Question

A piece of wood collected from Cro Magnon caves gave $4dpm$. A freshly cut wood of the same weight gives $16dpm$. The cro magnon man lived about $\underset{–}{}$ years ago
(Half life of C${}^{14}$ is $5760$ years. Assume the activity is due to C${}^{14}$ only)

• A. $5700$
• B. $2900$
• C. $11520$
• D. $1400$

Answer 1

Answer: (C)

$11520$

Activity of freshly cut wood $=16dpm$
Activity of wood from cave $=4dpm$
Let the no of half lives needed to decrease radioactivity from 16 dpm to 4 dpm be x,
$4=\frac{16}{2^x}\Rightarrow x=2$

Time taken $=2$ half lives
$=2\times 5760years$
$=11520years$