Question for BRAWM team about "Americium"

Thanks for following up on this, Anonymous. I have been thinking about this, especially because the "hot particles" topic has come up recently again on the forum.

Our contact with Marco Kaltofen has been limited to the discussion below, but I did read his paper about the methods he uses to identify and quantify the particles. I think what we are doing is so different that we really can't say anything scientifically about his methods and data. But it is also not clear what the magnitude of the risk would be.

Here are the long versions of those thoughts:

(1) Our sampling and analysis methods are very different (see Marco's methods paper), the questions we are asking are very different, and the risks of each type of radiation are very different. We at BRAWM have been looking for tiny air particles with small numbers of fission isotope nuclei attached to them. The WPI research is looking for tiny particles each made up of lots of radioactive atoms. The health risks of each are different. The fission product isotopes disperse throughout the environment, and that is why they can be dangerous (they get in our food) and also why they can be not dangerous (they get dispersed). These "hot particles" would be almost the opposite — their danger would be because they are concentrated into one mass that can irradiate a small amount of tissue around it for a long time, while the particles themselves are relatively few and far between.

(2) BRAWM should be sensitive to some of these particles, such as Americium-241. We would not be sensitive to particles of plutonium, and only marginally sensitive to particles of uranium. So I don't think our data would be particularly helpful to corroborate those findings, except for perhaps determining limits for Am-241. So we cannot really say anything scientifically about this.

(3) So as a scientist who cannot say anything scientific about the results, then I am left wondering what the data mean. It is reported that we could have been inhaling 5 hot particles per day on the West Coast, but what is the magnitude of the risk if that was true? It is very possible that this issue has been overlooked as an important health concern, and it is also possible that it is not much of a health concern at all. I don't think this problem lies with Marco's study; it seems like there's just not that much known. This topic is worth further study and more data.

Mark [BRAWM Team Member]

Marco,

Thank you so much for visiting and helping us learn more about the testing you have been doing. Yes, the types of testing we are doing are quite different and we can learn a lot from both.

From reading your paper it appears that isotope identification is done primarily through the use of X-ray fluorescence, and so the elements you detect that you can also conclude are radioactive are limited to those which have no stable isotopes (i.e., anything heavier than bismuth). So are the radioactive particles you detect limited to those heavier particles? You seem to mention detecting iodine and cesium, so I'm curious if you've also done some gamma spectroscopy.

I am also curious about your samples. How are they collected -- in air filters? Where in Japan and the US were samples taken?

What kinds of particles have you detected Americium in? Are they small enough and mobile enough to be consistent with transport across the ocean? Also, has Americium been detected in samples from before Fukushima? Since it has a 433 year half-life, I would wonder whether the source is certainly from Fukushima or from something else. What are the amounts of Americium being compared to, such that the amount detected is consistent with nuclear fuel?

As for our measurements, we exclude any activity from Am-241 above about 3E-9 Bq/L (pre-4/19) and 1E-9 Bq/L (post-4/19) in the air. However, as you point out, your measurements and our limits are would be difficult to compare.

Mark [BRAWM Team Member]