3/28/2010 (midnight SMT) — So, by all meteorological forecast models, the “radioactive cloud” should now be spreading its menace to the Western US, and soon most of the Northern Hemisphere. If you haven’t seen the models yet, see a previous post, ‘Radiation Cloud Movement’, which gives easy access to those models. But those are models, I want facts. Best place still is the link I listed on my USA page for UC Berkeley: http://www.nuc.berkeley.edu/UCBAirSampling.
UC Berkeley has announced that West Coast rain has traces of radioactive iodine (I131,I132), radioactive cesium (Cs134, Cs137), and radioactive tellurium (Te132) according to their Nuclear Engineering Air Monitoring Station. Yesterday they logged:
“3/26 (6:20pm): Rain water sample results posted for 3/24 – 3/25. I-131 and Te-132 activities are lower than previously observed (3.12 and 0.27 Bq/L resp.) while Cs137 remains near the high point at ~0.5 Bq/L.”
I-131 @ 3.12 Bq/liter for rainwater on the West Coast. That’s perhaps not very harmful, but definitely significant. (“safe levels” for infants supposedly are 100 Bq/liter, at least that’s the Japanese standard). Bq is ‘Becquerel’, a unit for radioactivity expressing “disintegrations per second”. Iodine-131 has a half-life of 8 days and is genrally considered dangerous for about 3 months.
Cs137 @ 0.5 Bq/L for rainwater on the West Coast is well below levels seen in Japan, but… a bit troubling nonetheless. The half-life of Cesium-137 is 30 years, leaving it dangerous for about 600 years. The radiation dose from drinking such water may still be very low (lower than radiation exposure on a regurlar plane flight from coast to coast in the US), but… on such flights you don’t get served drinks with radioactive Cesium, which if you were to drink it could end up in tissues and do unpredictable harm. So the comparison to X-rays, flights, etc, is only half the gauging.
Using the Rad Pro Calculator, if I were to drink 1 liter of this Cesium-137 contaminated California rainwater, what would be the equivalent dose? Again, it depends on the distance. Reported reading are often “just over the surface”, so let’s put in Cs137, 0.5 Bq and choose different distances to get an idea of the equivalent dose:
1cm —-> ………………………………………… 0.0003820 µSv/h
(1 inch = 2.54 cm / 1 cm = 0.394″ )
0.1cm (a millimeter) —-> ………………. 0.0382047 µSv/h
0.01 (like the ticknes of hair) —-> …. 3.8204886 µSv/h
0.001 (“direct contact”) —-> …… 382.0490020272 µSv/h
So if I’m in the rain, the level of extra radiation is truly “insignificant”, and even swimming in it would be “on par with eating a banana”, so to speak, but if I were to drink it, the radiation exposure would be very limited to the very cells the Cs-137 were to come in contact with, and probably only for a fraction of a second, so the kind of µSv/hr numbers that would make a comparison possible with airline flight, X-rays, etc., is likely to make this rainwater look totally safe. Looks like nothing to be alarmed about, yet… I’d feel a little apprehensive of drinking it, to be honest. The real danger, if one were to manifest in North America, is from accumulation in food crops and plants eaten by cattle. It will be interesting to see what UC Berkeley’s results are for that. Check there FAQ page for some basics: http://www.nuc.berkeley.edu/node/2044#others