Bananas do contain radiation and can poison and kill someone but you would be unable to consume enough bananas to be killed or harmed by the radiation that bananas contain.
To be poisoned and killed from radiation from bananas you'd have to consume 10,000,000 bananas at once which is impossible.
Also to even get any symptoms of radiation poisoning from bananas you'd have to consume 274 bananas everyday for seven years.
That would be really hard to consume 274 bananas everyday for 7 years straight because although I love bananas I would get sick to my stomach just trying to eat that many bananas and would get tired of them too.
So you can eat as many bananas as you want too and you'd still be safe from radiation poisoning since it's impossible to eat enough bananas to cause a problem.
Bananas are very healthy for you too so you'd be benefiting by having better health when eating bananas.