Question

The half-life of Plutonium-239 is 24 300 years. If 8 kilograms of this isotope is stored, how many years would pass before the radiation is 1/8 of the initial amount?
a 48 600 years
b 12 200 years
c 24 300 years
d 72 900 years

Answer 1

Each half life is 1/2 of original amount, so this would take 3 half-lives because (1/2 * 1/2 * 1/2 = 1/8)

Total time = 24,300 * 3 = 72,900 years

Answer 2

24,300 per half life. 
So 1/8 = 1/2 * 1/2 * 1/2
This is 3 halflifes. 
24,300 * 3 = 72,900 years.

Your answer is D.


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