[time-nuts] Re: ammonia, cesium, masers, etc.

[Perry E. Metzger]

The width of the line cannot be zero; it will depend on temperature, 
external fields, the isotope abundances of the atoms in the ammonia, etc.

Note that the precisely given frequency for cesium in SI units in the 
BIPM brochure comes with similar caveats:

"The second, symbol s, is the SI unit of time. It is defined by taking 
the fixed numerical
value of the caesium frequency, ∆νCs, the unperturbed ground-state 
hyperfine
transition frequency of the caesium 133 atom, to be 9 192 631 770 when 
expressed in
the unit Hz, which is equal to s^−1."

"The reference to an unperturbed atom is intended to make it clear that 
the definition of the
SI second is based on an isolated  caesium  atom that is unperturbed by 
any external field,
such as ambient black-body radiation."

Real quantum mechanical systems, of course, operate at non-negligible 
temperature and in the presence of external fields.

Perry

On 9/20/21 13:19, paul swed wrote:
> According to one of the articles 23,870,129.007 Hz +/- 10 Hz. That may have
> been the measurement limit at the time and the technology.
> Paul
>
> On Mon, Sep 20, 2021 at 1:15 PM Andy Talbot <andy.g4jnt at gmail.com> wrote:
>
>> What's the exact resonance frequency of ammonia?   To as many sig figures
>> as it's been calculated.
>> Googling just seems to throw up "approximately 23.8GHz"