[time-nuts] Fw: Rb Oscillator - rather fundamental question

Lux, Jim (337C) james.p.lux at jpl.nasa.gov
Tue Feb 23 21:13:17 UTC 2010

> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of WarrenS
> Sent: Tuesday, February 23, 2010 1:04 PM
> To: Discussion of precise time and frequency measurement
> Subject: [time-nuts] Fw: Rb Oscillator - rather fundamental question
> One more try, As often happens when I rant, the rant is discarded in the
> posting.
> Rick
> Thanks, Interesting but maybe you have missed my too subtle of a point.
> Example:
> Lets say the second is redefined in the future to some new super duper thing
> that is good to 1 part in e20
> (Which will happen  if (when) the super duper thing becomes more available
> and proven)
> (Maybe based on the time it takes to count all the atoms in the new purposed
> 1 Kg sphere OR something like that.)
> Then the CS Osc would not be the BEST primary standard anymore, at least NOT
> at the new improved spec it could then be given.
> Not because it has changed or is less accurate, but because there is now
> something better.
> If it is not the primary standard, it does not make it worse, but it does
> mean it will now be a second standard at the new higher performance spec, by
> definition and need to be then calibrated and checked against the new
> primary standard IF one wanted to use it to it's maximum capability as a
> cost effective substitute for the supper duper.

I don't think so..

In that event, the unobtainium and Cs sources would both be primary standards (within their random variation).

The Cs+ standard would be less accurate than the Un+ standard, but they're both primary.

The key to a primary standard is that if you build it, it requires no calibration against something else.
It's like the meter, which is defined in terms of the wavelength of a particular spectral line in vacuum. Doesn't matter how you get the spectral line, but count off some number of wavelengths, and that's a meter.

Now, could one argue that a Rb source is also a primary standard, just with low precision?  

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