Saturation Characteristics of a Spherical Ionization Chamber and a Determination of Boag's Constant for Air

Abstract

Thomson and Rutherford's¹ initial investigations of the saturation characteristics of a parallel plate ionization chamber were followed by theoretical treatments by Thomson², Mie³, Seeliger⁴ and others. More recently, Boag and Wilson⁵ have shown by dimensional analysis that the collection efficiency, f (that is, the ratio of the measured current, i, to the ideal saturation current, i_s), is a function of d²q^½V⁻¹ where d is the distance between the plates, q is the rate of ionization and V is the applied voltage. Through the introduction of certain assumptions, they derived the following equation for the generalized saturation characteristic: k₁ and K₂ are the mobilities of the positive and negative ions respectively (that is, it is assumed that the current carried by electrons is negligible); α is the recombination coefficient; e is the charge per ion; m is Boag's constant.