Related to this, is it normal that radioactivity detector are not everywhere?
At least in the US there is also a pretty substantial network of teams and equipment for providing radiological technical support in an emergency. Examples of this are DoE RAP and the USNG CST. Now part of the motivation for this work was that a lot of the techniques for actually doing a search are fairly primitive, but there is a major support network with most of the tools and skills ready to go 24/7. It tends to all be very low key and fly under the radar, mostly because even a hint of one of these teams being deployed tends to cause a panic.
In fact, the house down the street to my parents' was torn down and rebuilt in the 80s because it had contaminated rebar.
When I was a kid, a neighbor, who is a civil engineer had a Geiger counter and went through the neighborhood and said he found nothing abnormal.
However, there is a cluster of cancer cases of people in the neighborhood of all kinds (breast, testicular, melanoma, liver, and kidney, of which my mother died of), including two friends who still lived there, and were diagnosed in their early 30s. Could be just bad luck, but I still wonder. My father still lives there.
I guess I should at least skim your dissertation, but is there a device that could be employed to sweep the neighborhood?
Still, it's a bit tempting to go check.
There is even a public realtime map.[1]
Also at least in Switzerland, all old metal scrap companys, waste incineration plant, and so on, have radiactive detectors on the entrance.
[1] https://remap.jrc.ec.europa.eu/Advanced.aspx
[Edit] It seems since April 2026, Switzerland has also a lot radioactive checks in border/customs control and bigger post/packet centres.
Radiacode detectors are about the only affordable detector with actually useful performance out there, and they are around $300. Which is also drastically cheaper than anything else out there, the next cheapest actually useful detector out there that I know of is 10x that price.
It's also normal that radiation can be detected everywhere (subject to terms and conditions with respect to sensitivity and sensing time).
The least radioactive places are just above the middle of large bodies of freshwater.
Still detectable there, just from very stray land sources, drifting airborne sources, and plucky cosmic sources that made it through the atmosphere.