James20k

Please be satire please be satire

By physical trace, they don't mean conclusive evidence of ufos, but that there is definitely physical concrete evidence of something. In this case, radiation is abnormal and shows something. Not necessarily ufos, but it's physical evidence

Background radiation doesn't vary enough for this to be a big problem (even hiroshima isn't that much more radioactive than background today, its something like 2x the upper end of background), and you can guess it based on the local area. In this sort of case, I imagine they find levels which are drastically higher than usual, and that lets you rule out background radiation as a cause. Obviously you'd check for local contaminants etc

eh, we love it for the drama, everyone knows the medicine is a bunch of made up words sellotaped together

Of course, nobody here is arguing that it is definitely aliens. UFOs are any unidentified flying objects in this case

who the heck says UFOs leave radiation in their wake anyway?

According to OP, there are cases of sightings of UFOs (generic flying thing) which involve abnormally high levels of radiation left behind in that specific case. Now, that doesn't show of prove or allude to anything, no, but abnormal levels of radiation and odd reports by witnesses are certainly worth investigating (this is science). Particularly combined with various EM sensors being tripped, that means there is something there, we just don't understand what it is yet

Hell, nobody believed in ball lightning until recently (just ufo fanatics seeing things!), but turns out that its a real phenomenon. We have no idea what's going on here whatsoever, and while some people say its aliens, according to the evidence there's unexplained things happening intermittently and nobody knows why. It could be some natural thing we don't understand, or whatever, so that's why its being investigated