[time-nuts] Quartz resonator aging - Vacuum backfill and getters

[Attila Kinali]

Moin,

I stumbled over one small question in my quest to understand quartz
resonator aging (and production). One is, that most people who mention
backfill of resonator packages talk about Helium backfill. Yet Helium
has quite high diffusion rate through metall (not as bad as Hydrogen,
but still noticable). While I doubt it would be a major factor in
aging, I keep wondering why not Neon? Neon is big enough that it has
no significant diffusion through metals while still retaining the
property of being non-reactive (until noble gases become reactive
enough to talk about, you need to go at least down to Xeon).
The only reason I could think of is, that Neon is too heavy, which might
lead to higher damping for the same thermal conductivity (pure guess,
I didn't do the math, nor did I find any references to this).
So, can the experts here englighten me, why nobody talks about Neon?

The second question I have is, why very few people talk about getters?
So far, I have found only one reference of getters being used in
resonator packages. With absorption being one of the major aging
mechanisms, I would have guessed that getters would be a big thing
in crystal resonator design. Why aren't they?


				Attila Kinali
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