[en] Gas filled proportional counter employed for neutron spectrometry may introduce distortion on the resulting spectrum due to the so called wall effect. This can be studied with passive detectors such as P ADC and to estimate the spectrum uncertainty. Results giving information on the charge particle rate entering the proportional counter active detection zone provide the extent of the perturbing effect due to different cathode wall material. In this study we point out some case material (Pt, Al, Ni) response to a radioisotope produced neutron field employing passive detectors. Comments on the resulting data and suggestions on possible materials to build a low wall effect proportional counter for neutron spectrometry are given. (Author)