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The half-life of .(38)^(90)Sr is 20 year...

The half-life of `._(38)^(90)Sr` is 20 years. If its sample having initial activity of 800 dis/min is taken, what would be its activity after 80 years

A

500 dis/min

B

800 dis/min

C

1000 dis/min

D

1600 dis/min

Text Solution

Verified by Experts

The correct Answer is:
A
`(-dN)/(dt) prop N`
So, `((-dN)/(dt))_(80)//((-dN)/(dt))_("initial") = (N_(80))/(N_0)`
n = 80/ 20 = 4
`(N_(80))/(N_0) = (1/2)^n = (1/2)^4 = 1/(16)`
`((-dN)/(dt))_(80)//8000 = 1/(16)`
= 500 dis/min
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