1. Do now!
Can you read the last powerpoints that Mr Porter gave you?

2. ½ - life This is the time it takes half the nuclei to decay
Number of nuclei undecayed
A graph of the count rate against time will be the same shape
time
half-life (t½)

3. Different ½ - lives Different isotopes have different half-lives
The ½-life could be a few milliseconds or 5000 million years!
Number of nuclei undecayed
time
half-life (t½)

4. Questions!
Homework
Can you finish questions 1,2 and 3 that Mr Porter gave you last lesson AND do the questions on page 259 of your textbook. Due next Tuesday 24th November

5. Biomass, tidal, solar, hydroelectric, wave, coal, oil, wind.
Do now!
In pairs, can you decide which of the following energy sources is the odd one out?
Biomass, tidal, solar, hydroelectric, wave, coal, oil, wind.

6. Biomass, tidal, solar, hydroelectric, wave, coal, oil, wind.
Do now!
In pairs, can you decide which of the following energy sources is the odd one out?
Biomass, tidal, solar, hydroelectric, wave, coal, oil, wind.

7. Nuclear Physics

8. How do we know the structure of the atom?

9. The famous Geiger-Marsden Alpha scattering experiment
In 1909, Geiger and Marsden were studying how alpha particles are scattered by a thin gold foil.
Thin gold foil
Alpha source

10. Geiger-Marsden
As expected, most alpha particles were detected at very small scattering angles
Thin gold foil
Small-angle scattering
Alpha particles

11. Geiger-Marsden
To their great surprise, they found that some alpha particles (1 in ) had very large scattering angles
Thin gold foil
Small-angle scattering
Alpha particles
Large-angle scattering

12. Can you QUICKLY, quietly and sensibly follow Mr Porter?

13. Explaining Geiger and Marsdens’ results
The results suggested that the positive (repulsive) charge must be concentrated at the centre of the atom. Most alpha particles do not pass close to this so pass undisturbed, only alpha particles passing very close to this small nucleus get repelled backwards (the nucleus must also be very massive for this to happen).
nucleus

14. Rutherford did the calculations!
Rutherford (their supervisor) calculated theoretically that the atomic nucleus was confined to a diameter of about metres. That’s times smaller than the size of an atom (about metres).

15. Rutherford did the calculations!
If the nucleus of an atom was a ping-pong ball, the atom would be the size of a football stadium (and mostly full of nothing)!
Nucleus (ping-pong ball

16. Nuclear Fission

17. Uranium
Uranium 235 has a large unstable nucleus.
                                                                 

18. Capture
A lone neutron hitting the nucleus can be captured by the nucleus, forming Uranium 236.

19. Capture
A lone neutron hitting the nucleus can be captured by the nucleus, forming Uranium 236.

20. Fission
The Uranium 236 is very unstable and splits into two smaller nuclei (this is called nuclear fission)

21. Fission
The Uranium 236 is very unstable and splits into two smaller nuclei (this is called nuclear fission)

22. Free neutrons
As well as the two smaller nuclei (called daughter nuclei), three neutrons are released (with lots of kinetic energy)

23. Fission
These free neutrons can strike more uranium nuclei, causing them to split.

24. Chain Reaction
If there is enough uranium (critical mass) a chain reaction occurs. Huge amounts of energy are released very quickly.
                                                                 
                                                                 

25. Chain Reaction
If there is enough uranium (critical mass) a chain reaction occurs. Huge amounts of energy are released very quickly.
                                                                 
                                                                 
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26. Bang!
This can result in a nuclear explosion!YouTube - nuclear bomb 4

28. Controlled fission
The chain reaction can be controlled using control rods and a moderator. The energy can then be used (normally to generate electricity).

29. Moderator
This slows the free neutrons down, making them easier to absorb by the uranium 235 nuclei. Graphite or water is normally used.

30. Control rods
These absorb excess neutrons,making sure that the reaction does not get out of control. Boron is normally used.

31. Heat
The moderator gets hot from the energy it absorbs from the neutrons.

32. Heat
This heat is used to heat water, to make steam, which turns a turbine, which turns a generator, which makes electricity.

33. Nuclear Power
That’s how a nuclear power station works!

34. Let’s try some questions.
Can you now read pages 260 and 261 and mind-map fission and nuclear power

36. Let’s try some questions.
Can you READ pages 264 and 265 of the book?

37. Used as Tracers

38. Used as Tracers

39. Used as Tracers

40. Killing microbes

41. Killing microbes

42. Thickness control

43. Thickness control

44. Smoke detection

45. Checking welds

46. Radioactive dating

47. Summary sheet

48. Can you answer the questions on pages 261 and 265?