What are we detecting?We are detecting mainly two sources of radioactivity, naturally occurring radioactive materials (NORM) and technically enhanced radioactive materials (TENORM). These constitute almost 82% of radiation exposure for US citizens.
Please know that to date we have not detected isotopes from Fukushima Dai'ichi since 2012. The radioactivity that we detected just after the accident was in small quantities, which were measured in air and milk. As a summary of the previous measurements, we have never detected radioisotopes from Fukushima in quantities with measurable health effects.
These measurements are a continued effort of the initial environmental monitoring, for scientific curiosity and also for public outreach. As part of this we monitor NORM, TENORM and, if technically possible, place bounds on the concentration of isotopes that would be positive indicators for Fukushima.
Our measurements fall into two categories: those which are part of the Bay Area Environmental Sampling and those which may be used as References for putting those measurements into context. These two categories are divided into two tables for this distinction.
For those interested in why we commonly see these radioactive sources, above is a table of the origin of these radioisotopes.