Following up this article..Black substance mass generated
Though you can’t see the black substance, Mr. Oyama koichi measured alpha nuclide from the cover of the street gutter in Iwaki shi. (Alpha ray survey meter TCS-232)
From this video, you can’t tell the alpha ray level, but they measured it without a sheet of paper.
They turn over the cover and measure it again but they don’t catch anything.
Upside of the cover
- With a sheet of paper : Nothing detected
- Without a sheet of paper : alpha ray detected
The other side of the cover
- Without a sheet of paper : Nothing detected