Actually, cleanup is possible. They don't spread that much radiation. Except at maybe the centre (where people would be wiped out by the explosion anyway), radiation levels are barely lethal. It's not a neutron bomb. It would be pretty expensive and the terror effect high, but it won't turn the area into a long-term wasteland.
As for buying uranium; is it enriched and ready for practical fission? I'm not saying it's illegal, I'm saying you'd probably be monitored. You could make a dirty bomb out of basically any radioactive material though, and there's plenty of that out there.
As for buying uranium; is it enriched and ready for practical fission? I'm not saying it's illegal, I'm saying you'd probably be monitored. You could make a dirty bomb out of basically any radioactive material though, and there's plenty of that out there.