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7b) Radioactivity part 2 (half life (the time taken for half of the…
7b) Radioactivity part 2
half life
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each time a decay happens and an alpha or beta particle or gamma ray is given out, it means one more nucleus has disappeared
as the unstable nuclei all disappear, the activity as a whole will decrease so the older a sample becomes, the less radiation it will emit
the problem with trying to measure this is that the activity never reaches zero, which is why we have to use the idea of half-life to measure how quickly the activity drops off
how quickly the activity drops off varies. Isotopes take a few hours before almost all the unstable nuclei have decayed, whilst others last millions of years
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long half life means the activity falls more slowly because most of the nuclei don't decay for a long time
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radioactive decay
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when the nucleus decays it releases one or more of the three types of radiation - alpha, gamma and beta
nuclei of unstable isotopes break down at random. If you have 1000 unstable nuclei, you couldn't say when any of them will decay and you can't make decay happen
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half life graphs
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half life is found by finding the time interval on the bottom axis corresponding to a halving of the on the vertical axis
measure the background activity first and then subtract it from every reading you get, before plotting the results on the graph
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calculating half life
the activity of a radioactive source is 640 Bq. Two hours later it has fallen to 40 Bq. Find the half life of this sample
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blocking radioactivity
alpha
blocked by paper, skin & a few cm of air
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