High School

Cesium-137 was a radioactive chemical released at the Chernobyl nuclear reactor in April 1986. The estimated amount of Cesium-137 released was 3980 grams. The half-life of cesium-137 is 30.22 years. How long will it take for 31.09 grams to remain in the environment?

Answer :

First, find how many half lives Cesium-137 goes through (i.e. how many times it splits in half to get from 3980g to 31.09g

3980 --> 1990 --> 995 -->497.5 --> 248.75 -->124.375-->62.175--> 31.09375

In this case, there are 7 half lives (counted by the number of arrows) for Cesium -137 to get to 31.09

7 half lives x 30.22 years = 211.54 years

Since the cesium is split in half 7 times to get to 31.09, multiply the half life by 7 to get around 211.54 years.

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