The utilization of a position sensitive detector in tomographic systems is an attractive possibility because it is capable of furnishing the position where the ionizing event occurs. This feature can reduce significantly the image acquiring time, since a sample translation is no longer required. In this work the performance of a gaseous position sensitive detector equipping a thermal neutron tomographic system has been improved by a stepwise increase of the filling-gas (³He-enriched helium) pressure from 3 to 6 atm. Important quantitative detector parameters such as resolution, linearity and homogeneity have been measured for that pressure range, and compared with the tomographic images of test-samples. Several test-samples have been studied, all of them constituted by an aluminum cylinder containing inserts of different materials. Besides that, the modulation transfer function-MTF for the system has been experimentally obtained and compared with the expected theoretical curve. An improvement of both detector efficiency and resolution has been observed, as theoretically expected from an increase of the filling-gas pressure.
