AMU Medical AMU Solved Paper-2004

  • question_answer
    The half-life of radium is 1620 yr and its atomic weight is 226 kg per kilomol. The number of atoms that will decay from its 1 g sample per second will be (Avogadros number \[\text{N}=\text{6}.0\text{23}\times \text{1}{{0}^{\text{23}}}\text{ atoms}/\text{ mol})\]

    A) \[\text{3}.\text{61}\times \text{l}{{0}^{\text{1}0}}\]                      

    B)  \[\text{3}.\text{61}\times \text{l}{{0}^{\text{12}}}\]

    C) \[\text{3}.\text{11}\times \text{l}{{0}^{\text{15}}}\]                      

    D)  \[\text{31}.\text{1}\times \text{l}{{0}^{\text{15}}}\]

    Correct Answer: A

    Solution :

                     From Rutherford Soddy law, the number of atoms that will decay is                 \[\frac{dN}{dt}=\lambda \,N\]                   ?. (i) Also,      \[\lambda =\frac{0.693}{{{T}_{1/2}}}\]                   .... (ii) where \[{{T}_{1/2}}\] is half-life of radioactive sample. Given,   \[{{T}_{1/2}}=1620\,yr\] ^1620^                 \[=1620\times 365\times 24\times 60\times 60\] \[\therefore \]  \[\lambda =\frac{0.693}{1620\times 365\times 24\times 60\times 60}\] and        \[N=\frac{6.023\times {{10}^{23}}}{226}\] Putting these values of N and \[\lambda \] in Eq. (i), we get \[\frac{dN}{dt}=\frac{0.693\times 6.023\times {{10}^{23}}}{1620\times 365\times 24\times 60\times 60\times 226}\] \[\frac{dN}{dt}=3.61\times {{10}^{10}}\]


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