Canadian testing results and questions for Mark

Very interesting to hear about those tests. You raised a number of questions, so I'll try to address them all:

1. As no Cs 134 was detected, can we assume that this is not likely Fukushima-related?

   Due to the particular burn-up characteristics of the Fukushima reactors, the Cs-137 to 134 ratio should be approximately 1:1. We saw this in our air and water samples. When we started measuring soil samples, we at first saw a 1:1 ratio but then measured some samples with higher ratios, like one with a ratio of 30:1. The excess Cs-137 cannot be from Fukushima because Cs-134 should also be there in the same amount. The excess Cs-137 must be that which was deposited by weapons testing decades ago, which dispersed trace amounts of fission products all over the world.

2. Is it physically possible that alpha-emitting fission products/ isotopes from Fukushima made it to Canada without the detectable presence of radio Cesium or Iodine?

   No, I would not expect to see alpha emitters without seeing Cs-134 and Cs-137. The vast majority of materials that were released from the Fukushima reactors were the very volatile fission product isotopes I-131, Cs-137, and Cs-134. (By the way, all fission products are beta and gamma emitters; no fission products are alpha emitters.) Any alpha emitters in nuclear fuel are actinides like Uranium and Americium, but on the whole these are not volatile. When compared with the iodine and cesium isotopes, actinides could only have been released in extremely trace amounts.

3. However, one concern is over gross alpha radiation (several hundred Bcq/ kg) in two soil samples, and detectable alpha radiation in rain, snow and drinking water.

   Alpha radiation is very common in nature. There are many naturally-occurring alpha emitters — the ubiquitous Uranium-238 and Thorium-232 decay chains each contain several isotopes that emit alphas. One example is Radon-222, one of the isotopes of radon gas, which is produced from the decay of U-238 in soils and minerals.

   One discussion you might be interested in on this forum is a question some farmers had about gross alpha and beta measurements of soil samples. They were surprised at the levels of gross alpha and beta counts — they saw a few hundreds of Becquerels per kilogram. To help understand how that could be, I took our gamma-ray measurements of soil and used the isotopic information we get to infer what the gross alpha and beta should be for our samples. I calculated that the average gross alpha we had was about 170 Bq/kg, and our handful of samples fell in the range 50–370 Bq/kg. This variation is simply caused by the large natural variations in the content of U-238 and Th-232 in minerals. You can read the discussion here.

4. Any advice on how/ where it would be possible to do further testing on these samples?

   I do not have any specific recommendations, just that the lab be equipped to perform alpha spectroscopy and have the radiochemistry necessary to prepare samples. However, I don't think there is anything to worry about. You would only end up finding that nature provides a great deal of alpha radiation already from the ≈ 14 alpha emitters in the U-238 and Th-232 decay series. Any non-natural sources, whatever their origin, would only be trace amounts.

Mark [BRAWM Team Member]