Nuclear Physics And Radioactivity Question 63
Question: A radioactive material decays by simultaneous emission of two particles with respective half lives 1620 and 810 years. The time (in years) after which one- fourth of the material remains is [IIT 1995; UPSEAT 2002]
Options:
A) 1080
B) 2430
C) 3240
D) 4860
Show Answer
Answer:
Correct Answer: A
Solution:
$ \lambda ={\lambda_{1}}+{\lambda_{2}}\Rightarrow \frac{1}{T}=\frac{1}{T_{1}}+\frac{1}{T_{2}} $
$ \therefore T=\frac{T_{1}T_{2}}{T_{1}+T_{2}}=\frac{810\times 1620}{810+1620}=540\ years $ Hence $ \frac{1}{4} $ th of material remain after 1080 years.
BETA
