We report on the synthesis and characterization of composite semiconducting polymer - nanoparticle membranes for X-ray detection applications. The membranes are made of poly(vinyl alcohol) (PVA) organic polymer that is doped with ionic liquid (IL) to control its electrical conductivity. Tl2O3 nanoparticles with different weight concentrations are added to the polymer, and membranes are produced using solution casting method. The nanoparticles are synthesized using a microwave assisted technique under controlled temperature and pressure, and their average size is 13.0 -/+ 1.9 nm. Structural and compositional tests confirm the fabrication of homogeneous polymer-nanoparticle films. Electrical impedance tests are conducted as a function of nanoparticle concentration and temperature for the membranes, and they reveal that the dc electrical resistance of the membranes decreases with increasing both nanoparticle concentration and temperature. The activation energy was found to increase with increasing nanoparticle concentration. The membranes are utilized as conductometric X-ray sensors, and their response increases with increasing X-ray generator voltage. The fabricated composite membranes exhibit semiconducting properties, easy to fabricate, low cost, and qualify practical device utilization in the X-ray dosimetry sector.