I was born in the city where this happened, right on the US border: https://en.wikipedia.org/wiki/Ciudad_Ju%C3%A1rez_cobalt-60_c...

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?

The cheapest worthwhile detectors out there are the Radiacode ones. They are excellent for what they are, but they run around $300. Cheaper Geiger counters are unfortunately kinda useless, at least for this. It's also not particularly easy to know what you're looking at and how to interpret it even with a good detector, unfortunately I'm not sure how much luck you'd have so don't waste $300.