Recently, corresponding author Marco Kaltofen* (Worcester Polytechnic Institute), co-author Maggie Gundersen** (Fairewinds Energy Education) and I published our second peer-reviewed journal article analyzing hundreds of radioactive samples from northern Japan that we collected with assistance from Japanese citizens and scientists. Our sampling on five occasions over almost a decade totaled 70 days on the ground. Here are four things we discovered.
1. Existing radiation maps ignore significant sources of radiological exposure.
Most of the radiation maps of northern Japan are based on external radiation detected in handheld instrument measurements by citizens and scientists, who then link the measurements to GPS coordinates while downloading that data into a massive database. This information about direct, external radiation is certainly important, but it has become the de facto criteria for decision makers in Japan to decide which cities and towns should be repopulated.
We found that this approach only provides limited policy alternatives and serves to minimize potential population exposure for two reasons. First, the Geiger counter data is for external radiation that was deposited on the ground external to human bodies and ignores radiation imbibed or inhaled as “hot particles” into the human body.
Secondly, the external radiation data frequently displayed for northern Japan is based on radiation emitted from only a single radioactive isotope, Cesium-137 (Cs-137), as measured externally. On the other hand, our papers show a wide variety of isotopes that are not detected by handheld Geiger counters or absorbed externally. We show that there is an extensive brew of various isotopes present in radioactive dust that is inhaled or imbibed. Our papers indicate that the radioactive concentration in these dust particles varies widely, by a factor of 1 million, with 5 percent (3 sigma) of these “hot particles” 10,000 times more radioactive than the mean. Our most radioactive dust particle was collected 300 miles from the site of the meltdown.
Furthermore, the data show that alpha, beta and gamma-emitting contaminants in radioactive fallout from the Daiichi meltdowns have not traveled together in lockstep. This means that measuring only beta-emitters like Cesium-137 or only total gamma (as you would with a Geiger counter) is not enough to map the full impact of the fallout. Alpha-emitters must also be measured to protect the public health. This is especially important because of the serious health impacts that can come from exposure to alpha radiation.