Saturday, September 6, 2014

Stepping Back Up With Classes: Lab Book 2014_09_06

Summary: Classes started this week.  They're a lot of fun, but they take time.  Consequently, the lab work is moving a little more slowly.  I'm looking into what we can accomplish with a YBCO superconductor sample.  The advantage is that we can test our experimental techniques using relatively cheap liquid nitroogen intead of iquid helium.  The downside is that with the size of YBCO sample we have, the expected maximum energy is only 3 deV which is kind of low without a specialized detector.

For more background on the experiment, please scroll to the bottom of the post.

The percolator peak does not appear when the detector is initially turned on.  The attenuator does however appear to create a rather copious amount of noise.

Suppose we used YBCO as a sample.  The energy we could expect doing a back of the napkin calculation is 3.8 keV.  The flux is approximately 230 photons for our sample size.  For a 25 square mm detector that may be available, this gives a total flux of 57 particles if we’re only 0.5 cm away.  This may work.

Another step would be to cycle the permanent magnet at a few Hertz to quench the superconductor repeatedly and increase the total flux.  The inside of the power supply control box is shown below.


The two potentiometers that control the supply are shown in the table below.  The coarse control is on the left and the fine control is on the right.

One technique might be to replace these potentiometers with a voltage controlled resistor.  The control circuit is shown below.



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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