Q21 of 106 Page 384

Radioactive 131I has a half-life of 8.0 days. A sample containing 131I has activity 20 μ Ci at t = 0.

(a) What is its activity at t = 4.0 days?


(b) What is its decay constant at t = 4.0 days?


Given,

Half-life = 8 days, A0 = 20μCi


a) We know that,




Where,


A= Activity of the substance


A0 = Initial activity


t = time


λ = decay constant


So,







b) Decay constant in per second s-1



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