[Polhe3] Convection Cell Items

[Zhiwen Zhao]

Hi, AL

Thanks a lot for the detailed explanation.
I think we are ready to make a purchase order as your drawing, aren't we?

Zhiwen

On 05/25/2011 05:10 PM, William A. Tobias wrote:
>
> Hello Zhiwen:
>
> Quick answers to your questions:
>
> Scott used 1-inch spherical cells in his research.
>
> As for the bulb, some of the motivations:
>   a) to provide for more volume than the transfer tube alone: keep in mind
> that a TT cylinder with 6mm I.D. is much less volume then a sphere with
> 22mm I.D.
>   b) allow for doing "Spin Echo" measurements: for various reasons, a spin
> echo may allow one to more consistently measure the NMR amplitude for
> polarization. For example, in cases where the FID signal is too short
> (decays too quickly due to field inhomogeneities ie. short T2*) it becomes
> difficult to fit the FID back to time zero to extract an amplitude. This
> is especially true when there is much RF "ring down" from the initial
> pulse that contaminates the beginning of the FID. The solution is to do a
> spin echo in which case one just measures the peak of the echo. To do a
> spin echo successfully, you want most of your gas in a region of good
> RF (H1) field homogeneity since the pulses used in a spin echo are
> important to flip the 3He spins properly. Gordon's idea is to use a
> solenoid twice the length of the bulb so most of the gas lies well inside
> a homogeneous RF field during pnmr measurements, with minimal gas within
> the TT and other edges of the solenoid where the field is less
> homogeneous.
>
> In a typical spin echo, one first applies a pulse that tips the spins as
> much as 90-deg, just enough to get a large signal. During this time, the
> spins dephase. After a time t, one applies a 180-deg (pi) pulse causing
> the spins to rephase an additional time t later to give the spin echo. We
> simply measure the amplitude of the echo.
>
> As for tube tolerance, I can specify an outer diameter on the drawing if
> you prefer. I spoke to Mike and asked him what he thinks the OD of the
> tube would be if I ask him to make an ID of 5 to 6mm. He said the OD would
> be about 8 to 9mm (ie. 1.5mm wall thickness).
>
> Hope this information helps ...
>
>   - AL
>
>
> _________________________________________________________________________
>
> Al Tobias                            Office: (434) 924-7681
> Department of Physics                  Home: (434) 984-5025
> University of Virginia                  Lab: (434) 982-2233
> P.O. Box 400714                         FAX: (434) 924-7909
> Charlottesville, VA 22904-4714       E-mail: wat4y at virginia.edu
> _________________________________________________________________________
>
>
> On Tue, 24 May 2011, Zhiwen Zhao wrote:
>
>> Hi, AL
>>
>> I briefly went through Scott thesis, but I couldn't find the cell shape
>> he used.
>> Is the transfer tube with bulb a total new design?
>> Does the past experience from Gordon show that pulse NMR performs on the
>> transfer tube not good enough due to limited volume?
>> As the bulb is not much wider than the transfer tube, I do know the
>> volume is well defined?
>> I am a little worried that a bulb will actually bring more complexity here.
>>
>> Another thing is we want to find out what is the tolerance when Mike
>> makes the tube. That information is crucial for the design of the new
>> bottom oven piece. Do you know about that?
>>
>> thanks
>>
>> Zhiwen