Seaweed Measurements (2013)

These seaweed samples were provided to our group by a seaweed harvesting company located in Northern California as a continuation of a study beginning in spring 2011. As in previous years, we tested the samples using a high purity germanium (HPGe) detector in Etcheverry Hall, UC Berkeley. HPGe detectors have very high spectral resolution, meaning they are able to distinguish the gamma-ray lines coming from different radioactive isotopes. For seaweed this is especially important because there is typically a large amount of the naturally occurring isotope potassium-40 (K-40).

The samples were counted for between 24-36 hours each in order to measure enough gamma rays to get good statistics. The results are displayed in the table below, expressed in units of Becquerels per kilogram, where one Becquerel is one nuclear decay per second. The weights used in the analysis are the “dry” weights of the seaweed.

No isotopes due to Fukushima have been found in these or any previous samples we have tested.

A table of these results is shown below.

Table of Results:

Species Location Date Harvested K-40 [Bq/kg] Cs-134 [Bq/kg] Cs-137 [Bq/kg]
Alaria Marginata Greenwood Cove 04/28/2013 1050 ± 100 N.D. (<0.20) N.D. (<0.20)
Porphyra Lanceolata McKerricken 06/11/2013 360 ± 36 N.D. (<0.085) N.D. (<0.14)
Postelsia Palmaeformis Medocino Coast 07/10/2013 870 ± 90 N.D. (<0.068) N.D. (<0.11)
Laminaria Setchellii McKerricken 07/22/2013 810 ± 80 N.D. (<0.12) N.D. (<0.13)

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