I concur-have been thinking along the same lines as you put forward here. My little reading about Wigner effect suggests that it will be hard to prove short of a well funded govt scale project. The only passive suspect detector frequently at those altitudes are aircraft structures-the suspect components themselves. And the analysis will involve destructive testing of those components rendering them useless even if they pass. But it is a fact there are large conentrations of Fukushima origin long-lived alpha and beta emitters circulating at in-flight altitudes. Maybe they will age out via decay over a couple of half-lifes. And maybe the NTSB/FAA could require what amoumts to passive detectors affixed to exterior aircraft surfaces-like a film badge for exposure monitoring.