This isn't a suggestion for a new element, but a modification to URAN. It should be added that if URAN is exposed to NEUT, then it turns to PLUT and sinks down (like how they make plutonium in real life).
In Powder Toy, the opposite occurs. Plutonum when pressurized will turn into uranium, neutrons, and stone and heat up. The uranium sinks.
i would
high five!