A radioactive material has mean lives of 1620 yr and 520 yr for `alphaandbeta-"emission"`, respectively. The material decays by simultaneous `alphaand

Monjur Alahi

A radioactive material has mean lives of 1620 yr and 520 yr for `alphaandbeta-"emission"`, respectively. The material decays by simultaneous `alphaandbeta-"emissions`. The time in which 1/4th of the material remains intact is
A. 4.675 yr
B. 7.20 yr
C. 5.45 yr
D. 324 yr


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Salim Ahmed Kawsar

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Correct Answer - C
`lamda=(lamda_(1)+lamda_(2))=(1)/(1620)+(1)/(520)=2.54xx10^(-3)yr^(-1)`
`therefore" " t_(1//2)=(1n(2))/(lamda)=272.8 yr`
(1/4) th of the material remainsintact after 2 half-lives.

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