Lolzy about that less powerful reaction than plutonium... it should be same power.

Francium isn't gas it is solid.

Ok lolzy little less power cause even then it will be more powerful used propertly.

As far as new radioactive elements, I think the only thing that you could even argue as a "need" is a solid radioactive element - something like Radium. For every particle of RAD that decays, 2-4 neutrons can be emitted; decayed RAD can become METL or BMET or whatever. Also, this should not be an escalating reaction; decay should be constant.

Yeah, something like that.