On 02/20/2017 11:44 AM, John Rehwinkel wrote:
> Both effects happen: the neon and argon leak out because even though > they're at lower than atmospheric pressure, they're higher than the > partial pressure of neon and argon outside the tube. And, more > intuitively, oxygen and nitrogen leak in. Both of these effects are > detrimental to the tube's operation. Yes. The uber-killer, though is helium. It goes through soft glass like water through a paper towel. At one nuclear plant where I was setting up their radiation monitoring system, I suddenly started losing photomultiplier tubes in liquid and gas monitors. I traced the problem down to another contractor doing helium leak tests on the monitors (why? they operate at atmospheric pressure) and instead of the normal procedure of hooking the mass spec up to the detector and then flooding the monitor with helium, they were pressurizing the detection chamber and sniffing with a probe connected to the leak detector. I'm talking about exposure of just a few minutes. > > Old-style frit (or "soft") seal helium-neon laser tubes have a > similar problem. The helium (a very slippery gas) would slowly leak > out through the seals, so although the tube would still ionize and > glow, laser action wasn't supported. The cure is surprisingly > simple: "soak" the tubes in a trash bag with helium in it at > atmospheric pressure. With the reversed (and much larger) partial > pressure difference of helium, a few years' loss could be restored in > a few days. The normal setup was to leave the tube running and > monitor the laser output. It would slowly rise, then begin to drop > when the helium pressure began to get too great. Take the tube out > of the bag then and you could get a few more years out of it. I've done several of those. Amazing how fast the He goes back in. > > In short, you don't need a hyperbaric chamber, atmospheric pressure > will probably suffice, but you'd want to have the proper ratio of > gases. Just heat-seal the tubes in metallized mylar bags, the same stuff that modern helium balloons are made of. And keep helium out of your house! No helium balloons or whatnot. I'll bet that if one did a spectroscopic analysis on the light coming from a weak tube, one would see He in the mix. John -- John DeArmond Tellico Plains, Occupied TN http://www.tnduction.com <-- THE source for induction heaters http://www.neon-john.com <-- email from here http://www.johndearmond.com <-- Best damned Blog on the net PGP key: wwwkeys.pgp.net: BCB68D77 -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/c736a2e9-7d09-494b-cff5-53fca0e2054f%40neon-john.com. For more options, visit https://groups.google.com/d/optout.
