Bananas always get the hype for being particularly rich in potassium-40, which is the unstable isotope, but Brazil nuts have far more, and potato and carrot are about as radioactive as banana.

The problem is it also contains a non-insignificant quantity of banana.

Don’t they annihilate each other when they encounter matter? How can a banana contain antimatter safely?

That's a good idea for Star Trek. They allready had the mushroom powered warpdrive. So a starship powered by bananas isn't that far fetched.