[time-nuts] Irradiated crystals

[Robert Atkinson]

Cost is unlikely to be an issue. Cobalt 60 gamma irradiation is routinely used to sterilise low cost disposible items. Even a one-off package would only cost around $100, not much in the scheme of high performance oscillators. It certainly produces changes in some materials, I can tell the difference between irradiated and un-irradiated polystyrene by eye.
   
  Robert G8RPI.  

Bernd T-Online <BNeubig at t-online.de> wrote:
  Hi all,

Murray Greenman wrote:

> ...I would imagine one of the reasons for
> the limited use of the gamma ray technique is cost.
> 
The irradiation is not done to get an ultimate aging, but to make such 
crystals more insensitive to the stronger gamma radiation (as mentioned 
in an earlier post).
In addition, quartz material used for space-qualified oscillators is 
undergoing a so-called sweeping process, in which a high electrical D.C. 
field is applied to the quartz block (which is metallized with gold on 
two opposite surfaces), while the crystal is stored at elevated 
temperature and the D.C. current is monitored. The current decreases 
over time, and after a few days or weeks, when the current has gone down 
below a given limit, the sweeping procedure is stopped. This process 
removes foreign ions from the crystal lattice and makes therefore the 
crystal more insensitive to irradiation. With the mentioned additional 
gamma irradiation of the crystal unit, remaining ions are further 
"removed" and thus the crystal becomes more immune against space radiation.

Regards

Bernd Neubig
DK1AG

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