February 16, 2015
What we found:
The absence of any detectable 134-Cs (an unambiguous fingerprint isotope of Fukushima contamination) in the seawater samples indicates that as of November 2014 these locations covering the length of the British Columbia coast have not be affected by ocean currents carrying Fukushima contamination.
The detection limit for 134-Cs averages ~0.2 Bq m-3
Newly added results come from seawater samples collected in collaboration with citizen scientists at the following locations in British Columbia, Canada during November 2014.
Samples were processed and the amount of gamma emitting isotopes determined using a high purity germanium detector. We look primarily for radioisotopes of cesium (134-Cs half life ~2 years and 137-Cs half life ~ 30 years) for the following reasons:
- 134-Cs has a half life that is short enough that all other human sources to the environment have decayed away making it an ideal tracer for Fukushima contamination
- next to the short lived Iodine-131 (half life ~ 8 days), Cs isotopes were released in greatest activity to the environment from Fukushima and would be most likely to represent a radiological health risk given their chemistry and propensity to be taken up by the biota
- other isotopes were released in much lower amounts from Fukushima relative to Cs (see other posts here and search for plutonium and strontium for example) and would therefore be much more difficult to detect
- because they are gamma emitters (unlike Pu isotopes and 90-Sr which emit alpha and beta radiation respectively) they are relatively easy and resource efficient to detect
The absence of detectable 134-Cs indicates that waters near these locations spanning the length of British Columbia have not been contaminated with Fukushima radioactive elements transported across the Pacific by prevailing currents as of Nov 2014. The presence of 137-Cs is due to historical sources of this human made isotope owing to atmospheric nuclear weapons tests in the 20th century and contamination from the Chernobyl disaster in 1986. You can read about the levels of 137-Cs in the North Pacific pre-Fukushima here.
More results will be published as they become available.