[time-nuts] Mercury Ion Clock

Bob Camp kb8tq at n1k.org
Sat Nov 1 16:43:58 EDT 2014


Hi

> On Nov 1, 2014, at 2:35 PM, Jim Lux <jimlux at earthlink.net> wrote:
> 
> On 11/1/14, 11:05 AM, Magnus Danielson wrote:
>> Jim,
>> 
>>> However, if you were happy with "lab grade" construction, and you have
>>> the Kurt Lesker and Duniway catalogs as bedside reading, I think you'd
>>> have a chance.
>> 
>> Yes. I guess a bit of baking out the build is also to be recommended.
>> I guess most of us don't do vacuum in our labs, so there is a challenge
>> in itself, as there is many beginners mistakes to be done there.
> 
> 
> I haven't done high vacuum in quite a few years, but it is fascinating and frustrating. These days, quite a bit of surplus gear is out there that does make life easier (e.g. turbo molecular pumps).  A Hg Ion system isn't real huge, and doesn't have a big gas load, so a straightforward LN2 sorption pump would probably work as a batch mode(e.g. a bunch of the right material, plunged into a LN bath, and it the gas molecules just stick right to the material.. )
> 
> 
>> 
>>> The ion trap and such is a fairly straightforward thing, from what I
>>> understand: you need the usual vacuum pumps and such to build one.  If
>>> you don't want it to run for years without servicing, then issues of the
>>> mercury content are less important.
>>> (BTW, the space clock uses thermal dissociation of HgO to get the
>>> mercury)
>> 
>> Have tou cared to get the right isotope or do you use the natural
>> abundance spreading? Hg-199 has an abundance of 16,87%.
> 
> Interesting, I don't know if they go out and sort it, or if they set up the system so that it's basically a mass spec, and the wrong isotope doesn't make it through the quadrupole filter.

Don’t in any way discount the amount of effort in getting that filter to work “right”.

>   I'll bet the latter. No matter how good your offline enrichment process is, there will always be some other "stuff" in there.   For all I know, the actual ion trap is specific to the mass of the ions.
> 
> 
> 
>> 
>>> The PMT is an off the shelf thing. Check out the amateur built fusion
>>> reactor (fusor) websites on where to get PMTs and amplifiers (they're
>>> used behind a scintillator)
>> 
>> Ah yes. Got a NaI(Tl) scintilator with about 1 cm copper filter and a
>> matching PMT. No amp thought, but then again, I do not know what I
>> should measure with it. :)
> 
> You can measure radiation from common household objects like bananas
> 
>> 
>>> The 40 GHz stuff these days is not nearly as exotic as it used to be.
>>> The challenge might be test equipment when you're debugging your 40 GHz
>>> synthesis chain.
>> 
>> I was thinking the same, especially when consider optical clocks, then
>> 40 GHz isn't as esoteric.

Can you get this all done with 40 GHz as your “top” frequency?

>> Traditional cesiums and rubidiums use a pair
>> of synthesized frequencies being then sent into a step-recover diode
>> inside a tuned cavity which then does the mixing and selects the right
>> combination.
> 
> Same scheme might work here. Next time I'm talking to one of the DSAC folks, I'll ask how they do the synthesis chain.
> 
>> 
>>> I don't think it would be *easy*, but I think doable, and nothing in the
>>> system is particularly expensive or that exotic.  It's sort of like
>>> telescope building.. The raw materials to make a 18" reflector telescope
>>> aren't all that expensive, nor is there some secret sauce: it's just
>>> time to grind the mirror (and recover from mistakes) and build the
>>> system.
>> 
>> Would be a fun project to do, things to be learned.
>> 
> 
> For when you get tired of counting femtoseconds..

Then you need to build a second one to check the first one with.

Bob
> 
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