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A sample of ._(38)^(90)Sr has an activity of 0.5 mCi. What is its specific activity? (t_(1//2) of ._(38)^(90)Sr = 19.9 years)

Answer»

SOLUTION :Rate of disintegrations `= LAMBDA xx` No. atoms
So, No of atoms
`= (0.5 xx 3.7 xx 10^(7))/(0.693) xx 19.9 xx 365 xx 24 xx 60 xx 60`
`= 1.675 xx 10^(16)`
Mass = `(90 xx 1.675 xx 10^(13))/(6.023 xx 10^(23)) = 2.50 xx 10^(-6) g`
Specific activity `= (0.5 xx 3.7 xx 10^(7))/(2.5 xx 10^(-6)) = 7.4 xx 10^(12) "DIS" g^(-1) s^(-1)`


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