Question

A human body excretes certain material by a law similar to radioactivity. The body excretes half the amount injected in $24$ $h$. Find the time in which activity falls to $3\mu$ $Ci$. If a person is injected technitium ($t_{1/2}$= $6h$) and its activity just after the injection is $6\mu$ $Ci$

• A. $4.8$ $h$
• B. $6$ $h$
• C. $6.3$ $h$
• D. none of these

Answer 1

Answer: (A)

$4.8$ $h$

$\frac{1}{t}$ $=\frac{1}{t_1}+\frac{1}{t_2}$
$t$ $=\frac{t_1{t}_2}{t_2+t_2}$
$=\frac{24\times 6}{24+6}$ $=4.8$ $h$