Fire detectors utilizing an ionization chamber not subject to condensation of water vapor during variations of temperature

An improvement to fire detectors of the type comprising an ionization chamber having a radioisotope source with an emitting surface turned towards the inside of the chamber and which creates in the atmosphere of the chamber linked with the atmosphere to be monitored a substantially constant ionization, the said source being permanently maintained at a temperature above that in the chamber by the Joule effect using an electrical resistor in such a way as to prevent the condensation of water vapor on the source during the sudden temperature variations in a very humid atmosphere, wherein the electrical resistor is embedded in a ceramic support, said support being attached to the rear non-emitting surface of the source.