Banana equivalent dose

A banana contains about $450\;\text{mg}$ of potassium, of which $0{,}012\%$ is ${}^{40}$K, a naturally occurring $\beta^-$ radioactive isotope. Eating one entails an equivalent dose of $\sim 0{,}1\;\mu\text{Sv}$ (one ten-millionth of a sievert). Hence the amusing banana equivalent dose, a handy scale for communicating the size of doses to the public in intuitive terms.

The banana scale

• $100$ bananas $\approx$ a dental X-ray.
• $50\,000$ bananas $\approx$ a CT scan.
• $5$ million bananas $\approx$ the acute lethal dose.
• A day of air travel $\approx 500$ bananas.

The message is not that bananas are dangerous — they are not, at all — but that a small amount of radioactivity is inevitable and natural: it is in the food we eat, in rocks, in the air, in cosmic rays. It only makes sense to worry about a dose by comparing it with this natural background, not in absolute terms. The perception of radioactive risk, often exaggerated, should be calibrated against the numbers.

Collegamenti

Argomenti: Fisica nucleare Concetti: Decadimento radioattivo

Esercizi collegati: Esercizio svolto — decadimento del radon in cantina · Dalla legge fenomenologica all’esponenziale · Vita media di un campione misto