Measurements of Gamma-Ray Ionization Currents in Air at High Pressures and High Gradients

With weak sources of gamma-rays, ionization currents in air were measured at pressures between 20 and 200 atmospheres with collecting fields varied from less than 1 volt/cm to 4500 volts/cm. At all pressures, ionization currents were found to continue increasing with increase of collecting field intensity throughout the range employed. The ionization current measured with a particular collecting field intensity does not continue to increase with pressure but has a maximum value in the neighborhood of 140 atmospheres. Rates of collection of negative ions were found under all conditions to be greater than rates of collection of positive ions under the same conditions.