Potassium-40 is the most prevalent radioactive element in the food we eat. Potassium-packed bananas are well known for their radioactivity, so much so that a banana’s worth of radioactivity is used as an informal measurement of radiation. It’s called the Banana Equivalent Dose. One BED is equal to 0.01 millirem. A typical chest x-ray is somewhere around 200 to 1000 BED. A fatal dose of radiation is about 50 million BED in one sitting.