How much ionizing (carcinogenic) radiation is one exposed to on a commercial flight, what are the sources, and how could exposure be minimized? I don't know if this is the best place to ask this question, but I figure a physics-based answer would be the most satisfying. I'd be happy to be convinced I'm being paranoid about protecting an infant from such increases in radiation too.
I'm wondering about radiation that could directly or indirectly mutate DNA sequences (X-rays, UV, gamma?).
I'm also wondering about feasible strategies to minimize this exposure  (particularly for preventing exposure to an infant). Would BoPET (Mylar) blankets or aluminum foil reflect such radiation? Would any material (that could feasibly be used to cover an infant) absorb the most problematic wavelengths?
Is the radiation at ~40,000 feet isotropic? Could there be some clever way to choose seats and orientations of any barriers (placing an infant between two parents?) to minimize exposure?
 A: background radiation is very dependent on where you live it's different depending on altitude rocks around where you live ect. but generally comes to around 0.1 - 2 micro sieverts per hour the "ionizing radiation regulations 1999" states: 


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*Anyone under 18 should not be exposed to more than 6 milli sieverts per year above background radiation ~ 1 micro sievert per hour.

*An unborn fetus should not be exposed to more than 1 milli sievert for the duration of pregnancy above background radiation ~ 0.3 micro sieverts per hour.


A flight can add a temporary increase in radiation exposure to up to 5 milli sieverts per hour but for a single flight this will have a lot less impact than simply living in the wrong place for a week. It's also worth noting that all of these regulations are several orders of magnitude lower than the lowest radiation exposure linked to any increased chance of cancer or radiation related illness. If you fly very regularly you might you might go over the sugested limit but a one off wont make a difference.
