[time-nuts] Rb lamp lifetime...
nhbbobb at gmail.com
Mon Nov 3 19:26:23 UTC 2008
Thanks for your PDF
> Message: 5
> Date: Mon, 03 Nov 2008 01:46:37 +0100
> From: Adrian <rfnuts at arcor.de>
> Subject: Re: [time-nuts] Rb lamp lifetime...
> To: Yuri Ostry <yuri at ostry.ru>, Discussion of precise time and
> frequency measurement <time-nuts at febo.com>
> Message-ID: <490E49ED.80906 at arcor.de>
> Content-Type: text/plain; charset="iso-8859-1"
> there are some interesting hints (including lamp rejuvenation) in the
> attached papaer that was posted here a few months ago by Gerald
> Molenkamp VK3FGJM.
> Yuri Ostry schrieb:
> > Hello,
> > Readed list archives and googled a lot, and seen two opposing points of
> > view - one is that there is nothing to age in Rb lamp, another is that
> > Rb lamp is degrading when in operation (without details, how and why).
> > I'm planning to get some Efratom Rb oscillator to use it in a
> > constantly running home lab frequency reference. Trying to understand
> > for myself, is it worth to get spare unit (or even two) of the same
> > model just to have replacement lamp on hand.
> > One more question - does someone seen Rb standard that is
> > malfunctioned due to degraded lamp, that, at same time, does have
> > good vacuum. If so, which model, and how the failed lamp looks like?
> > Was there any attempts to "rejuvenate" the lamp? (for example, heating
> > to remove glass darkening, if any, or similar experiments).
> > By the way, I'm very curious about physical process that may cause
> > lamp degradation.
> > Rubidium-87 that is included in the lamp (according to
> > manuals) is a radionuclide, beta emitter. It decays very slowly (4.7
> > billion years half life) to stable Strontium-87, emitting 282.62keV
> > electrons and (anti?)neutrino. I don't think that 87Rb decay may
> > interfere with unit operation after tens of years, unless 87Sr is
> > "poisonous" so much so it can interfere with lamp operation even in
> > tiniest amounts.
> > The only reference I located to date, is following article, that is
> > not available to general public. It is hard to understand for me just
> > from this abstract, does it specifically related to space environment
> > factors, or it is something that may cause degradation of Rb clocks
> > that is operated in average lab on Earth. ;)
> >> A Mechanism of Rubidium Atomic Clock Degradation: Ring-Mode to
> >> Red-Mode Transition in rf-Discharge Lamps
> >> Camparo, J. Mackay, R.
> >> Aerosp. Corp., El Segundo;
> >> This paper appears in: Frequency Control Symposium, 2007 Joint with
> >> the 21st European Frequency and Time Forum. IEEE International
> >> Publication Date: May 29 2007-June 1 2007
> >> On page(s): 45-48
> >> Location: Geneva,
> >> ISSN: 1075-6787
> >> ISBN: 978-1-4244-0647-0
> >> INSPEC Accession Number: 9805223
> >> Digital Object Identifier: 10.1109/FREQ.2007.4319027
> >> Current Version Published: 2007-10-01
> >> Abstract
> >> In the vapor-cell atomic clock, long-term stability can be
> >> influenced by slow variations in the discharge lamp's output via the
> >> light-shift effect. Additionally, over a multi-year mission lifetime
> >> the lamp's aging can degrade its optical pumping efficiency.
> >> Understanding the mechanism(s) that drives these changes is
> >> particularly important for spacecraft devices, where the atomic
> >> clocks are called upon to function continuously and reliably for
> >> many years. Here, we consider the two well-known, but little
> >> studied, modes associated with alkali rf-discharge lamp operation:
> >> the ring mode and the red mode. Consistent with previous research,
> >> we find that the ring mode is best for optical pumping, and that the
> >> clock-signal amplitude degrades significantly when the lamp operates
> >> in the red mode. Examining the emission spectrum as the lamp
> >> transitions between these two modes, we show that the ring-mode to
> >> red-mode transition is driven by radiation trapping within the lamp.
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