The Determination of Saturation Currents in Free-air Ionization Chambers by Extrapolation Methods

Abstract

The usual method of determining saturation currents in free-air chambers is to plot the reciprocal of the current, j, against the reciprocal of the collecting electric field, E, and extrapolate linearly to 1/E=O. This method is valid only if the recombination taking place is initial recombination within ion clusters. Evidence is produced to show that in such chambers, at dose rates of 1 r/min or more, it is general (volume) rather than initial recombination which is taking place. Theory shows that under these circumstances one should plot 1/j against 1/E2, or more accurately against j/E2 , and extrapolate to 1/E2 or j/E2 = 0.