1. Nuclear Physics

2. A short history
Aristotle emphasised that nature consisted of four elements: air, earth, fire, and water.
Atoms were initially proposed by John Dalton in the 1700’s.
J.J. Thomson held that atoms are uniform spheres of positively charged matter in which electrons are embedded like a plum pudding.(1800’s)
Rutherford established the presence of the nucleus(1911)

3. The Rutherford scattering Experiment
Results
The atom is mainly empty space.
There is a small centre of positive charge.
Results
The atom is mainly empty space.
There is a small centre of positive charge.

4. The Rutherford scattering Experiment
Positive alpha particles are targeted at thin gold foil.
Most pass through, a few are deflected.
Conclusion
The atom is mostly empty space.
The atom has a small centre of positive charge.

5. Explanation of how spectra are formed.
E=hf

6. Spectra When electrons are given energy they jump to a higher state.
The absorbed energy is released when they return to the ground state.
The greater the enegy jump the greater the frequency of the light.
This causes spectral colours.

7. Spectra
Absorption spectra- Certain wavelengths are absorbed from a continuous spectrum as it passes through a material.
Emission spectra- Specific wavelengths are emitted by a hot substance.
Types of spectra
Line spectra= hot gas
Continuous spectra= hot solids
Spectroscopy is the method of identifying elements by their spectrum.
Bunsen and Kirchoff discovered that no two elements emit the same spectrum.

9. Revision of some terms…..
The atomic number is the number of protons in the nucleus.(Z)
The mass number is the number of protons and neutrons in the nucleus.(A)
Isotopes are forms of the same atom that have different numbers of neutrons.

10. Radioactivity Discovered by Becquerel in 1896
It is the spontaneous disintegration of the nucleus by emission of one or more types of radiation.
There are 3 types of radiation which is proved experimentally by passing radiation through magnetic or electric fields.
Alpha, Beta and Gamma

11. To distinguish between the 3 types of radiation

12. Properties of alpha α or
Positive charge
Size of a Helium nucleus (2 protons and 2 neutrons)
Good ionisers
Poor penetrators
Alpha emission reduces the mass number by 4 and the atomic number by 2.

13. Properties of Beta β or Negative charge Medium ioniser.
Medium penetrator.
Beta emission increases the atomic number by one and the mass number remains unchanged. This is because a neutron forms a proton and an electron (beta)

14. Properties of gamma γ Electromagnetic radiation Good penetrator.
Poor ioniser.
Does not affect the mass or atomic numbers.

15. To demonstrate the ionizing affect of radioactivity
Procedure: Bring a radioactive source close to the cap of a charged Gold Leaf Electroscope.
Observation: Leaves collapse.
Conclusion: The charge on the electroscope became neutralised by the ionised air.

16. The Geiger Muller tube
Mica window
Counter
When radiation enters the detector it ionises the gas inside.
A voltage exists between the central axis and the cylinder wall.
Negative ions are attracted towards the positive anode and travel through the meter, registering a “count”.

17. To Measure background radiation
Note the count after 1 minute on the geiger counter.
Divide by 60 to find the activity in Becquerels.

18. The Penetrating power of alpha, Beta and gamma

19. To examine the penetrating power of the 3 types of radiation
Get the background count rate.
Place the alpha source in front of the detector and note the count rate.
Move the detector away from the source in small steps and calculate the average count rate at each step.
Continue until count rate equals background count rate.
Repeat for Beta source and Gamma source.
Note
We could also have tested the penetrative ability of the different sources by placing different materials between source and detector.
We would find that a few sheets of paper would stop Alpha, Aluminium would be required for Beta, while lead is necessary for Gamma radiation.
the activity. a sheet of paper in front of the source and note the activity. It is less.
Repeat putting a sheet of aluminium and then a block of lead.
In each case the activity drops as the alpha, beta and gamma radiations are stopped by the paper, aluminium and lead respectively.

20. Activity
The activity of a sample is the number of nuclei that decay per second. The unit of activity is the Becquerel.

21. The Law of Radioactive Decay
The activity of a sample is proportional to the number of nuclei present.
The Half Life
This is the time taken for the activity to decrease by half.

23. Half Life

24. The equations

25. Note after n half lives of the original sample remain.
A radioactive element has a half life of 5 years. What fraction of the sample will have decayed after 20 years?
Note after n half lives of the original sample remain.

26. The mole
A mole of any substance is the amount of the substance that contains as many particles as there are atoms in 12g of carbon 12. The atomic mass of any element expressed in grams contains 6.02X1023 atoms.

27. To examine the ionisation caused by nuclear radiation
Charge an electroscope. Bring the radioactive source close to the cap. The leaves collapse as the ions neutralise the charge on the electroscope.
Radioactive source

28. Nuclear Fission
Fission is the splitting of a large nucleus with the release of energy.
Uranium-235 is a fissile element.

29. Chain Reaction Each U-235 produces 3 neutrons when it splits.
For a chain reaction to occur each fission must produce further fission.
To achieve this Uranium enriched with U-235 is used.

30. The Fission Reactor Boron Graphite Uranium Concrete
Graphite or heavy water.

31. The Fission Reactor
Control rods absorb neutrons and so control the reaction
The moderator slows the neutrons (thermal neutrons) to allow them to be absorbed by U235
The fuel is Uranium enriched with U235

32. Conservation of Mass Energy
Einstein proposed that mass and energy were simply different ways of looking at the same thing.
Mass can turn to energy and vice versa.
He proposed that the amount of energy created from mass is found using the formula E = mc2
1g of matter was converted to energy in the nuclear bomb that exploded in Hiroshima in 1945

33. Environmental impact
Mining Uranium releases Radon gas into the atmosphere
Radioactive waste
Accidents-Chernobyl and Fukushima
Nuclear reprocessing-transport of spent rods

34. AND THIS ……..

35. Nuclear Fusion
This is the joining of two small nuclei to form a larger nucleus with the release of energy.

36. Fusion
Advantages
There is a lot more energy released during fusion than fission
Hardly any waste produced
Disadvantages
Fusion will only occur at temperatures of million Kelvin
Not currently profitable

37. Fusion powers the sun

38. Uses of Radioisotopes Medical imaging Medical therapy Food irradiation
Carbon dating
Smoke detectors
Checking material thickness