Variations in response to radiation of a nylon-walled ionization chamber induced by humidity changes.

The volume of nylon-walled ionization chambers varies with relative air humidity due to the hygroscopic properties of nylon. A 6% increase in exposure calibration factor of a commonly employed 0.6 cm3 nylon-walled ionization chamber was observed when the relative air humidity decreased from 98% to 11%. The increase as well as the decrease in volume shows an initial fast change during the first day followed by an exponential change with half-lives of about 1.2 days and 2.4 days, for water uptake and water loss, respectively.