Radioactivity in a nutshell

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IGCSE Radioactivity in a nutshell
1. The results of Geiger and Marsden's `alpha particle scattering from gold foil'
experiment led to the realisation that atoms have a very small nucleus of positive
charge (Rutherford's nuclear model ) which accounts for the very large deflections
experienced by some alpha particles
2. Charge and speed affect the deflection of alpha particles by a nucleus, the greater
the charge the greater the deflection, the faster the speed the less the deflection
3. Unstable nuclei break up-decay and emit alpha, beta or gamma radiation. Alpha
particles are positive helium nuclei, beta particles are negative fast moving
electrons, gamma is neutral electromagnetic radiation
4. Nuclei are represented by symbol, atomic number, Z and mass number, M Z S
5. Isotopes have the same number of protons, different numbers of neutrons
6. Alpha radiation is strongly ionising and easily stopped by paper or a few cm of air,
beta radiation is less ionising and is stopped by a few cm of aluminium or 1m of air,
gamma radiation is weakly ionising and is stopped by lead.
7. Ionising radiations can be detected using a photographic film or a Geiger-Muller
8. The activity of a radioactive source decreases over a period of time and is
measured in becquerels
9. The term `half-life' means the time taken for half of the radioactive nuclei to decay
or for the activity to halve. Understand that half life s different for different
radioactive isotopes
10. Alpha radiation is used for smoke alarms, beta radiation is used for controlling the
thickness of lead sheets, gamma radiation is used for radiotherapy to kill tumours
or for taking gamma photographs if injected into the body. NB gamma is the only
radiation that can pass into or out of the body
11. We are always exposed to background radiation from rocks, sky, food, cosmic rays
12. The dangers of ionising radiations are that radiation can cause mutations in living
organisms and can damage cells and tissue
13. Nuclear fission is the splitting of a large nucleus eg uranium into 2 smaller daughter
nuclei ( fission fragments) with the additional emission of free neutrons
14. The free neutrons are very fast so need to be slowed down by collisions in a
graphite moderator before they can trigger more fissions
15. A chain reaction of fissions will continue if the uranium fuel is above a critical mass
as neutron produced by previous fissions strike more nuclei an cause more fissions
16. Control rods are used to absorb neutrons to control the rate of fission
17. Outline the stages in a nuclear power station and appreciate the concern over the
safe disposal of nuclear waste


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