The present invention relates to an ionization device of cylindrical shape comprising a removable ionization chamber (30) that can be inserted into a base (39), this chamber having an anode (31) formed from a central bar made of electrically conducting material and a cathode (34) made of electrically conducting material surrounding said anode, the anode and cathode both being connected to two cylindrical flanges (32, 33) which are centred on the anode (35) and placed perpendicular to the latter at its two ends, the cathode (34) being formed from wires connected to the peripheral part of these two flanges (32, 33), in which each of the two flanges (32, 33) incorporates a circuit for collecting parasitic currents and is isolated from the anode (31), in which the two flanges (32, 33) are connected together by a bundle of wires connected together via conducting tracks internal to these two flanges in order to form the cathode (34), and in which a final wire, parallel to the others, connects the parasitic current collection circuits internal to these two flanges.