The count rate from a radioactive sample falls from 4.0 × 106 per second to 1.0 × 106 per second in 20 hours. What will be the count rate 100 hours after the beginning?

We know that,



Where,


A= Activity of the substance=1 × 106 s-1


A0 = Initial activity=4 × 106 s-1


t = time=20h


λ = decay constant


So according to the problem,




Now we have to evaluate activity after 100 hours





A = 3.9× 103 disintegrations per second


Hence, the activity after 100 hours is 3.9× 103 disintegrations per second.


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