Question

A sample of ${}^{14}C{O}_2$ was to be mixed with ordinary $C{O}_2$ for a biological tracer experiment. In order that 10 $c{m}^3$ of diluted gas should have ${10}^4$ dis / min, what activity ( in $\mu Ci$ ) of radioactive carbon is needed to prepare 60 L of diluted gas at STP.

• A. $270\mu Ci$
• B. $27\mu Ci$
• C. $2.7\mu Ci$
• D. $2700\mu Ci$

Answer 1

The correct option is B $27\mu Ci$

10 ml of diluted gas should have ${10}^4$ dis /min.
Thus 60 L of diluted gas should have ${10}^4\times \frac{1000}{10}\times 60=6\times {10}^7$ dis /min.
The activity is $\frac{6\times {10}^7}{2.22\times {10}^6}=27\mu Ci.$