A rigorous method to determine the saturation current of ionisation chambers in the recombination regime

Abstract

In this work we apply a rigorous method to obtain the saturation current Isat of a 4πγ ionisation chamber under very intense γ radiation from a 192 Ir solid source ranging from 27 GBq (0.75 Ci) to 4.1 TBq (110 Ci). We determine Isat by fitting experimental results to a finite series of powers of 1/V 2 obtained from the perturbative solution of the Thomson problem when space charges are neglected. We show that only few terms of the series expansion are needed to achieve a good fit. We conclude suggesting that this method should be preferred to traditional ones when inferring Isat from measurements in the recombination region in the case where volume recombination is predominant.