Secondary radiation shield for 81Krm gas generators

Describes a secondary shield to reduce the radiation dose of 81mKr generators to approximately background levels. The shield consists of a Pb cylinder (internal diameter 150 mm, outer diameter 230 mm) built up from interlocking Pb rings. The body of the cylinder is encased in a 6 mm thick nylon sleeve. The base ring is bolted to a circular mild steel base plate (356 mm diameter).