[time-nuts] Is the lifetime of a Rb standard dependent on operating orientations

[cdelect at juno.com]

Hi,

At operating temperature the lamp, filter cell (if used) and the
resonance cell only have gaseous Rubidium in them.

Only exception is early designs that have a "stem" on the resonance cell
that exits the cavity.

There is a small amount of liquid Rubidium in the stem and in the 5065A a
thermoelectric cooler is used to set the amount of Rubidium that
eventually enters the cell.

No orientation problems an any Rubidium standards due to "puddling".

However if a 5065A is stored for MANY years or stored at an extended
period at high temperatures more Rubidium than desired can "flood" the
cell. At operating temp it's still pretty much a gas but too much in the
cell makes it opaque to the required light from the lamp. HP describes a
routine to deflood the cell if that happens.

Cheers,

Corby