The impact of systematic effects on the areal density derived from a neutron resonance transmission analysis (NRTA) is investigated by measurements at the time-of-flight facility GELINA The experiments were carried out at a 25 in station using metallic natural Cu discs with different thicknesses. To derive the areal density from a fitting to the experimental transmission, the resonance shape analysis code REFIT was used. Large bias effects were observed using recommended resonance parameters. Therefore, neutron resonance parameters, in particular resonance energies and neutron widths, were derived from the transmission data obtained with a 0.25 mm thick Cu metallic sample. These parameters were used to study the impact of the resonance strength and sample thickness on the accuracy of the areal density derived by NRTA. (C) 2014 Elsevier B.V. All rights reserved.