Some unexpected behaviours of PTW/Nucletron well-type ionization chambers.

Some unexpected behaviours of PTW/Nucletron well-type ionization chambers have been discovered. A significant undesired detection volume is present in the region surrounding the electrical terminals. A finite-element code has been used to compute electrical fields in this region, and it showed that the magnitude of the undesired volume was dependent on the electrical connector type. An experimental confirmation of this assumption has been obtained. A source activity dependence of the calibration coefficients has also been revealed. A set of recommendations for the optimal use of this detector is proposed.