RDX is a component in C4, invented prior to WWII. The Russian equivalent, and an exact equivalent, is Semtex.
The explosive used to implode nuclear devices is Pentolite, or a more recent substance. It is probably and RDX-based material, maybe PETN. What sets it aside from its cousins is its ability to be precisely molded without expansion or contraction. When cool, it maintains its shape even through fairly wide temperature excursions.
I suspect the Russians took electronics hardening into account when they made those nukes. Besides, a-bomb cores aren't particularly radioactive until they are compacted into a critical mass.
We arn't talking home-made weapons.