English: Radiation source for the atmospheric detection chamber of a Pyrotronics F3/5A is an alpha source (Am-241 in laminate foil) of annular configuration. The source is mounted about the upper end of a support rod assembly as shown. For calibration purposes, a radiation absorber in the form of a flanged cap (AKA 'shroud,' 'bonnet') is mounted to the upper end of the support rod. The cap is movable axially of the rod, and during calibration of the detector it is moved to a position where its flange intercepts and absorbs a selected fraction of the radiation which otherwise would penetrate the ionization region of the atmospheric chamber. Technical commentary: Americium-241 source foil (gold-coloured item) soldered to a support rod with user selectable exposure via screw-mounted shroud. Rod assembly is part of a Pyrotronics® model F3/5A ionization technology smoke detector manufactured in 1971. Original activity of all source foils in the unit was 80 µCi of Am-241. The rod mounted source foil contained approximately 60 µCi Am-241 of the 80 µCi total. Shroud has been fully raised to show how source foil is mounted. Safing and conditioning of this model involves removing support rod assembly, applying heat from a soldering pencil to the center of the rod (but not touching the foil or solder), and then allowing the ring to detach when solder has melted. Foils are kept with others until final disposition either by dissolution and reprocessing of the solution for recovery of the elements or by immobilization via vitrification and finally burial as radioactive waste.