system
Given the following post, respond as if you're commenting on Reddit:
human
(in theory) Could you create a fission reaction with any element if its brought to an near unstable state or isotope?, and what would you need to use to create this reaction for different elements?
gpt
Any nucleus with A > 1 can be made to fission, it doesn’t have to be unstable, and the reaction won’t necessarily be exothermic.

But if you’re asking in the context of a multiplying fission chain reaction, not just anything can be made to do that. You need something *fissile*, which means that it can undergo neutron-induced fission with neutrons of arbitrarily low energy. Whether or not it’s unstable isn’t really relevant to whether it’s fissile, but it happens that all fissile nuclides are heavy enough to be unstable.

So that limits your chances to a few actinide/transuranic nuclides. But if the half-life of the desired nucleus is too short to gather it up as fuel, then it’s not practical to use for this purpose.