M.C.
There is a great risk this will diversify into a new topic; but, I had an American on the jump seat who went ashen we we levelled at 390. He spoke about above FL290. I know there was an in depth study conducted by the unions of Germany & Italy. On a LH B747 they carried an expert from the agency that monitors radiation in factories etc. It said that his meter went off the scale at cruise FL. This was in mid 90's. It also said that LH was ordering all new a/c to have lined cockpits, but it would be too heavy for the cabin. In otherwords they recognised a risk. Nothing entered the public domain. Under the carpet, I feel. Can't do anything about it, so don't tell anyone.
Since then I've read very little, except that which was issued by a later employeer saying there was no risk. HM?
Perhaps if we want to discuss this, a 'new topic' would be the correct place.