[en] Radioactive iodine is a typical fission product in nuclear power reactors. Of the many iodine isotopes that can be generated in nuclear reactors only four are considered as radiobiological significant. These are: ¹²⁵1 (T_1/2=60 days), '1³¹I (T_1/2=8d), ¹³³I (T_1/2=21h) and ^I35I (T_1/27h). The chemical forms that have been identified in heavy water reactors are I₂ (elemental), organic iodides (CH₃I), Inorganic iodides (HOI, HI) and LiI. Radioiodine is, generally, released as a gas but can be adsorbed on air particulates to form radioiodine contained aerosols. Therefore. its monitoring has to include both gas and aerosol sampling. A new monitoring system, RIS (Radioactive iodine Sampler), has been developed at the NRCN to monitor radioactive iodine (gas and aerosol) on-line in workplaces. This system samples radioiodine at a 60 L/min rate through a transport line connected to a filter holder. The filter consists of a cartridge containing activated charcoal with TEDA for iodine gas adsorption with a membrane for aerosols' retention in from of it. The radioiodine filter cartridge (F and J product code: TE2C) has a diameter of 2 1/4 inch and height of 1 inch . The gas adsorbent is coconut shell carbon type activated charcoal with 5% (by weight) TEDA impregnation and has 30x50 mesh size. This paper presents the aerosols' sampling characteristics of the RIS system including their transport in the sampling line and filter holder. The adsorption of iodine gas on the transport system components is negligible