Re: H-3 Exit Signs

[jatalbq@ix.netcom.com (Joseph A Tompkins )]

Exit signs in aircraft are all of the gas filled variety.  The reason 
they do not leak is that glass is an excellent barrier against tritium 
diffusion.  The problem with tritiated polysytrene is that most 
tritiated organic compounds are not structurally stable.  The change in 
the molecular structure is evidenced by darkening of the polymer which 
generally reduces light output.  Work on non-darkening tritiated 
polymers was conducted at PNL and also at Amersham.  These tritiated 
polymers have not yet been demonstrated in a commercial application.