Cylindrical diffusion chamber for radon measurement equipped with nuclear track detector (LR115) and electret, was considered in this work. Electrets were used to attract positively charged radon progeny created by radon decay inside a chamber. Sensitivity of such setup has been determined for different distances between electret and LR115 detector. A possibility of progeny separation was observed, due to the existence of upper energy detection limit of LR115. Different geometries of detector and electret were tested in order to optimize this kind of device.