Hacker News Reader

Comment by adsfqwop | Hacker News Reader

Btw. just for curiosity, there is a difference in the source of radiation as it pertains to how dangerous it is.

Banana (potassium) radiation is mostly harmless to humans. Nuclear weapon or reactor radiation (for example caesium) is not.

The Banana equivalent dose is therefore a bit of a misleading term, and I have sometimes seen it used to dismiss other more harmful radiation sources as harmless, because of this incorrect banana comparison.

http://www.washingtonsblog.com/2013/04/fake-science-alert-fu...

Here is an example of using the banana comparison in an incorrect manner:

http://www.forbes.com/sites/timworstall/2013/08/10/the-fukus...

View on HN

To clarify, the gamma energy from K-40 in bananas is around 1.5 MeV, which is dangerous to humans. It's not the most dangerous, but it is dangerous in significant amounts (which are much much higher than what is in a banana).

A BED is usually taken as 1 micro-Sievert. Sieverts are a unit for measuring the biological effect of radiation, hence they are normalized to adjust for how harmful the given type of radiation is. A dose of 1 Sievert represents a 5.5% chance of eventually developing cancer. 1 Sievert is 10000000 BEDs.

The part that is a bit misleading about the BED is that it's not the same as the dose you get from eating a banana. This is because of how potassium is absorbed in the body; all the K-40 in the banana isn't staying around in your body. The BED is the dose you would be exposed to for absorbing the equivalent amount of K-40 in the same number of bananas. Bananas are fine for putting small doses or activities into perspective since the biological effects are negligible, but are not really great for comparing against more significant doses.

It isn't so much the source of the radiation, as it is what your body does with the material. When you eat a banana, your body gains additional potassium, and over the next several days your kidneys will expel that excess. So, your exposure to the tiny amount of Potassium-40 in the banana is very brief. OTOH, your body treats the Strontium-90 in nuclear fallout like calcium, depositing it in your bones and bone marrow subjecting you to continuous radiation exposure. Likewise Iodine-131 will concentrate in the thyroid.

What about then if you eat a banana daily, so there is no chance of fully expelling the potassium

Bear in mind that your body always contains potassium (mostly non-radioactive, but a tiny bit is radioactive). Eating a banana just slightly increases your exposure for a short time.

If we take a look at our handy dandy xkcd radiation chart[1], we can see that eating a banana every day for a year exposes you to about 36.5 uSv radiation, slightly less than you get during a six hour airline flight. By comparison, the potassium naturally contained in your body already exposes you to 390 uSv radiation in a year.

[1]: http://xkcd.com/radiation/

Reply on news.ycombinator.com