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

[Bernd Neubig]

Hi,

>Attila wrote:
>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.

High precision crystals are usually under vacuum, no backfill of anything.
Same for tuning fork LF crystals, where any backfilling would deteriorate
the Q dramatically.
Practically all other crystals are backfilled with dry nitrogen  with a dew
point below -55°C.
Helium backfilling is used "on top" of the nitrogen backfilling with a
percentage of 5% to 10%. The reason for He backfilling is to allow a fast
fine leak testing in production with a He mass spectrometer. 
Without He backfilling the crystals need to undergo a storage in a He
pressure vessel for a couple of hours before being tested for fine leak.

Regards
Bernd