Measurement
A rem (roentgen equivalent man) is a unit of equivalent dose, effective dose, and committed dose, which are dose measures used to estimate potential health effects of low levels of ionizing radiation on the human body.
A rem is a large dose of radiation, so the millirem (mrem), which is one thousandth of a rem, is often used for the dosage commonly encountered, such as the amount of radiation received from medical X-rays and background sources.
The average person experiences a dose of about 620 mrems per year. International Standards consider exposure to as much as 5,000 mrems (5 rem) a year safe for those who work with and around radioactive material.
Simply examining the average kitchen, one finds a cornucopia of items that emit enough radiation to detect with a Geiger counter in both man-made consumer products and natural foods. Avocados, bananas, bricks and smoke detectors all give off gamma radiation but at levels which are incredibly low. Brazil nuts are the most radioactive items we eat. Potassium-40 packed bananas are well known for their radioactivity, so much so that a banana’s worth of activity is used as an informal measurement of radiation, called the Banana Equivalent Dose. One BED is equal to 0.01 millirem.
Did you know your coffee is radioactive too? Carrots, white potatoes, red meat, and lima beans all contain roughly the same amount of potassium per kilogram, and thus radiation as bananas.
However, in spite of all this, you actually have little to worry about the radioactivity in your food. Even at the often-obscene levels that Americans drink coffee, there’s no danger whatsoever. And for reference, you’d have to consume between one and two million kilograms of Brazil nuts to reach a potentially lethal dose of radiation. (2)