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The half-life of a radioisotope is 20 ye...

The half-life of a radioisotope is 20 years. If the sample has an initial activity of 640 dps,than what will be its activity after 80 years?

A

20 dps

B

30 dps

C

40 dps

D

50 dps

Text Solution

Verified by Experts

The correct Answer is:
C
`t_(1//2) = 20 "years" , t = 80` years,
`N_0 = 640 dps, N_t = ?`
Number of half lives gone `(n) = (80/20) = 4`
Now, `N_t = N_0 xx (1/2)^(n) = 640 xx (1/2)^(4) = (640)/(16) = 40 dps`
The activity of the radioisotope will be 40 dps after 80 years.
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