[time-nuts] Exact Rubidium frequency

Tom Van Baak tvb at LeapSecond.com
Sun Jul 1 10:12:28 EDT 2007

> Thank you all for your replies.  It still begs the question of why 
> NIST and PTB disagree by nearly 5 Hz on their web pages - I'll write 
> and ask them, and report back what they say.
> Regards,
> Peter Vince  (G8ZZR, London)


Yes, please send a note to NIST and have them update the
Rb hyperfine frequency that appears in:

My guess is the old ...608 number came from a 1959 paper:
  Hyperfine Transitions in Rubidium-87 Vapor

I suggest for the purposes of their glossary, the new number
doesn't have to be accurate to the micro-Hertz and probably
doesn't need to be changed every time someone does a new
experiment with Rb.

NIST gives the defined value for Cesium: 9,192,631,770 Hz
and a rounded value for Hydrogen: 1,420,405,752 Hz, so a
value of 6,384,682,612 Hz might do. Not sure what to say
about ...612.8 vs. ...610.904. Let NIST figure that one out.

Either way, I don't have to change my cars ;-)


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