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13.Nuclei
medium
If one starts with one curie of radioactive substance ($T_{1/2} = 12\,hrs$) the activity left after a period of $1$ week will be about
A
$1\, curie$
B
$120 \,micro \,curie$
C
$60\, micro \,curie$
D
$8\, mili \,curie$
Solution
(c) $1$ week $\approx 7 \, days \simeq 7 × 24\, hrs \simeq 14\,$ half lives
Number of atoms left $ = \frac{{No}}{{{{(2)}^{14}}}}$, Activity =$N\lambda $
$\therefore$ Activity left is $\frac{1}{{{{(2)}^{14}}}}$ times the initial
==> $\frac{1}{{{{(2)}^{14}}}} \times 1$ curie .
$= \frac{1}{{16384}} \times 1$ curie$ \cong $ $61 \times {10^{ – 6}}$ curie
$ \approx 60\mu \, curie.$
Standard 12
Physics
