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Originally Posted by N2IXK
Certainly possible, assuming you ran the tube in a helium-rich atmosphere.
This is the principle behind the helium leak detectors used on high vacuum systems. Helium atoms being able to diffuse through tiny cracks is certainly true. It often happened with early He/Ne laser tubes, but in the other direction, where the He slowly diffused out of the tube (through the epoxy seals), depleting the mixture of Helium until the laser stopped lasing.
A coworker once was able to rejuvenate one of those tubes by placing it in a chamber of pressurized helium for a while.
Some high speed counter (dekatron) tubes that included H2 or He in the gas mix were prone to issues as well.
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This is interesting. When we got our first high-def Saticon cameras, we were warned to fire them up for a while at least once every few months to get rid of accumulated gas. I never heard an explanation of where the gas comes from. Also, I'm guessing the cathodes in camera tubes were more susceptible to degradation due to being so small.