Influence of ambient humidity on the current delivered by air-vented ionization chambers revisited

The influence of ambient humidity on the current delivered by a vented ionization chamber has been re-investigated. A Nucletron 077.091 well-type chamber together with a (192)Ir HDR brachytherapy source was enclosed in a climatic test chamber and the current was recorded for various humidity values. Great care has been taken for the design of the experimental setup in order to obtain reliable measurements of currents and humidity values inside the chamber active volume. A +/-0.35% linear variation of the measured currents has been observed over a common range of humidities. This result is larger than the expected variation. No formal explanation of such a discrepancy has been found yet, however the present results could lead to a set of recommendations.