Q2 / 97 · NTA Abhyas (JEE Main) 2020 · Physics · Nuclear Physics

In a sample initially, there are an equal number of atoms of two radioactive isotopes A and B. 3 days later, the number of atoms of A is twice that of B. The half-life of B is 1.5 days. What is the half-life (in days) of isotope A?

Correct answer: 3

Solution

         ABt=0          N0N0t0=3 days       2NN
2N=N0(0.5)t0/τ1
N=N0(0.5)t0/τ2
2=(0.5)t0(1τ1−1τ2)
0.5−1=(0.5)3τ1−2
⇒-1=3τ1-2                  ∴τ1=3 days 

Hence, the correct answer is 3.

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