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Q30PE
Expert-verifiedA generation is about one-third of a lifetime. Approximately how many generations have passed since the year \({\bf{0}}\) AD?
The required number of generations have passed since the year \(0\) AD is \(95\).
The time taken by the sample to decay to half the original number of the nuclei is called the half-life of the sample.
The expression of the half-life of a radioactive isotope is given as follows.
\({t_{{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\\}
\!\lower0.7ex\hbox{$2$}}}} = \frac{{0.693}}{\lambda }\)
Here, \(\lambda \) is the activity of the sample.
The half-life of the time is in the order as,
\({T_{{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\\}
\!\lower0.7ex\hbox{$2$}}}} = {10^9}{\rm{ }}s\)
The half-life of the a generation is twice the half-life.
\(\begin{aligned}{c}1{\rm{ }}life - time &= 2\left( {{T_{{1 \mathord{\left/ {\vphantom {1 2}} \right.\\} 2}}}} \right)\\ &= 2\left( {{{10}^9}{\rm{ }}s} \right)\end{aligned}\)
The time elapsed since \(0{\rm{ }}AD\) is \(2019\) years. The expression for the number of generations passed is,
\(Number{\rm{ }}of{\rm{ generations}} = \frac{{2019}}{{\frac{1}{3} \times life{\rm{ }}time}}\)
Substitute \(2\left( {{{10}^9}{\rm{ }}s} \right)\) for \(1{\rm{ }}life - time\) in the above equation.
\(\begin{aligned}{c}Number{\rm{ }}of{\rm{ generations}} &= \frac{{3 \times \left( {2019{\rm{ years}}} \right)\left( {\frac{{3.15 \times {{10}^9}{\rm{ }}s}}{{1{\rm{ }}year}}} \right)}}{{2\left( {{{10}^9}{\rm{ }}s} \right)}}\\ &= 95.39\\ \approx 95\end{aligned}\)
Hence, the required number of generations that have passed since the year \(0\) AD is \(95\).
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