Bananas are naturally radioactive, though not in a way that is dangerous to humans. They are rich in potassium, an essential mineral for heart and nerve function. A very small fraction of all potassium is the isotope Potassium-40, which is radioactive. Because of this, a truckload of bananas can occasionally trigger radiation sensors at ports or border crossings. To put the danger in perspective, the 'Banana Equivalent Dose' is a real (though informal) measurement used by nuclear scientists. You would need to eat about 10 million bananas in a single sitting to die of radiation poisoning—though the 400 tons of fruit would likely kill you long before the radiation did. This fact serves as an everyday reminder that radioactivity is a natural part of our environment.