The irradiation system consisting of an α-source and disc holder has been developed in the Heavy Ion Laboratory, University of Warsaw. A simple exposure system for irradiation of biological samples consists of the Am-241 disc source, source holder and biological samples cultured in special Petri dishes. The irradiation system has been investigated to determine the alpha spectrum and dose distribution in irradiated single cell layer attached to the Mylar foil. Commercial Am-241 disc source of 50 mm in diameter, with a radioactive element embedded into a substrate layer was examined to established the uniformity of surface radioactivity over the disc source. The experimental device is equipped with cell dishes of 40 mm in diameter and a 6 µm thick Mylar foil bottom. Care was taken for homogenous irradiation of the cells. Dose calibration for the irradiation system was calculated taking into account source-to-target geometry.