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If 1.0 mg of cesium-137 decays over a period of 90 years how many mg of cesium-137 would remain?
Wiki User
∙ 15y ago
Since the half-life of cesium-137 is about 30 years, 3 half-lives would have passed in 90 years. The first half-life would leave .5 mg of cesium-137. The second would leave .25 mg, and the third half-life would leave .175 mg of cesium-137.
Wiki User
∙ 15y ago
Wiki User
∙ 15y ago1/8th of a gram.
You compute it like this: After 30 years, half of the original amount would remain (1/2-gram). After another 30 years, half of that half would remain (1/4-gram). After the remaining 30 years, half of the 1/4-gram would remain, or 1/8-gram.
Wikipedia has a simple table and explanation as well:
http://en.wikipedia.org/wiki/Half-life
Wiki User
∙ 13y ago0.25 mg
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