The Chernobyl reactor accident in what is now Ukraine was the worst nuclear disa
ID: 1389770 • Letter: T
Question
The Chernobyl reactor accident in what is now Ukraine was the worst nuclear disaster of all time. Fission products from the reactor core spread over a wide area. The primary radiation exposure to people in western Europe was due to the short-lived (half-life 8.0 days) isotope 131I, which fell across the landscape and was ingested by grazing cows that concentrated the isotope in their milk. Farmers couldn't sell the contaminated milk, so many opted to use the milk to make cheese, aging it until the radioactivity decayed to acceptable levels.
How much time must elapse for the activity of a block of cheese containing 131I to drop to 1.0% of its initial value?
(Express your answer to two significant figures and include the appropriate units.)
Explanation / Answer
... An = Ao (1/2)^(time/halflife)
I assume the "1.0" means 1%
... .01 = (1/2)^(time/8)
or ln(.01) = (time/8) ln(.5)
or time = 8 ln(.01)/ln(.5)
or time = 53.150849518 days