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Hot goIITian

Joined:	29 Mar 2012
Post:	158

24 Apr 2012 22:09:17 IST

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nuclear

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a radioactive isotope X of half life of 1.37 X 10^ 9 yrs decays to Y which is stable. a sample of rocks frm moon ws found to contain both X & Y in the ratio 1:7 . the age of rock is ? ans is 4.11 X 10^ 9 yrs .hw?

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souradipta

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Joined: 21 Apr 2012

Posts: 57

24 Apr 2012 22:42:58 IST

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thus t=3x1.37x10^9 yrs=4.11x10^9

edison

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Joined: 19 Oct 2006

Posts: 7797

26 Apr 2012 10:49:24 IST

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Using the expression

$N_A = N_{A0}e^{-{\lambda}t} \,\!$

λ = 0.693 / t1/2

or λ = 0.693 / (1.37 X 10⁹)

or λ = 5.05 x 10^-10

N_A / N_A0 = 1/8 = exp (-5.05 x 10^-10t)

so t = 4.11 x 10^-9 yrs

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