Bananas Are Naturally Radioactive Due to Potassium-40

Bananas contain naturally occurring radioactive potassium-40, which makes them slightly radioactive. This isotope has a half-life of 1.25 billion years and comprises about 0.012% of all natural potassium. A typical banana contains about 358mg of potassium, of which roughly 0.04mg is potassium-40. This gives bananas a radioactivity level of about 15 becquerels (15 decays per second). Scientists actually use the 'Banana Equivalent Dose' (BED) as an informal measurement to compare radiation exposure - one BED equals the radiation exposure from eating one banana. To put this in perspective, you'd need to eat about 600 bananas to equal the radiation exposure of a single chest X-ray, or 400 million bananas to equal a fatal dose of radiation. Other naturally radioactive foods include Brazil nuts (which are even more radioactive than bananas), carrots, lima beans, and potatoes.