Dependence of the value of m on the lifetime of ions in parallel-plate ionization chambers

Abstract

Measurements concerning the collection efficiency were made for a parallel-plate ionization chamber which has a variable space between the polarizing electrode and collector. To do so, the chamber was exposed to 60Co gamma -rays at several different exposure rates and the value of m-which is equal to ( alpha /eK+K-)1/2 where alpha is the recombination coefficient, e is the charge per ion, and K+ and K- are the mobilities of positive and negative ions, respectively-was deduced from the collection efficiencies which were determined at various applied voltages. It was found that m depends upon the lifetime of ions in the chamber (i.e. it increases from 17.1 to 18.5 MVA-1/2 m-1/2 with a decrease in the ratio of the voltage to the square of the chamber space from 600 to 20 kV m-2).