Could you power a house with the radioactivity from bananas?

This question comes from G, who asks, "I heard bananas are radioactive. If

they're radioactive, then they radiate energy. How many bananas would you need

energy. How many bananas would you need to power a house?" Yes, bananas emit radiation, but not very much of it.

They're very safe until you use them to power a house.

Bananas are radioactive because they contain potassium, some of which is the radioactive isotope potassium 40. The

factoid about banana radioactivity was popularized by nuclear engineers trying to reassure people that small doses of radiation are normal and not necessarily dangerous. Of course, this kind of thing

dangerous. Of course, this kind of thing can backfire. Thanks to their use as a

can backfire. Thanks to their use as a radiation dose comparison, bananas now have a reputation as an especially radioactive food, but they're really not. The CRC Handbook of Radiation

not. The CRC Handbook of Radiation Measurement and Protection, the source of the original data behind the banana factoid, lists lots of other foods with more potassium 40 than bananas, including coconuts, peanuts, and sweet potatoes. A large cheese pizza might be

potatoes. A large cheese pizza might be three times more radioactive than a banana. And the potassium 40 present in

banana. And the potassium 40 present in your own body emits a lot more radiation than any of those. Potassium 40 decays slowly with the nuclei of individual atoms sitting around for millions or billions of years before quantum

randomness finally triggers their decay.

Imagine you're a potassium 40 nucleus.

Every second you flip a coin and then roll 21 dice. If the coin lands on heads and the dice all come up sixes, you decay. Otherwise, you do nothing. But

decay. Otherwise, you do nothing. But

there are gazillions of atoms of potassium 40 in a banana, which is enough that any given second 10 or 15 of them make that heads plus all sixes roll, spit out a high energy particle, and become stable calcium or argon. That

high energy particle released by the expiring potassium atom will promptly bonk into other atoms, leaving everything vibrating with a little extra heat energy. In principle, you can use

heat energy. In principle, you can use this heat energy to do work. That's how

the Mars Rover's Curiosity and Perseverance are powered. In practice,

the Mars rovers use a chunk of plutonium 238 big enough to have quadrillions of decays per second, releasing a lot of power. By comparison, the 15 decays per

power. By comparison, the 15 decays per second from our banana work out to a couple of powatts of power, roughly the power consumption of a single human cell. Even if you captured that

cell. Even if you captured that radioactive decay energy with perfect efficiency, powering a house would require about 300 quadrillion bananas, which would form a heap large enough to bury most of the skyscrapers in the New York City metro area. Radioactive decay

of potassium 40 and bananas is a terrible source of energy. But that's

okay, because you know what's a great energy source? The banana itself. A

energy source? The banana itself. A

banana contains about 100 calories of food energy. And if you incinerate whole

food energy. And if you incinerate whole bananas as fuel, it would only take about 10 bunches per day to keep your house running. Unfortunately for New

house running. Unfortunately for New York City, which we buried in bananas a moment ago while trying to make the radiation idea work. Sorry.

Radioactivity versus chemical energy isn't an eitheror thing. If you piled up a lot of bananas, they would start to release that chemical energy one way or another. The banana pile would start to

another. The banana pile would start to rot and the heat from the decomposing bananas would immediately overwhelm the heat from radioactivity. Decomposition

by anorobic bacteria deep in the pile would also produce various gases, including highly flammable methane. As

the gas bubbled up to the surface of the burning hot banana swamp, it could ignite. Gas build up from food waste is

ignite. Gas build up from food waste is a major industrial explosion hazard. So

don't worry about the radioactivity in bananas. It's the rest of the banana

bananas. It's the rest of the banana that's the real threat.