[time-nuts] Question for the cesium nuts.

Tom Van Baak tvb at leapsecond.com
Fri Mar 16 15:32:28 EDT 2007


Jack,

You bring up a good point, but...

The Cesium atoms make a one-way trip from one end of
the tube the other; from a nice solid/liquid pool of silvery
cesium in the oven to a splattered mess in the getter. So
there's no restoring the tube that once that's done. Think
toothpaste. Think ballpoint pen. Think taxes.

True, some tubes will last 20 years or more; and that's with
continuous use. If you only turn on the Cs once a week or
once a month to re-calibrate the excellent low-drift internal
OCXO inside your frequency standard then it will likely live
longer than you will. So it sort of depends on how you use
your valuable instrument.

I had nice pictures of the insides of a modern cesium tube
on my web site but was asked to remove them. But it's not
like the atoms make a nice trip from point A to point B and
when they are all at point B you simply wipe clean point B
and reload point A.

You can open a dud cesium tube without too much worry.
Any elemental cesium is still frozen in the oven. The rest
has been sucked up in the getter or is painted all over the
EM or magnets. Safe enough to handle (well, then again,
as many of you, I played with mercury as a kid).

As for time value of money, consider that owning, or having
access to, precise time is simply a service and you get what
you pay for. For example, if you want time to the hour it is
free -- look up at the sun. If you want time to the minute,
well just peek at anyone's watch for free. Ah, you want time
to the second; you might need to own a very good wrist
watch, a cell phone, or computer, or a WWVB RC clock.
Still not good enough? Expect to pay more for milliseconds.
Even more for microseconds; a GPS time/frequency receiver
perhaps. Nanoseconds? That's the realm of a cesium clock.

Those of us that really get into the hobby realize that "time"
is money: each digit of accuracy costs you another digit of
budget.

/tvb
http://www.LeapSecond.com


----- Original Message ----- 
From: "Jack Hudler" <jack at hudler.org>
To: <time-nuts at febo.com>
Sent: Friday, March 16, 2007 09:26
Subject: [time-nuts] Question for the cesium nuts.


> It seems to me that like all good things they must come to and end.
> 
> If all CBTs have a life expectancy that varies depending on the
> manufacturer.
> 
> What are we going to do when all the CBTs owned by amateurs start to end of
> life?
> 
> I for one am certainly not going to buy one, not at those prices! (Unless
> I'm retired then that's another story)
> You only have calculate the time value of money for that CBT purchase over
> the remaining time to retirement; If that doesn't stop you dead in your
> tracks then this group really is aptly named! :)
> 
> >From my perspective, that of wanting to own a Cesium Standard; I don't
> really want to layout the monies for something that's going to end of life
> on me shortly (few years) afterwards.
> 
> I know that handling (Caesium) Cesium-133 is tricky at best. It's a heavy
> alkali metal and contact with moisture is right out! 
> Other than that it's not terribly difficult to create a safe environment to
> work with it.
> 
> So there must be something else that's considerably more difficult than
> opening the tube, recharging the ampoule, resealing it, pulling an ultra
> high vacuum and baking it out.
> 
> I've not seen any pictures of a naked CBT, still I'm not too worried about
> cracking the tube open if its Pyrex, unless resealing it caused the cesium
> beam collimation to be lost.
> 
> Are there if any getters to worry about? If so, how would one ablate the
> contaminates of the surface?
> 
> Anyone care to start a discussion on the merits of restoring a CBT to life?
> 
> Jack





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