fluorescent screen Cathode ray tube

10. Conclusion Fluorescent screen The tube must be giving off POWERFUL invisible energy Cathode ray tube

11. What are these? • The rays of energy were invisible • They were strong enough to penetrate the wall • They were unprecendented • So he called them…. • X-Rays

12. So Roentgen Discovered X-Rays • X-Ray machines began popping up everywhere • Even shoe stores had them so you could see your feet bones • Some thought they were the Devil’s tool • More importantly they led to further studies

13. Science is moving faster now... • It’s now 1896, one year after Roentgen’s work • Antoine Henri Becquerel has heard of the X-Ray and it’s link to fluroescence and decides to do his own experiments with phosphorescence

14. His Hypothesis • Some phosphorescent materials emit X-rays when exposed to high energy • These x-rays can penetrate substances but are ultimately just like visible light (just stronger)

15. His Set-Up Sunlight Photographic film Would the film be exposed? Yes

16. Thick black paper But…. Sunlight Photographic film Would the film be exposed? No

17. Phosphorescent material It glows! But, but…. Sunlight Photographic film wrapped in thick black paper What happens to the phosphorescent material in the sunlight?

18. This glowing gives off energy • If the energy was just visible light, would the photographic film be exposed? • No, it’s wrapped in black paper the normal light can’t penetrate • If the energy also contained X-Rays, would the photographic film be exposed? • Yes, X-rays are just like light but can easily penetrate the papter.

19. What was the result? • Sure enough, the photographic paper was exposed! • This meant that phosphorescent materials, when glowing due to the energetic effects of the sun, give off X-rays!

20. So what? • Really nothing new happened there with that experiment • But on Feb 26th, Becquerel decided to repeat the experiment but couldn’t due to cloudy skies over Paris.

21. Drats! • Becquerel took the phosphorescent materials and the photofilm wrapped in black paper and stuck them in a drawer. • They stayed there, undisturbed in the dark until March 1st; four full days

22. Let’s Review • Becquerel’s conclusion was that sunlight made the phosphorescent material glow • This gave off penetrating x-rays • This caused the photofilm to be exposed even though it was wrapped in black paper • Should the photofilm, after sitting the dark, wrapped up in black paper be exposed? • No, there’s no light to cause the phosphorescent material to glow and thus give off x-rays

23. Just out of curiosity • Becquerel developed the photographic film anyway. • What did he find? • The photofilm was exposed just as much as his previous experiment! • What does this mean?

24. Sunlight doesn’t matter • The phosphorescent material was spontaneously giving off energy regardless of the sun • This energy was invisible • It was also strong enough to penetrate the black paper • Were these X-rays or some other energy?

25. How many substances do this? • Marie Curie (a student of Becquerel by the way) and Pierre Curie spent years isolating substances that exhibit these properties • But what are they?

26. One last experiment • Ernest Rutherford, using Becquerel’s ideas and material isolated by the Curies performed an experiment on the X-rays found by Roentgen as well as the energy found by Becquerel

27. His Set-Up + Strong magnet - X-ray or other energy source

28. Passed straight through with no deflection The results! + Strong magnet - What charge are X-rays, then? X-rays Neutral, just like light

29. Split into three different beams! The results! + Strong magnet - What charges are these? The energy discovered by Becquerel and the Curies Positive, negative, and neutral

30. What is this? • This mysterious energy given off by the fluorescent substances was of three different types • It was given off spontaneously • It was invisible • It was of very high energy • What is it?

31. I’ll give you a hint • The fluorescent ore used by Becquerel was: • K2UO2(SO4)2 • Notice anything unusual about that formula? • Check out the center atom. • What do we know about that element?

32. Radioactivity! • So what did this have to do with X-rays or fluorescent materials? • Nothing! • Except that without those experiments, radioactivity would not have been discovered so early.