I've known some navy engine guys. They sleep next to the nuke. Oh sure theres shielding, but nukes are transmuting matter and energy and often as pure energy "appears", it is in an "exotic form" that lasts but an instant - just long enough to go through a guy sleeping next to the nuke, before it changes into something more normal. Anyway those guys are a bit more toasted than the average "bubble head". No I imagine he wasn't allowed near any material, but he may have guarded it.
Its hard to imagine that he did what he did and survived very long. However imagine if he had the intent of creating a "fission device" and instead of making a small beam of neutrons, he had put the material in the middle of a cleverly layered "onion", he could have a much larger "hotter" operation than he did, by maybe a hundred or thousand fold. His intent was to make a breader reactor, and he did - he had uranium absorbing slow neutrons and radiating light and other things and transmuting into other isotopes and elements, perhaps some plutonium and he was about to cross a line with refined radiun when caught, but the point is that he had home enriched fissionable material. It sounds pretty easy to me, however I am skipping all details so the homeland security guys don't come speak at me. The critical point (ha ha pun intended) is that a simple home made breader reactor could work at all. Obtaining raw materials and changing their form into weapons grade material is a daunting process, but then there is a tremendous amount of engineering involved in making a nuke of any kind from that material, but and this is a very big butt we can only wonder what the super computers simulating nuke designs have to say about how the laws of physics change near the "edges" like at 10 million atmospheres of pressure and a billion degrees. Perhaps a pin head sized material or even smaller, perhaps very small bits of material could "fuse" under enough pressure. I mean if you get one electron and one proton to collapse into a netron and a neutrino and a burst of energy, then you are transmuting matter into energy, and one gram of matter transmuted into energy could put the empire state building in orbit.
Jim