JEE Main & Advanced Physics Nuclear Physics And Radioactivity Question Bank Self Evaluation Test - Nuclei

  • question_answer
    A nucleus at rest undergoes a decay emitting an \[\alpha -\]particle of de-Broglie wavelength \[\lambda =5.76\times {{10}^{-15}}m.\] If the mass of the daughter nucleus is \[223.610\] amu and that of the \[\alpha -\]particle is \[4.002\,amu,\] determine the mass of the parent nucleus inamu. \[(1\,amu=931.470\,\,MeV/{{c}^{2}}].\]

    A)  \[227.62\,\,amu\]

    B)  \[112.11\,\,amu\]

    C)  \[90.3\,\,amu\]

    D)  \[23.8\,\,amu\]

    Correct Answer: A

    Solution :

    [a] By conservation of momentum, we have \[0={{\vec{P}}_{\alpha }}+{{\vec{P}}_{d}}\Rightarrow {{\vec{P}}_{\alpha }}=-{{\vec{P}}_{d}}\]  or  \[{{P}_{\alpha }}={{P}_{d}}=P\] The kinetic energy released in the process \[K={{K}_{\alpha }}+{{K}_{p}}=\frac{{{P}^{2}}}{2{{m}_{\alpha }}}+\frac{{{P}^{2}}}{2{{m}_{d}}}\] \[=\frac{{{P}^{2}}}{2{{m}_{\alpha }}}\left( 1+\frac{{{m}_{\alpha }}}{{{m}_{d}}} \right)=\frac{{{(h/\lambda )}^{2}}}{2{{m}_{\alpha }}}\left( 1+\frac{{{m}_{\alpha }}}{{{m}_{d}}} \right)\] After substituting the given values, we get \[K=6.25\,\,MeV\] If \[{{m}_{P}}\] is the mass of the parent nucleus, then                         \[K+({{m}_{\alpha }}+{{m}_{d}}){{c}^{2}}={{m}_{p}}{{c}^{2}}\] or  \[6.25+(223.61+4.002){{c}^{2}}={{m}_{p}}{{c}^{2}}\] After simplifying, we get   \[{{m}_{p}}=227.62\] amu.


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