Why I-131 and Cs-137 counts are so different in rain water?

Submitted by Anonymous on Fri, 2011-03-25 14:05

Hi,

Thank you for putting up such a tremendous public service effort.

I have a question about the relatively large difference of the I-131 and Cs-137 counts. An Australian group estimated that the Fukushima plant has already released 20% as much I-131 and 60% as much Cs-137 as the Chernobyl incident. So why are there much less Cs-137 counts in the rain? Is it because:

a) Less Cs-137 is generated in the reactor than I-131 to begin with,

b) Cs-137 cannot travel over air as well as I-131, (if so, why)

c) Detection efficiency is lower for Cs-137 than I-131.

Thank you! I am looking forward to the tap water test, too. If you need tap water samples from more regions, I can bring over some tap water from Novato. Thanks!

Joe

‹ Reactor three is cooling but is fuel in reactor ?tepco to check Fukushima Unit 3: Steam-Explosion Theory ›

Fukushima

Submitted by Anonymous (not verified) on Mon, 2011-09-05 15:10.

Could cesium 137 be present in house paint that was manufactured during Fukushima? If so, could it remain coated on walls and be detectible at small amounts by a Geiger counter? Thank you for your time.

The actual reasons are

Submitted by dchivers on Sat, 2011-03-26 11:43.

The actual reasons are somewhat unknown but we know a couple of things:

Cs137 has around twice the cumulative fission product yield than I131 but,
The vapor pressure puts iodine at 260k (8 deg F) at 1atm and cesium at 418k (292 deg F) at 1atm.

This means that iodine is released at room temperature (and lower) and cesium release requires much greater temperature. In general, this relates to the rates of release so iodine will always release at a much greater rate than cesium.

b) is unknown at this point, but we will be looking into this.

c) We have calibrated our detector and the detection efficiency is taken into account.

We just took samples from Strawberry creek to try to get an idea of the runoff pathway quantification and we will be starting to look at tap water next week. Currently we have two setups running 24-7, so if it stops raining, we can move on to other more interesting liquid tests (tap water, milk, etc).

Thanks, Dr. Chivers. After

Submitted by Joe (not verified) on Sun, 2011-03-27 23:32.

Thanks, Dr. Chivers.

After reading your reply, I have one more question: If the vapor pressure for iodine is so low, then when you concentrate the 5 liter rain water in the oven to get it down to 1 liter by baking (as you stated in your methodology section), wouldn't most iodine 131 have escaped?

Would it be possible that you have confused iodine gas with iodide? I think I-131 from the reactors exists in the chemical form of iodide, not iodine gas, and the vapor pressure that you cited is probably for the gas.

Thank you for your reply!
Joe

Ahh, very good question.

Submitted by dchivers on Mon, 2011-03-28 10:46.

Ahh, very good question. And we did ask this question of our own data soon after we started posting results. We did a test with a 1L non-reduced and a 5L to 1L reduced on the same sample water and counted both. To within our current error, we did not see a difference in the I-131 counts (corrected for volume and decay time). This proves that what we are collecting is not I-131 atomic, but I-131 incorporated in particulate matter, which would not necessarily be volatile during the reduction process. The exact chemistry of iodine in the atmosphere is unknown at this point and there will be a lot of work to be done to understand this part of the data. In Fukushima, the I-131 would be closer to atomic form and therefore would be released at a much lower temperature. But, there is a lot of uncertainty in the form of the iodine when released because it is dependent on where in the system the release actually occurred.

Hope that makes sense.

Strawberry Creek... Tritium?

Submitted by Anonymous (not verified) on Sat, 2011-03-26 13:09.

I recall in the late 1990s there was some stir in the local alternative press about tritium contamination in the area in and around Strawberry Creek that purportedly came from Lawrence Berkeley Labs. It'll be interesting to see if there is any tritium detected.

From the reading I've done

Submitted by Anonymous (not verified) on Sun, 2011-03-27 19:16.

From the reading I've done on this subject, it seems to be an overreaction on the part of some "alternative press."
By this time much of it has diffused away, and about half has decayed since the labeling facility producing the tritium shut down.

Unfortunately for us this is a moot point anyway, since tritium will not be detectable in our system. It only emits a low-energy beta particle, which is too weak to see in the germanium detectors we are using.

Tritium is not produced in

Submitted by Brian (not verified) on Sat, 2011-03-26 16:42.

Tritium is not produced in nuclear fission reactors such as those at Fukushima.

Tritium is produced in

Submitted by Anonymous (not verified) on Mon, 2011-03-28 01:01.

Tritium is produced in nuclear fission reactors but it does not emit gamma ray when it decays. You need a liquid scintillator to count the beta particle from tritium decay.

will you be testing plants as well?

Submitted by ABH (not verified) on Sat, 2011-03-26 12:06.

I am curious about the cesium levels in milk and the plants that so many of eat from california (spinach, kale, carrots, etc).

Thanks,
ABH

This is unlikely to be an

Submitted by Anonymous (not verified) on Sun, 2011-03-27 19:13.

This is unlikely to be an issue, but we are beginning to test local milk.

milk from cows that are locally grazed

Submitted by Anonymous (not verified) on Mon, 2011-03-28 09:30.

I'm guessing you are already doing this, but when you test milk, will you be testing milk from cows grazed locally? (as opposed to cows that are fed grain shipped from other parts of the country)