gamma - very weakly ionising, travels at the speed of light, very penetrating.
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where does background radiation come from?
Radon gas released from rocks emits alpha radiation
ground and buildings: all rock contains radioactive isotopes
cosmic rays
living things: plants and animals all contain carbon, some of which is radioactive carbon 14
man-made radiation: makes up a very small portionof background radiation.
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Uses of radioactive isotopes
Radiocarbon dating (carbon-14)
diagnose and treat medical problems
sterilise food
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Half-life and rate of decay
Activity (number of atoms which decay each second) is proportional to the size of a sample.
decay constant (lambda) measures how quickly an isotope will decay.
bigger decay constant = faster rate of decay
Half-life: the average time it takes for the number of undecayed atoms to halve.(in practice it is measured by the time taken for the activity to halve)
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Fission reactors
U-235 hit by thermal neutron
neutron absorbed
unstable U-236 breaks up into two smaller nuclei and some high speed neutrons
difference in binding energy is given off as Ek of daughter products
harnessed to drive electricity generating system
graphite/water moderator slows emitted neutrons
they arrive at next fuel rod at slow enough speed to be absorbed
cadmium/boron control rods absorb excess neutrons and prevent reaction running out of control
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