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: The [[Count Rate|count rate]] of a sample of [[Unstable Isotope|unstable isotope]] can be predicted given its initial [[Count Rate|count rate]], its '''half life''' and the [[time]] it has been given.
===Finding Half Life and Count Rate===
{| class="wikitable"
| style="height:20px; width:100px; text-align:center;" |Time /s
| style="height:20px; width:50px; text-align:center;" |62
|}
The '''half life''' of of this [[sample]] of [[radioactive]] [[isotope]] can be found by halving the initial count rate.
1000/2 = 500Bq
The [[isotope]] took 20 seconds to half in [[Count Rate|count rate]] so the '''half life''' is 20 [[seconds]].
The [[Count Rate|count rate]] at 90 seconds can be predicted. Since the '''half life''' is 20 seconds the [[Count Rate|count rate]] 20 seconds earlier can be halved. At 70 seconds the [[Count Rate|count rate]] was 88Bq. Therefore at 90 seconds the [[Count Rate|count rate]] would be:
88/2 = 44Bq
The [[Count Rate|count rate]] at 10 seconds before the sample was first tested can also be predicted. Since the '''half life''' is 20 seconds the [[Count Rate|count rate]] 20 seconds later can be doubled. At 10 seconds the [[Count Rate|count rate]] was 707Bq. Therefore at -10 seconds the [[Count Rate|count rate]] would have been:
707x2= 1414Bq