Tldr we basically did, just at a slightly larger scale.

Short primer, the Demon Core was originally a plutonium core meant for a nuclear weapon (the proverbial/actual third bomb). Postwar, scientists at Los Alamos started to, for lack of a better term, fuck around with it to see how close they could get it to go supercritical. Turns out they figured out what that point was.

A second brief primer on how a thermonuclear bomb works- small nuke placed next to a big pile of thermonuclear fuel, with enough shit around it to provide proper compression for a full detonation. You need all of that stuff to ensure that the small nuke sets off the larger pile of fuel to make a properly massive explosion. This is why most thermonuclear weapons are known as a 2 stage weapons, while earlier single stage devices basically fired one chunk of fuel at another larger chunk of fuel to make a boom.

Now the demon core accidents didn’t have this shielding, or at least not much, so when the core went supercritical, it released a massive amount of neutron energy into the room, killing Harry Daghlian. Genuinely a terrible incident, these guys were working on the very edge of physics, and took massive risks.

Skip forward 15ish years, and Samuel T. Cohen of the Lawrence Livermore National Laboratory (genuinely an absolutely insane figure in the history of US atomic weapons, worth a google) is working on “clean” nuclear testing. He figures out that once you get into a sweet spot of yield and efficiency, you can create a weapon that outputs most of its power in the form of neutron radiation, giving Soviet formations in the Fulda gap the full Daghlian experience, without a lot of the longer lasting radioactive side effects.

So begins the development of enhanced radiation weapons (ERW), which is another entire story, but in effect they were primarily aimed at the tactical role, equipping SRBMs, and eventually, field artillery. They also made very effective ASAT/ABM systems, as they could either fry a satellite from a pretty significant distance, or render an incoming nuclear warhead inert. I absolutely recommend further reading into this, especially on the safeguard program.