We are getting a lot of questions, both at email@example.com and through the Safecast group from concerned people – they all try to understand some aspect of radiation or another. And of course, many people ask similar questions, but without doubt the most often asked question is “Is [something] safe?” or a variation of it. Believe it or not, there is an answer in our radiation FAQ, but people keep asking
Recently someone who was planning to spend a few months in Kyushu asked about the contamination there. He had located some info on the radiation levels, and had concluded that currently the radiation level is higher than before 3/11. He asked if that was because of Caesium and Strontium contamination. In fact, he was comparing two different data sets that had been collected differently. I pointed him to DPNSNNE which allows users to download consistent monitoring data from all over the country and compare the changes over time. This data shows that aerial radiation levels in Kyushu are the same now as they were before the accident. As often happens in forums/mailing lists, once the question was answered, the discussion shifted the topic to “the difference in risk from Radon (naturally occurring) compared to Caesium and Strontium (anthropogenic)”. Immediately, data on half-lives (=time that it takes for the half of a certain amount of a radioactive isotope to decay) of Rn, Cs-137, Cs-134 and Sr-90 was put on the table as “evidence” and difference between half-life and biological half-life was discussed. So the question transformed into:
- Since the (radiological) half-life of Radon is only 4 days, while Cs-134/137 has a biological half-life of 70 days (that is, half of it will be eliminated from the body in 70 days), and Strontium’s is 18 years, doesn’t that mean that radon is less risky than the others?
I had been thinking about this a lot and thought I might be able to explain it by example; an example that turned into this blog post (Here is a good place to thank Azby, Jam and everybody who read through my ramblings and pushed me to publish it).