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WonderScience fact

Bananas are slightly radioactive. They are rich in potassium, and a tiny share of all natural potassium is the radioactive form potassium-40. In an average banana about 15 atoms decay every second, far too few to harm anyone.

Physics

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The story behind the card

Only about 0.012% of natural potassium is potassium-40, and it decays very slowly: it takes 1.25 billion years for half of any amount to break down. Because potassium is everywhere, more than 4,000 potassium-40 atoms also decay inside an adult's body every second. The 'banana equivalent dose', about 0.1 microsieverts (a unit for the effect of radiation on the body), has been used since at least 1995 to explain very small doses to the public; a chest CT scan gives about 70,000 of them. It is only a teaching aid, not a real cumulative dose: the kidneys keep the body's potassium level steady, so eating bananas does not build up radioactivity. Even so, a lorry-load of bananas can set off the radiation alarms used at US ports to detect smuggled nuclear material.

Türkçe oku
Muz az da olsa radyoaktiftir. Potasyum bakımından zengindir ve doğadaki potasyumun çok küçük bir bölümü radyoaktif potasyum-40'tır. Ortalama bir muzda her saniye yaklaşık 15 atom bozunur; bu, kimseye zarar veremeyecek kadar azdır.

Doğal potasyumun yalnızca %0,012 kadarı potasyum-40'tır ve bu izotop çok yavaş bozunur: Herhangi bir miktarının yarısının bozunması 1,25 milyar yıl sürer. Potasyum her yerde olduğu için yetişkin bir insanın vücudunda da her saniye 4.000'den fazla potasyum-40 atomu bozunur. “Muz eşdeğer dozu” denen gayriresmî ölçü, çok küçük radyasyon dozlarını halka anlatmak için en az 1995'ten beri kullanılıyor. Bir muz yaklaşık 0,1 mikrosievert sayılır (sievert, radyasyonun vücuda etkisini ölçen birimdir); göğüs tomografisinde alınan doz bunun yaklaşık 70.000 katıdır. Ama bu yalnızca bir öğretim aracıdır, vücutta birikip toplanan gerçek bir doz değildir: Böbrekler vücuttaki potasyum düzeyini sabit tuttuğu için muz yedikçe vücudun radyoaktivitesi artmaz. Yine de kamyon dolusu muz, ABD limanlarında nükleer madde kaçakçılığını yakalamak için kurulan radyasyon alarmlarını çaldırabilir.

Sources and further reading

Background reading: Banana equivalent dose
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