Modern Physics 3 Question 35

36. A radioactive element decays by β-emission. A detector records n beta particles in 2s and in next 2s it records 0.75n beta particles. Find mean life correct to nearest whole number. Given ln|2|=0.6931,ln|3|=1.0986.

(2003, 2M)

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Solution:

  1. Let n0 be the number of radioactive nuclei at time t=0. Number of nuclei decayed in time t are given by n0(1eλt), which is also equal to the number of beta particles emitted during the same interval of time. For the given condition,

n=n0(1e2λ)(n+0.75n)=n0(1e4λ)

Dividing Eq. (ii) by (i), we get

$$



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