Rad101: Sources of Radioactivity in RadWatch Measurements

Still curious about radioactivity? Below we describe the different sampling and monitoring efforts that RadWatch is engaged in, why they are important and where the radioactivity comes from.

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.

Which isotopes would indicate Fukushima?

The reactor inventory in Fukushima contained many different radioisotopes, however there are very few that are both measurable and unique to Fukushima. Possibly the most likely isotope for proof-positive detection of Fukushima is Cs134 in significant quantities. This is because Cs134 is only produced in nuclear reactors from activation of beta-delayed reactor products. It also has a relatively short half-life. Other isotopes such as Cs137 are not positive indicators of Fukushima since it was also a product of atmospheric testing from 1945 to ~1980.