Detecting K-40 in bananas with Radiocode RC103

You may get some better results using some heavy shielding to reduce the natural K-40 background. Another way would be to use dried (dehydrated) banana pieces as they should contain more K-40 per gram of bananas and the reduced water content should allow the radiation to be emitted more easily, as the water molecules will show down the emission slightly. Crush the dried banana pieces into tiny pieces then surround the whole sensor of the radiacode in the dried banana. Or maybe do both and that may show something better. I would also let it run for longer, maybe 7 days or so.

Hmm, that's interesting. I had always thought the fleshy part was more active, and ChatGPT has just confirmed that for me -

In terms of potassium-40 (K-40) radioactivity, the inside of the banana (the edible part) is more radioactive than the skin.Here’s why:

• K-40 makes up a tiny fraction (~0.012%) of natural potassium.
• The majority of potassium in a banana is found in the fleshy part, because that’s where nutrients like potassium are stored to support the plant’s growth and fruit development.
• The peel has far less potassium than the inner fruit—so it contains less K-40 and is thus less radioactive.

With regards to shielding, thin copper ((or aluminium foil) on the inside) is to stop x-rays being emitted from the lead shielding when gamma rays hit it. About 1-2cm of lead should be good. If you make from it bricks, make sure you have two layers and overlap any inner joins between bricks. An optional outer layer could be made from steel, concrete or thick plastic to reduce stray gamma and neutrons.

I think this is the video you are referring to:



I fed the transcript and a brief into ChatGPT, and it agrees with the video, and that the skins, once turned to ash, will contain more K-40, which kinda contradicts what it originally said, but seems the carbonizing/reducing (concentrating) to ash makes a difference. I remember some time back when I was first learned about K-40 in bananas that I read somewhere that as the banana ripens a lot of the minerals migrate towards the skin, and according to ChatGPT that is actually the case. So it may be the older and riper the banana is, the more K-40 is in the skin as opposed to the fleshy part.

It seems there is quite a bit more to this - as the banana ripens, the minerals migrate towards the skin, and concentrating the skins (burning to ash) makes the readings. Adding the water to the flesh and not the skins (maybe he did add to the skins, but I didn't see that) could have caused some minerals to leave the sample via the water evaporation. 

I would say his experiment is just one way the experiment could be conducted. Slightly inconclusive, and requires more experimentation. I.e. repeat process and see if the results are the same. Try with well ripened bananas, and then with super fresh, still green, unripened bananas. Also dehydrating the bananas, both flesh and skin, instead of concentrating down with heat may offer different results.

Something else to bear in mind is, bananas from one tree may contain more or less potassium than another. Extra potassium may have been added during farming, as potassium is used as a fertilizer, or different soil may contains more or less potassium, which the tree would take up from the ground and move to the fruit.

It's become quite an interesting topic, much more than just 'bananas are radioactive.'

I have attached the full ChatGPT conversation as a PDF to this post.