Another particulates vs radiological exposure question...

Submitted by Anonymous on Wed, 2011-03-23 17:01

Berkeley Radiological Air and Water Monitoring Forum

Thank you for posting this excellent dataset. Since I'm not a nuclear engineer, just a simple molecular biologist, can you attempt to come up with some sort of analogy for us lay people about the qualitative risk of exposure/uptake of the radioactive particles coming from Japan at different levels of your readings?

I guess I am looking for something like a BED (banana equivalent dose).

http://en.wikipedia.org/wiki/Banana_equivalent_dose

Maybe I'm just not understanding or grokking the water equivalent dose you are using.

It's clear, I think, that the current increase in "radiation" is low when compared to organic "background" sources, but most of the questions I have been getting, zoom past that part to questions like

"How likely am I to ingest a radioactive particle that may cause a cancer episode 5 10 - 20 yrs down the road?"

Thanks

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It is a psychological

Submitted by Anonymous (not verified) on Sat, 2011-03-26 16:11.

It is a psychological defense mechanism from the reptilian brain that compares debris from 40 years of mismanaged nuclear industry to bananas and sunshine. Don't let your pulse rise from this nuclear disaster, grab a beer and turn on the game!

Calculation of BED

Submitted by bandstra on Wed, 2011-03-23 22:50.

I can answer part of your question -- specifically, how to calculate the banana equivalent dose (BED), which is defined as approximately 0.01 millirem.

(By the way, the main reason that bananas and other foods -- and even your own bones -- are radioactive is because of the naturally-occurring radioactive isotope potassium-40, which we see all the time in our detectors as background. Check out any of our gamma-ray spectra -- look for the line at 1460 keV.)

If we just take the case of Iodine-131, then from from the dose calculation page, the conversion factor for equivalent dose from activity is 68.5 millirem per microCurie (uCi) for I-131 in water. The conversion from uCi to Becquerels (Bq) is 1 uCi = 37,000 Bq, so the dose conversion factor is 1.85E-3 millirem/Bq. Using 1 BED=0.01 millirem, this yields 0.185 BED/Bq for I-131.

So if we want to know the banana equivalent dose of the highest I-131 rainwater measurement of 8 Bq/L, we get 8*0.185 = 1.48 BED/L, or each liter of rainwater consumed gives the equivalent dose of 1.48 bananas. This same method can be used to convert to BED/L for other data points to put the dose in perspective.