A sample of ${ }^{14}{\mathrm{CO}}_2$ was to be mixed with ordinary ${\mathrm{CO}}_2$ for a biological tracer experiment. In order that $10{\mathrm{cm}}^3$ of diluted gas should have ${10}^4$ dis/min, what activity (in $\mu \mathrm{Ci})$) of radio active carbon is needed to prepare 60 L of diluted gas at 1 atm and 273 K?

$\left[1\mathrm{Ci}=3.7\times {10}^{10}\mathrm{dps}\right]$