On the interpretation of current–voltage curves in ionization chambers using the exact solution of the Thomson problem

Abstract

a b s t r a c tThe I À ΔV characteristic curve of a well type ionization chamber irradiated with 192 Ir sources (0.75 Ci-120 Ci) was fitted using the exact solution of the Thomson problem. The recombination coefficient and saturation current were estimated using this new approach. The saturation current was compared with the results of the conventional method based on Boag-Wilson formula. It was verified that differences larger than 1% between both methods only occurred at activities higher than 55 Ci. We concluded that this new approach is recommended for a more accurate estimate of the saturation current when it is not possible to measure currents satisfying the condition I=I sat 4 0:95. From the calibration curve the average value of pairs of carriers created per unit volume was estimated to be equal to η ¼ 8:1 Â 10 À 3 cm À 3 s À 1 Bq À 1 and from that value it was estimated that $ 17 pairs were created on average per second for each decay of the source.