Seems they have photographed the x-rays...
X-rays from lightning photographed
and from 2009..
Mysterious Radiation May Strike Airline Passengers | LiveScience
passengers and crew members could be exposed to harmful levels of radiation, a dose equal to that of 400 chest X-rays.
However, the likelihood of encountering these lightning events is very small, the researchers say.
and from 2003..
X-Rays Abound When Lightning Strikes: Scientific American
They succeeded in harnessing 37 individual lightning strokes, and found intense bursts of x-ray radiation--each typically depositing tens of megaelectron volts into the detector--associated with 84 percent of them.