SOLUTION: The half life of cobalt-60 is 5.3 years. a) Find its decay rate. b) If you initially have 20 grams of this material, how long until only 15 grams remain?

Question 625285: The half life of cobalt-60 is 5.3 years.
a) Find its decay rate.
b) If you initially have 20 grams of this material, how long until only 15
grams remain?
Answer by nerdybill(7384) (Show Source): You can put this solution on YOUR website!
The half life of cobalt-60 is 5.3 years.
a) Find its decay rate.
1/2 = e^(5.3r)
ln(1/2) = 5.3r
ln(1/2)/5.3 = r
-.1308 = r
b) If you initially have 20 grams of this material, how long until only 15
grams remain?
15 = 20e^(-.1308t)
15/20 = e^(-.1308t)
3/4 = e^(-.1308t)
ln(3/4) = -.1308t
ln(3/4)/(-.1308) = t
2.2 years = t
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