There was once an article in a pop sci magazine 25 odd years ago about how to build a nuke in a house; basically a pipe / barrel from the attic to the basement, a concave bit of plutonium or the right kind of uranium in the basement encased in a good carrier like concrete, and a convex matching part at the top of the barrel. Explosives behind the top one, launch the one towards the other, ????, nuke. In theory.
That said, if it was that easy, I'm sure we would've had terrorist attacks with nukes already. Or if terrorism was that big an issue. I don't know if it hasn't happened yet because technology and three-lettered agencies are doing their job right though.
Casting, machining or welding plutonium into the right shapes and purities without killing your self, or some of the other exotic metals, without killing your self or making your neighbours sick in a sub 1-3 week horizon is incredibly challenging. The exact geometries you need to achieve aren’t easily available either neither is measuring is you achieved them without again killing your self.
Getting a dirty fizzle is a lot easier which is why people are afraid of dirty weapons by terrorists.
Getting the right type of plutonium in sufficient quantity is an order of magnitude harder than either of them - there is essentially no naturally occurring plutonium, it only comes as a side effect of neutron bombardment of specific isotopes of Uranium, which are already hard to seperate, and only under specific conditions are the right types of plutonium isotopes to be useful produced. And even then, it’s non trivial to seperate them.
The whole thing is a giant, high profile, and dirty mess.
Making the entire thing efficient enough to actually be delivered to a target is also another matter. This requires precise calculation of the geometries and very precise grades of plutonium, barrel pipe, and explosives. How do you even keep the gun type shapes from deforming in the barrel?
[Cut to me in 1999 driving my old station wagon down to the local hardware store to pick up a few kilos of highly purified enriched uranium and some C4]
>> ,I'm sure we would've had terrorist attacks with nukes already. Or if terrorism was that big an issue
There are two problems with that statement. Let’s examine them
Firstly, does majority of terrorists want to nuke NewYork? If you gave 9/11 bombers a 5 megaton warhead, would they use it? You have to remember that many of them imagine they have a just cause.
Second, imagine you are could make a nuke at home and were completely immoral, who would you sell it to?
There are many evil governments and organisations that could pay more and be better clients than terrorists.
That said, if it was that easy, I'm sure we would've had terrorist attacks with nukes already. Or if terrorism was that big an issue. I don't know if it hasn't happened yet because technology and three-lettered agencies are doing their job right though.