NEET Sample Paper NEET Sample Test Paper-50

  • question_answer 30) A freshly prepared radioactive source of half- life 2 hours emits radiation of intensity which is 64 times the permissible safe level. The minimum time after which it would be possible to work safely with the source is:

    A) 6 hours             

    B) 12 hours

    C) 24 hours                       

    D) 128 hours

    Correct Answer: B

    Solution :

    \[\frac{A}{{{A}_{0}}}=\frac{N}{{{N}_{0}}}\] Let safe-level activity be A. Initial activity = 64 A. Hence, \[\frac{N}{{{N}_{0}}}=\frac{A}{{{A}_{0}}}=\frac{A}{64A}\,\,=\,\,\frac{1}{64}\] \[{{\left( \frac{1}{2} \right)}^{n}}\,=\,\frac{1}{64}\,\,or\,\,n=6\] Hence, \[\frac{t}{T}=n=6\] But \[T\,\,=\,\,2\] hours,

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