This item contains backups of measurement data from the Safecast environmental monitoring project: https://safecast.org
From their webpage: "Safecast is an international, volunteer-centered organization devoted to open citizen science for the environment. After the devastating earthquake and tsunami which struck eastern Japan on March 11, 2011, and the subsequent meltdown of the Fukushima Daiichi Nuclear Power Plant, accurate and trustworthy radiation information was publicly unavailable. Safecast was formed in response, and quickly began monitoring, collecting, and openly sharing information on environmental radiation and other pollutants, growing quickly in size, scope, and geographical reach."
Files were downloaded from: http://blog.safecast.org/downloads/
The data is licensed under CC0 (aka, public domain, though attribution is expected).