[time-nuts] a link to a explanation of Rb vs Cs?

Richard (Rick) Karlquist richard at karlquist.com
Tue Apr 11 18:15:27 EDT 2017

The "magic" of Rb in a gas cell standard is that you
can make an optical filter cell out of radioactive
Rb87 isotope that allows you to selectively optically pump
to the quantum level you need.  It is just "luck"
that the absorption line falls where you need it.
And the RF pumping is at a doable 6.8 GHz.

I think the CSAC uses lasers so all of this doesn't

Cesium of course is part of the definition of the second,
so it's good to use for that reason.

It is a different discussion as to why Cs was chosen
to define the second, but the line being at 9.2 GHz might have had 
something to do with it.  That's a doable frequency in terms
of technology 60 years ago.

Rick N6RK

On 4/11/2017 1:54 PM, jimlux wrote:
> On 4/11/17 12:34 PM, Attila Kinali wrote:
>> Hoi Jim,
>> On Tue, 11 Apr 2017 07:30:38 -0700
>> jimlux <jimlux at earthlink.net> wrote:
>>> I'm looking for a link to point to an explanation (at a basic level) of
>>> the difference between Rb and Cs references, and what the tradeoffs are.
>>> I googled a bit, but all I got were some explanations of the differences
>>> in things like vapor pressure, etc.
>> What exactly are you looking for? A comparison of Rb vapor cell
>> standards vs Cs vapor cell standards? Or a general comparison
>> why different kind of standards are built with Rb and Cs?
>> For the former, there is a paper that has some of the details
>> why Cs was choosen over Rb for the CSAC in one of the papers.
>> (Which I currently cannot find...)
>> For the latter, there is no easy answer and a lot come from
>> technicalities (difference in handling) and what people were
>> able to build. There are some fundamental differences in which
>> elements get you what kind of stability for different kinds of
>> atomic clocks, but I have seen very little on that and it's quite
>> spread over various papers and books.
> precisely why I asked..
> The wikipedia article isn't bad in terms of covering the gas cell vs
> beam in words, but I was hoping for something with pictures..
> Encyclopedia Brittanica, perhaps.. except that they only talk about
> caesium beam
>>                 Attila Kinali
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