you asked: "The first stage is a fission explosion in which a high explosive (usually something like TNT or RDX bound into a polymer matrix) compresses a core (the "primary") of plutonium or enriched uranium to create a supercritical mass. Fusion fuels (deuterium and tritium/lithium-6) may be added to the primary, which help to keep its core supercritical longer; this is called a "boosted fission" or (confusingly) "boosted fusion" device." you need a pliable explosive: RDX is easy to obtain as its an industrial compound made to be molded. the hard part is getting about 35 pounds of plutonium and not dying in the process. plutonium is dense like lead so 35 pounds is about the size of a regulation baseball. i would look at making deuterium for enrichment because you can extract it slowly from sea water with a car battery, and because handling lithium with tritium is annoying (tritium decays quickly into water vapor which the lithium likes too much). you will need something you can synchronize to cause all the the RDX sections to react (ie "explode") simultaneously. back in the 1980s we would have used professional photographic flashbulb controllers, but today i would bend some integrated circuits harvested from fisher-price toys since toys-r-us are everywhere, to drive 64 U-bin luxeon LEDs. The LEDs cost about $5.00 each so that might be pricey. all this info is and has been freely available from Wikipedia for more than a decade.