Department of Pre-University Education, Karnataka course PUC Karnataka Science Class 12
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# A Certain Sample of a Radioactive Material Decays at the Rate of 500 per Second at a Certain Time. the Count Rate Falls to 200 per Second After 50 Minutes. - Physics

#### Question

A certain sample of a radioactive material decays at the rate of 500 per second at a certain time. The count rate falls to 200 per second after 50 minutes. (a) What is the decay constant of the sample? (b) What is its half-life?

#### Solution

Given:-
Initial rate of decay, A0 = 500,
Rate of decay after 50 minutes, A = 200
Time, t = 50 min
= 50 × 60
= 3000 s

(a)
Activity, A = A0e−λt
Here,  lambda = Disintegration constant

therefore 200 = 500 xx e^(-50 xx 60 xx lambda)

⇒ 2/5 = e^(-3000lambda)

⇒ "In"  2/5 = -3000lambda

⇒ lambda = 3.05 xx 10^-4  "s"^-1

(b)

Half - life, T_"1/2" = 0.693/lambda

= 2272.13  "s"

= 38 min

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#### APPEARS IN

Solution A Certain Sample of a Radioactive Material Decays at the Rate of 500 per Second at a Certain Time. the Count Rate Falls to 200 per Second After 50 Minutes. Concept: Radioactivity - Introduction of Radioactivity.
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