That's right, the cluster of bananas sitting in your local grocery store has the ability to set off a Geiger counter. Bananas, among many other foods, have a natural half-life resulting from the high levels of potassium. So relax, just because they are radioactive doesn't mean they are deadly or can cause you to mutate. However, knowing that bananas are naturally radioactive didn't stop Japanese authorities from banning them after the tsunami in 2011, which caused the Fukushima nuclear disaster. Even if they had been more supportive of the banana, the terrified people weren't willing to take any chances on food that was even remotely radioactive; let alone, food that came that way naturally.