Ionization of Air byγ-Rays as a Function of Pressure and Collecting Field

The ionization of air by $\gamma$-rays was studied for pressures from 1 to 93 atmospheres and for collecting fields from 1.55 to 1009 volts per cm. Increases in ionization current of over 40 percent were observed when the potential gradient was varied over this range, thus indicating that the lack of proportionality of ionization current with pressure obtained by previous observers was principally due to lack of saturation.