BCECE Medical BCECE Medical Solved Papers-2005

  • question_answer
    If half-life of radium is 77 days, its decay constant will be :

    A)  \[3\times {{10}^{-3}}\]/day   

    B)  \[9\times {{10}^{-3}}\]/day

    C)  \[1\times {{10}^{-3}}\]/day 

    D)  \[6\times {{10}^{-3}}\]/day

    Correct Answer: B

    Solution :

    The time required for the number of parent nuclei to fall to 50% is called half-life \[{{T}_{1/2}}\] and may be related to K as follows. Since,    \[0.5\,{{N}_{0}}={{N}_{0}}{{e}^{-{{T}_{1/2}}}}\] we have, \[\lambda {{T}_{1/2}}=\ln (2)=0.693\] or            \[{{T}_{1/2}}=\frac{0.693}{\lambda }\] or            \[\lambda =\frac{0.693}{{{T}_{1/2}}}\] Given,   \[{{T}_{1/2}}=77\] days \[\therefore \] \[\lambda =\frac{0.693}{77}=9\times {{10}^{-3}}/\] days


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