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  • A radioactive material has mean lives of 1620 yr and 520 yr for  and  -emission, respective

A radioactive material has mean lives of 1620 yr and 520 yr for \alpha and \beta -emission, respectively. The material
decays by simultaneous \alpha and \beta -emission. The time in which \mathrm{1/4^{th} } of the material remains intact is

Option: 1

4675 yr


Option: 2

720 yr


Option: 3

545 yr


Option: 4

324 yr


Answers (1)

best_answer

\lambda=\left(\lambda_1+\lambda_2\right)=\frac{1}{1620}+\frac{1}{520}=2.54 \times 10^{-3} \mathrm{yr}^{-1}

\therefore \quad \mathrm{t}_{1 / 2}=\frac{\ln (2)}{\lambda}=272.8 \mathrm{yr}

(1/4)th of the material remains intact after 2 half-lives.

Posted by

Shailly goel

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