[time-nuts] Rb Oscillator - rather fundamental question

David C. Partridge david.partridge at dsl.pipex.com
Tue Feb 23 10:19:48 UTC 2010


Cough - the rubidium clock or oscillator does have an intrinsic frequency,
which is the rubidium hyperfine transition of 6 834 682 610.904 324 Hz, it's
just that the frequency generated by the transition in question isn't used
to DEFINE the second, so by definition, it must be secondary.  Only a
Caesium clock is a primary standard, as the second is DEFINED to be the time
taken for 9,192,631,770 cycles of the radiation corresponding to the
transition between the two hyperfine levels of the ground state of the
caesium 133 atom.[1].

Unless of course they changed the rules recently ...

[1] <http://www.bipm.org/en/si/si_brochure/chapter2/2-1/second.html>

Dave
-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Poul-Henning Kamp
Sent: 23 February 2010 09:53
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Rb Oscillator - rather fundamental question

In message <4B83A33C.1010903 at smiffytech.com>, Matthew Smith writes:

>Simple and rather fundamental question: does the common or garden 
>rubidium oscillator constitute an atomic clock?

Yes.

It is classified as a "secondary" atomic clock, because it does not have an
intrinsic physical frequency, like the cesium standards, but it is an atomic
frequency, and it is an atomic clock (if you attach a display or a pair of
hands :-)


-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
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Never attribute to malice what can adequately be explained by incompetence.

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