I've been fishing around looking for info on the details of geiger tube manufacture - I might want to make some. I kind of hit paydirt with this paper - more than you would think about geiger tubes, quenching gas mixes, special purpose tubes, and so on - it's a pretty extensive report at over 12 megabytes. Enjoy!
No where else have I found this level of detail. If one wanted to go into the geiger tube business, this is the one you need - it even includes life data and issues with various quenchants, the underlying theory in detail, materials issues.