The decay constant of 238U is 4.9 × 10–18 s–1.

(a) What is the average-life of 238U?


(b) What is the half-life of 238U?


(c) By what factor does the activity of a 238U sample decrease in 9 × 109 years?


Given,

The decay constant of 238U is 4.9 × 10–18 s–1


a) Average life




b) Half life




c) 9 × 109 years = 2 half-lives(approximately)


We know



where A= Activity of the substance


A0 = Initial activity


N = number of half lives


N = 2, in this case.


So it is evident that the sample activity will decrease by a factor of 4


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