The Effect of Humidity on Ionization Measurements with Cavity and Free-Air Chambers

Abstract

Various authors (1, 2) have indicated the magnitude of the correction required to convert ionization measurements in moist air to a standard condition of dry air. This correction for cavity chamber measurements depends on relative values of stopping power, density, and average energy to produce an ion pair for water vapor and dry air. In the derivation of this correction, the water vapor and dry air are assumed to respond independently to the radiation. To test the validity of the correction, it was decided to measure the ionization produced in cavity chambers under widely different humidity conditions, but with all other conditions unchanged. The chambers used are spherical and have an air volume of about 1 cc. The walls are of sufficient thickness to achieve electronic equilibrium. The results of the cavity chamber measurements are given in Table I. All these measurements show that the effect of humidity upon the chamber current is very much smaller than predicted. Since the densities of water vapor and...