It is widespread. All you need is 2 sub critical masses of fissionable material, an artillery tube, and some explosive. It won’t be pretty, but it will work.
Iran will have an atomic device inside of 2 years. Hell, the Norks and the Pakis developed them. Iran is technologically superior to both of them put together.
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I said that the basic physics of this is well known. It was well known in the 1940's. That isn't even one of the many the significant issues with creating a nuclear bomb.
The Norks and Paki's did not develop them. Again, go back and read the original post. Only ONE country has actually ever developed a nuclear weapon, and that is the United States. All of the others had help [Britain, France, Israel, India, China, Pakistan], spies [Russia, China] or violated the NNPT in order to get the technology [South Africa, North Korea, Iran and all of the others except Britain and Russia] or some combination of the above.
I taught nuclear physics for years to Nuclear Engineers, Technicians, and Physicists at Senior level to undergraduates. None of my students would have had the slightest idea how to build a nuclear bomb without further, graduate level and highly technical instruction. People who say this is easy to do DO NOT KNOW WHAT THEY'RE TALKING ABOUT.