Half-Life

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What happens to radioactivity over time?
Over time, the activity of a radioactive source decreases.
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What happens when a nucleus decays?
Each time a radioactive nucleus decays and radiation is emitted, one more radioactive nucleus disappears.
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As each nucleus disappears, what does this cause?
As the unstable nuclei steadily disappear, the activity as a whole will disappear. So, the older the a source becomes, the less radiation it will emit.
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How can this be measured?
The activity never reaches zero, so we have to use half life to work out how quickly the activity drops out.
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So, what is half life?
Half life is the time taken for half of the undecayed nuclei to decay.
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What is half life measured in?
Half life is measured in becquerels. 1 Bq is 1 decay per second. This can be measured by a geiger-muller tube.
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Example: The activity is 640 Bq and falls to 40 Bq in two hours. What is the half life of this sample?
You would divide 640 by two to find out what it is after one half life. You would keep doing this until you got down to 40, which is in this case after 4 half lives. So two hours represents 4 half-lives, so the half life is 30 minutes.
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How can half life be shown on a graph?
The half life is found from the graph by finding the time interval on the bottom axis, corresponding to a halving of the activity on the vertical axis. Remember to work out the background radiation and to subtract it from your readings.
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How can radioactive substances be disposed of?
Normally it's by vitrification - they melt the waste with other materials to form glass and the liquid glass is stored in steel canisters and buried deep underground.
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What is another way?
Another way to deal with nuclear waste is to pack it into thick metal containers and bury it in a deep hole filled with lots of concrete. The point is to create a barrier to absorb the radiation before it reaches the earth's surface.
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Other cards in this set

Card 2

Front

What happens when a nucleus decays?

Back

Each time a radioactive nucleus decays and radiation is emitted, one more radioactive nucleus disappears.

Card 3

Front

As each nucleus disappears, what does this cause?

Back

Preview of the front of card 3

Card 4

Front

How can this be measured?

Back

Preview of the front of card 4

Card 5

Front

So, what is half life?

Back

Preview of the front of card 5
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