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Source control system for the generation of homogeneous 220radon reference atmospheres


For the generation of a reference atmosphere, ten 228Th sources are installed in the thoron progenies chamber. These sources from which 220Rn emanates are electrolytically precipitated on metal foils. They are 20 mm in diameter. Each single source is inserted into a lead cube (10x10x10) cm3 in thickness) by means of a drawer. Opening and closing of the drawers with the sources inside is controlled from the outside via the source control system. If a source is immersed in the lead cube, this serves to shield the ionizing radiation and to reduce 220Rn and its progenies.


Figure : Sketch (on the left) and photo (on the right) of the source shielding. From these modules,
ten individually controllable systems are located in the thoron progenies chamber.

The ten lead cubes are uniformly distributed in the chamber on a support system. All sources can be drawn out simultaneously or separately. The drawer is inserted and drawn out via a thread rod with driving rods. Positioning of the drawer is determined via two limit switches.

The source control system was manufactured in a cooperation of the Working Groups "Detector Development", "Unit of Activity" and "Environmental Radioactivity" of Division 6.