Apr 24, 2013· Thermonuclear Weapon Designs and Later Subsections. The casing was hemispherical at one end, where the primary sphere was located . … The secondary stage consisted of the exterior pusher/tamper, a standoff gap, and a …. In a three stage weapon the radiation cases for the secondary and tertiary might be …. produced by a nuclear explosion – tantalum, cobalt, zinc, and gold.