NASA’s U-2 spy plane found gamma rays in 90% of lightning storms

[Marlin]

NASA's U-2 spy plane found gamma rays in 90% of lightning storms

https://www.popsci.com/environment/gamma-ray-lightning/

[Mounder]

3281' for ideal max travel of a gamma ray. So at 72,000 feet, it's only an AF dosimetrist/HP problem.  One more chip for the dosimeter to keep them busy. 
https://aviationweek.com/business-aviation/cosmic-radiation-exposure-polar-flights-part-1