Sunday, January 18, 2015

Experimental Estimates and Deconstruction: Lab Book 2015_01_16


Took apart the apparatus at the bottom of the proposed Dewar stick.  This is stick that will eventually support all the required apparatus in liquid helium.  Pictures follow.  Per normal, if this is your first day on the site, scroll to the bottom for the experimental background.



The inside of the Dewar measure out at 1 and 1/8 inches.  That works out to about 1.25 cm.  Then, plugging that into an expression for the size of cylinder we can get to fit


Working with square cylinders
Inscribe a square inside a circle
circle radius
0.5625
1.42875
cm
square side
0.795495129
1.010279
cm
Square radius
1.010278814

The above distances are to the wall of the Dewar.  If we back off of this a little bit and give ourselves  an 1/8 of an inch clearance at all the corners, we get
Working with square cylinders
Inscribe a square inside a circle
circle radius
0.5
1.27
cm
square side
0.707106781
0.898026
cm
Square radius
0.898025612

a radius of 0.89 cm.  That gives a maximum energy of about 290 keV and a total flux of 10,000 events per quench.  How does this jive with the sensitivity of the NaI detector?  This fits well within the range of the signals the detector is sensitive to:
Source
Peak Channel
Energy eV
Cd109


am241
110
26344
Cs 137
121
32000
Am241
221
59541
Cd109


Cs 137
2118
662000

For reference, here’s what the Cs137 spectrum looked like in the fiberglass Dewar

As it turns out, the brass disc at the bottom of the stick is too wide to fit in the Dewar.  It will b removed soon.

To Do: 
·         Characterize the detector response with the glass Dewar
·         Calculate the solid angle with the detector much closer to the source
·         Characterize the background response in the basement
Updates for the experimental plan:
Attempt to do a 90 degree rotation of the sample between runs.  This should help to account for any directionality issues due to the sample being a cylinder and not a sphere.

A possible source for the sample

Back to spheres?
The extruded version of this might work fine


Background
Hirsch's theory of hole superconductivity proposes a new BCS-compatible model of Cooper pair formation when superconducting materials phase transition from their normal to their superconducting state[1].  One of the experimentally verifiable predictions of his theory is that when a superconductor rapidly transitions, (quenches), back to its normal state, it will emit x-rays, (colloquially referred to here as H-rays because it's Hirsch's theory).

A superconductor can be rapidly transitioned back to its normal state by placing it in a strong magnetic field.  My experiment will look for H-rays emitted by both a Pb and a YBCO superconductor when it is quenched by a strong magnetic field.
This series of articles chronicles both the experimental lab work and the theory work that’s going into completing the experiment.

The lab book entries in this series detail the preparation and execution of this experiment… mostly.  I also have a few theory projects involving special relativity and quantum field theory.  Occasionally, they appear in these pages.

Call for Input
If you have any ideas, questions, or comments, they're very welcome!

References
1.  Hirsch, J. E., “Pair production and ionizing radiation from superconductors”, http://arxiv.org/abs/cond-mat/0508529

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