SimplyInfo has a new item about radioactive contamination of seaweed off Washington state:
New testing done by Worcester Polytechnic Institute, Dept. of Civil and Environmental Engineering found Fukushima cesium in US Pacific sea weed. The samples were standardized against a known amount of cesium 137 and cobalt 60. The finding of cesium 134 would indicate this is at least partially from the Fukushima nuclear disaster.
“Washington State Pacific coast eel weed sample contained 0.22 pCi/g of Cs134 and 0.24 pCi/g of Cs137. It also contained 0.1 pCi/g of Co60”
These values converted to the more common bq/kg are:
Cesium 134: 8.14 Bq/Kg
Cesium 137: 8.88 Bq/Kg
Cobalt 60: 3.7 Bq/Kg
I have not been able to get more information as to when the sample was collected and tested, only that this is a “new” test.
The significant thing about this measurement is that the amount of cesium-134 is 92% of the amount of cesium-137. This corresponds approximately to the ratio of 134 to 137 that was found in March 2011. Values of samples collected today contaminated with March 2011 fallout only would indicate 134 levels to be less than half of 137. Therefore this is new fallout.
Caesium-134 has a half-life of 2.0652 years. It is produced both directly (at a very small yield because 134Xe is stable) as a fission product and via neutron capture from nonradioactive Cs-133 (neutron capture cross section 29 barns), which is a common fission product. Caesium 134 is not produced via beta decay of other fission product nuclides of mass 134 since beta decay stops at stable 134Xe. It is also not produced by nuclear weapons because 133Cs is created by beta decay of original fission products only long after the nuclear explosion is over. (Wikipedia)
This would indicate that the seaweed sample has undergone atmospheric contamination from a recently emitted plume, that originated as a result of fission or a criticality.
The presence of cobalt-60 implies a criticality has occurred:
Cobalt-60, 60Co, is a synthetic radioactive isotope of cobalt with a half-life of 5.27 years. It is produced artificially by neutron activation of the isotope 59Co. (Wikipedia)
Cobalt-60 is an activation product which is produced from activation of cobalt-59 by free neutrons.
Again, I do not know the provenance of this result, so take this for what it is worth.