I guess it is some kind of problem with the home-made counter (e.g., picking up electrical noise), or perhaps the counter is placed in a building with a higher background level.
As far as I’m aware, buildings made of blocks containing coal power plant slag have a higher background, but I don’t know how pronounced the effect is.
The normal background should be like 15–25 counts per minute for majority of Geiger tubes.
Readit News
About the site itself: why would some of these measurements be that high? Especially the really high value in France and the one in Britain stand out.
As far as I’m aware, buildings made of blocks containing coal power plant slag have a higher background, but I don’t know how pronounced the effect is.
The normal background should be like 15–25 counts per minute for majority of Geiger tubes.
Perhaps if the discussion catches on, I can send the link to the website's owner.