Try typing in :
"X-Rays", or "Radiation hazards" on a decent search engine. I did this a while ago and it presented me (amongst other things) with peoples thesis' on the subject you are talking about. In one instance they were reporting on the amount of rads individuals got, ranging from a Qantas air hostess (breast cancer) to airline pilots flying concord (brain cancer) and their increased probability of getting it because of their jobs!!!! Did you know that dependent on the latitude at which one flies you could get the equivalent of 1 chest X-ray each way when crossing from one continent to another!![at 35,000feet]. Worse for business jet passengers s at 40+ thousand feet.
Good hunting.
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TC