Reactions to the atomic bomb.
How would Aliens (especially sane Havenworlders) react to the information, that Humans use nuclear fisson.
"You did WHAT with URANIUM!!!"
"And this ..... is the FIRST THING your species came Up with after figuring IT Out ?!?"
"You have HOW MANY of Rhode Doomsday devices????!!!!!!!!!"
Imagine how a scared class 6 deathworlder would react ^^
Class 6 is theoretical only (so far) but yeah, they MIGHT be immune to radioactivity in natural amounts. The idea of making MORE radioactivity to shit on your enemies might even be too extreme for them.