2 planes contaminated with radiactive 'stuff'

having found a radioactive trace on 2 planes on the Moscow/London route , one has to wonder about this revelation .
Po is very energetic and could irradiate secondary material it's true . However the primary radiation emmission is alpha and so cant really penetrate even a piece of paper very easily . Thus , if this radiation found came originally from a Po source then it would have needed to be naked and if so would have been a serious health hazard not east to the courier [ who may not have made it to the rendezvous - which obviously didnt happen].
Secondly the lethal amount of material is less than a microgramme - it would have taken 1 courier only , so why 2 ? [ unless there's another target ? ] - sending 2 couriers in case one got caught just doubles the chances of one getting nabbed so that would nt be credible either . So if true there would be 2 targets - watch the news to see if this pans out.....
A more likely reason is this : Planes tend to fly at high altitudes [ the 10 mile high club springs to mind] . At this altitude they tend to get hit inordinately by high energy radiation much more so than at ground level and so would be much more likely than ground based objetcs to become in some parts mildy radioactive [ and from the quantities they are looking for , it couldnt be much above background levels] . It would be interesting to find what percentage of planes throughout the world have a small area which is slightly above background levels .
Someone somewhere is overreacting ----- or someone has been smuggling other stuff in the past ------ ouch ......