The information comes from a strange source - the husband and wife comedian couple cum independent journalists attending and reporting on TEPCO and the government press conferences when they are not on stage.
In their blogpost on August 11 (in Japanese), they relate their talk with a researcher at the University of Tokyo who has submitted a scientific paper to a foreign academic society. This researcher, whom they say they cannot name because the paper is being reviewed right now, went to Fukushima and collected soil samples, rice hay samples, and water samples. He even went to the front of Fukushima I Nuclear Power Plant and collected samples there.
He also went to Iitate-mura. And he tells the couple that he found neptunium-239 in Iitate-mura, about 38 kilometers from the plant, in approximately the same amount as he found at the front gate of Fukushima I Nuclear Power Plant. That is the topic of his paper.
The couple says in the very intelligent post that they cannot provide details because the paper is in review (but they also say the researcher has given them permission to talk about it in general terms), but it was in several thousand becquerels. There is no mention of whether it was per kilogram or per square meter or per something else.
There is no mention of when the researcher went to Iitate-mura. I could be wrong but the indication from the post is that it was after the news that chlorine-38 detection at Fukushima I Nuke Plant was false. TEPCO retracted the earlier announcement of chlorine-38 detection, on April 20.
Uranium-239, whose half life is about 24 minutes, decays into neptunium-239 through beta decay. Neptunium-239, gamma emitter whose half life is about 2.4 days, decays into plutonium-239 whose half life is 24,200 years.
If this Tokyo University researcher went to Iitate-mura after April 20 and he was still detecting neptunium-239 whose half life is only 2.4 days, I just abhor to think of the implications. The locations that he found neptunium-239, in Iitate-mura and in front of the plant, were never tested by the Ministry of Education and Science or by TEPCO, according to the post.
Evacuation of Iitate-mura wasn't completed till late May, but not all villagers evacuated. There are still old people living in the village, and the villagers regularly go back to the village to check up on things.
I don't know how much longer Japan can continue to "Extend and Pretend", but probably much longer than anyone outside expects. We'll find out when this paper gets published.