Soil and manure samples, and detection of Cs-137 in soil from weapons testing fallout (9/6/2011)
9/6 (5:26pm): We tested a topsoil sample and a dried manure sample from the Sacramento area. The manure was produced by a cow long before Fukushima and left outside to dry; it was rained on back in March and April. Both samples showed detectable levels of Cs-134 and Cs-137, with the manure showing higher levels than the soil probably because of its different chemical properties and/or lower density.
In addition, a soil sample from Sonoma county was tested. This sample had been collected in late April but we had not had the chance to test it until now.
One interesting feature of the Sacramento and Sonoma soil samples is that the ratio of Cesium-137 to Cesium-134 is very large — approximately 17.6 and 5.5, respectively. All of our other soil samples until now had shown ratios of between 1 and 2. We know from our air and rainwater measurements that material from Fukushima has a cesium ratio in the range of approximately 1.0 to 1.5, meaning that there is extra Cs-137 in these two soil samples. The best explanation is that in addition to Fukushima fallout, we have also detected atmospheric nuclear weapons testing fallout in these soils. Weapons fallout contains only Cs-137 (no Cs-134) and is known to be present in older soils (pre-1963). Both of these samples come from older soils, while our samples until this point had come from newer soils.
This direct comparison between Fukushima fallout and atmospheric weapons fallout in these soils shows that the fallout from Fukushima in Northern California is significantly less than the amount of Cs-137 that still remains from weapons testing, which has had nearly 50 years to disperse and decay.
Mark [BRAWM Team Member]