1. Radioactivity

2. History Henri Becquerel discovered radioactivity.
Left uranium salts in the dark on photographic paper and found that a reaction had occurred – could only have occurred naturally.
Won Nobel Prize in physics for it

4. Pierre & Marie Curie discovered a number of radioactive elements – polonium, germanium & radium
Marie won the Nobel Prize in chemistry for these discoveries
Pierre died before he could be awarded

5. Radioactivity
Radioactivity is the spontaneous breaking up of unstable nuclei with the emission of one or more types of radiation
Lots of natural radiation around us – called background radiation
Main source of background radiation in Ireland is from radon gas

7. Radioactive particles
3 types – alpha, beta & gamma
Alpha:
2 protons & 2 neutrons stuck together like a helium (He) nucleus
Positive charge
Low penetrating power
Stopped by sheet of paper
E.g., americium-241 used in smoke detectors

9. Beta: Neutron converted into a proton and an electron
Proton stays in nucleus and electron is emitted
Negative charge
More penetrating than alpha
Stopped by sheet of aluminium foil
E.g., carbon-14 used in carbon dating by archaeologists

11. Gamma: high energy electromagnetic rays No charge Most penetrating
Stopped by thick slab of lead
E.g., cobalt-60 used to kill cancer cells in radiotherapy treatment for cancer

14. Detection Geiger-Muller tube connected to a ratemeter
Switch it on and note the background radiation count
Using a tongs hold a radioactive sample up to the tube and note that the count rate increases

15. Place a suitable source for blocking the sample between it and the tube and note that the count rate falls
Repeat for different samples

16. Nuclear reactions
In a chemical reaction bonds are broken and new ones are formed
In a nuclear reaction radioactive radiation is emitted from a nucleus and a new element is formed

17. Emission of alpha particles:
Nucleus loses 2 protons and 2 neutrons
Mass number AND Atomic number decrease
New element formed
Po → _____ He

18. Emission of beta particles: - Nucleus loses a neutron but gains a
proton so mass number stays the same
- Atomic number increases
- New element formed
Na → _____ e
Bi → _____ e

19. Emission of gamma energy:
Energy is lost from the nucleus but no new element is formed
Usually accompanies emission of other radioactive particles
Changing of one element to another is called transmutation.

20. Radioisotopes & their uses
Radioactive isotopes are called radioisotopes
Uses:
Medical:
Gamma rays used in cancer treatment to kill cancer cells.
Gamma rays used to sterilise equipment.

21. Archaeological:
Carbon 14 dating used to age substances
Carbon consists of three isotopes, carbon-14 being radioactive
By comparing the ratio of radioactive to non-radioactive isotopes can calculate age

22. Agricultural:
Radioactive isotopes added to fertilisers to measure the uptake of the fertiliser
Farmers can measure amount of radioactivity in leaves of plants to see how far the fertiliser has travelled in the plant

23. Food irradiation:
Gamma rays sterilise food by killing off bacteria and mould which can spoil it
Not suitable for all foods, e.g., causes red meat to change colour and taste

24. Industrial: Test for leaks in pipes
Radioactive isotope added and followed until it can no longer be registered on Geiger-Muller counter
Spot where signal disappears is spot where leak is in pipe.

25. Half-life
Half-life of a radioactive element is the time taken for half the nuclei in a sample to decay
Use Geiger-Muller tube and ratemeter to measure it

26. Examples –
- Carbon-14 = 5,700 yrs
- Cobalt-60 = 5 yrs
- Polonium-234 = s

27. Half-life graph