We had a great visit! This was the first installation of a DoseNet device outside Berkeley. It was great getting the opportunity to talk to interested students, recruited by Ms. Eaton, about the project. We look forward to our next visit to meet with all the science teachers!
As a follow up to our recent measurements at Half Moon Bay, we wanted to quantitatively measure some of the samples we took along the beach. Previously, we found that mostly Uranium and Thorium isotopes were contributing to the increased count rate along the beach, and we wanted to measure the concentrations of these isotopes present in the sand.
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).
Three samples of Red Salmon from Alaska have been tested. The salmon was caught at the same location (the Kenai River) in July for each of the last three years-- 2011, 2012, 2013! A small amount of Fukushima-sourced radio-cesium was found in the July 2011 sample, likely from the initial airborne releases of radioactivity in Spring of 2011. No Fukushima-related radioisotopes were found in the 2012 and 2013 samples. In all samples, naturally radioactive potassium dominated the gamma spectrum. Bi-214 and Pb-210 are also naturally occurring radio-isotopes. Most of the Cs-137 originates from releases before Spring 2011.