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A radioactive element decays by `beta-emission`. A detector records `n` beta particles in `2 s` and in next `2 s` it records `0.75 n` beta particles. Find mean life correct to nearest whole number. Given ln `|2| = 0.6931`, ln `|3|=1.0986`.A. `17s`B. `7s`C. `5s`D. `15s` |
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Answer» Correct Answer - B Let `N_(0)=` initial number of nuclei `n = N_(0) - N_(0)e^(-lambda xx)` `1.75 n = N_(0) - N_(0)e^(-4lambda)` `(1)/(1.75) = (1-e^(-2lambda))/(1-e^(-4lambda))` `1+e^(-2lambda) = 1.75` `e^(2lambda) = (1)/(0.75) = 1.33` `2 lambda = ln (1.33)` `tau = (1)/(lambda) = (2)/(ln(1.33)) = 7s` |
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