Did you know bananas are slightly radioactive? Bananas contain high levels of potassium. Radioactive K-40 has an isotopic abundance of 0.01% and a half-life of 1.25 billion years. The average banana contains around 450 mg of potassium and will experience about 14 decays each second. It's not something you need to worry about, since 0.01% of the potassium already in your body is K-40, plus the element is essential for proper nutrition. If you have a banana for your lunch you aren't going to set off a Geiger counter. If you carry a produce truck full of them, then you might have a noticeable radiation signature. The same is true if you are carrying a lot of potatoes or potassium fertilizer.