[ntp:questions] Re: Use of "Atomic Clock" Nomenclature

David L. Mills mills at udel.edu
Sat Jan 21 17:47:56 UTC 2006


I have three Cs oscillators here and have on occasion transported them 
to USNO in Washington DC for recalibration. I put them in the back of my 
wife's van; she drove to USNO and a worker dashed out of the building 
with a cable carrying UTC(USNO). The self-contained batteries run the 
thing for twenty minutes; an auxiliary battery pack runs it for many 
hours. Power for my wife's van comes from an inverter and van's battery.

I have a log for one of these devices that has been all over the world 
since the early 1970s when it was shipped by commercial air as a first 
class passenger. Maybe ten years ago the DoT got serious about 
transporting these things and I had to get an approved shipping 
container to send the devices for Cs tube replacement.

There is a story that HP (Agilent), in a bid to convince DoT the devices 
were safe to ship, tossed one out the second story lab window onto the 
parking lot. You have to see and handle one of these things to 
understand how massive and rugged they are. I suppose it made a serious 
hole in the pavement. Anyway, DoT now allows shipment by conventional 

If you have ever seen a tiny bit of Sodium hit water, you might expect a 
tiny bit of Cesium to do the same. The stuff is indeed mildly 
radioactive, but so is the waste nuclear fuel now transported by convoy. 
In any case, my devices are seriously labeled as "cesium oscillators," 
not by any way, shape or means as "atomic clocks."

The best story I have is a report that, during a stopover at Roma 
Fiumicino Airport (now Leonardo da Vinci Airport), the battery pack was 
about to expire and the accompanying passenger needed to find power to 
recharge. A skeptical airport manager finally agreed, but upon 
connection the charger blew the circuit breaker. I have no report of the 
ensuing actions, but it does show that a Cs oscillator with discharged 
batteries might as well be tossed out the window.

Quite frankly, there is no need in present society to ship Cs devices by 
air, unless to deliver a newly manufactured unit. I calibrate mine by 
GPS probably as precise as the lab worker at USNO. We have two-way 
satellite transfer between laboratories and no longer need LORAN-C for 
that purpose. For that matter GPS has replaced my need for Cs devices in 
the first place and, after all, the tubes don't last forever and cost 
several thousand bucks to replace, even with used tubes.


Richard B. Gilbert wrote:
> fm at nowhere.invalid wrote:
>> Ulrich Windl <Ulrich.Windl at rz.uni-regensburg.de> wrote:
>>> "Max Power" <mikehack at u.washington.edu> writes:
>>>> Use of "Atomic Clock" Nomenclature
>> <snip>
>> It seems that Cs clocks are  now  forbidden  to  fly
>> because cs133 is highly flamable (or  even  does  it
>> burn spontaneously ?) in the ambiant air.
> Cesium belongs to the same chemical family as Sodium and Potassium.  It 
> will burn spontaneously when exposed to air and/or water!  I would be 
> surprised, however, if the amount of cesium in a cesium beam tube were 
> sufficient to be serious problem.  And if I were shipping a cesium beam 
> tube or an entire cesium clock by air, I would take extreme care in 
> packing it.  I'm told that the cheapest cesium clocks cost about $40,000 
> US.

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