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The half lives of a radioactive sample are 30 years and 60 years from `alpha`- emission and `beta`- emission respectively If the sample decays both by alpha-emission and `beta`-emission simultaneously, the time after which, only one-fourth of the sample remain isA. 10 yearsB. 20 yearsC. 40 yearsD. 45 years |
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Answer» Correct Answer - C `lambda_(1)=1/30` `lambda_(2)=1/60` `lambda=lambda_(1)+lambda_(2)` `lambda=1/20` `N=(N_(0))/(2^(t)//t^(1//2))` `N_(0)/4 = (N_(0))/((2)^(t//t^(1//2)))` `:. t=2t_(1//2)=2xx(0.693)/lambda` `t=2xx0.693xx20yrs` `=27.72yrs` |
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