Question

The activity of a sample drops by a factor of 3.0 in 8.9 minutes.

What is its half-life?

Answer 1

Given

      N /N_o =1/ 3

   time t = 8.9min

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   we know that

          N =N_o e^-?t

  

       1/3 =e^-?t     -------------(1)

      decay constant is

      ? = 0.693 / T_1/2

substitute the ? value in eq (1)

      1/3= e^{-[0.693 / T _1/2]t}

   solve T_1/2