On Thu, 26 Jul 2007 21:50:07 -0700, "Chuck Guzis" <cclist at sydex.com> wrote: Activated getter works on active gasses (and some of the heavier inert ones also) up to the point where the activated surface becomes saturated. In a well sealed tube, that can be a substantial time. However, it does not work with helium. Helium abhors a vacuum and will attempt to equilibrate its partial pressure inside the tube with that outside - glass and getter be damned. Same goes for HeNe lasers - the helium inside makes for the outside world and the laser goes south. I've been keeping a pair of HP Interferometers going for years by occasionally putting them in pure He for several weeks, all the time measuring the output and waiting for it to come back to spec. If you have an old, well-sealed tube that has gone gassy due to helium, you can rescue it by putting it in a high vacuum for a couple of months... CRC