Department of Pre-University Education, Karnataka course PUC Karnataka Science Class 12
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# The Count Rate from a Radioactive Sample Falls from 4.0 × 106 per Second to 1.0 × 106per Second in 20 Hours. What Will Be the Count Rate 100 Hours After the Beginning? - Physics

#### Question

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

#### Solution

Given:-

Initial count rate of radioactive sample, A0 = 4 × 106 disintegration/sec

Count rate of radioactive sample after 20 hours, A = 1 × 106 disintegration/sec

Time, t = 20 hours

Activity of radioactive sample (A) is given by

A = A_0/2^(t/(T"/"2)

Here , T_"1/2" = Half - life period

On substituting the values of A_0 and A , we have

2^(t/(T"/"2) = 2^2

⇒ t/(T"/"2) = 2

⇒ T"/"2 = t"/"2 = 20  "h""/"2 = 10 "h"

100 hours after the beginning,

Count rate , A" = A_0/2^(t/(T/2)

⇒ A" = (4 xx 10^6)/(2^(100/10))

= 0.390625 xx 10^4

= 3.9 xx 10^3 " disintegrations/sec"

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#### APPEARS IN

Solution The Count Rate from a Radioactive Sample Falls from 4.0 × 106 per Second to 1.0 × 106per Second in 20 Hours. What Will Be the Count Rate 100 Hours After the Beginning? Concept: Radioactivity - Introduction of Radioactivity.
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