I would make it so it can serve as a kind of fallout after a nuke blows up.
That way, you can more accurately portray why nuclear weaponry is utterly terrifying.
It would also, as a plus, still have the fact that it is still the only element to spontantaneously emit neutrons.
You make a valid point though.
Maybe set the limit to 100 and tie the chance for emitting a neutron to how much tmp it has left.
the formula would be like y=((100-tmp)/50)*basechance , meaning before it reaches 50, it actually has increased ability to emit
neutrons, whereas after passing that point, it slows down.
Due to that behaviour, it also shows radioactive decay "realistically"
Its just a suggestion though.
I am not a dev and I would never claim to know close to what a dev knows, so its my two cents.