let's not forget that nation-state(s) (maybe singular, but not certain) have weaponized Polonium[1], and also the ubiquity of americium-241[2] which could be used similarly...Outside the human body but readily available for inimical ends...

[1] https://en.wikipedia.org/wiki/Alexander_Litvinenko [2] https://en.wikipedia.org/wiki/Smoke_detector