Thursday, July 24, 2014

Magnetic Pulse Simultation Lives, NaI Detector Still on Life Support: Lab Book 2014_07_24

Lab Book 2014_07_23     Hamilton Carter

Summary:
The NaI detector still isn't giving good results despite additional efforts to understand its operation and any possible problems.  Tomorrow, the base that provides voltage to the tube will be rebuilt.  The can crusher simulation code has produced its first correct looking current output results.  A pulsed mgnetic field from a can crusher will be used to quiench the superconducting Pb sample in the experiment  The cna crusheer simulation code is being used to model the magnetic fields that will be avilable.

If you're new to the experiment, scroll to the bottom for background.

The can crusher simulation code is alive!  I’m porting the original IDL code used in the AJP article[1] about the can crusher over to Sage.  The project is open source and is hosted on github[2].  The pulsed magnetic field from a can crusher apparatus like the one described in the article is going to provide the pulsed magnetic field required to quench the superconducting sample of Pb.  Here’s a look at the first current output in comparison to the current output reported in the article. 


The table below compares the parameters from the article to the parameters used in the first run of the can crusher port

Article
Port
Capacitance = 400 uF
Capacitance = 500 uF
Voltage = 3000
Voltage = 5000

NaI Detector:
One last attempt was made at getting reliable spectra from the detector.  The base was firmly seated and taped to the detector.  Just as a precautionary measure, all holes and seams were covered with black electrical tape in case there were any light leaks in the system. 


The waveforms from the PMT were observed and are sketeched below


The majority of signals were the ringing waveform shown in the top of the diagram.  Every two seconds or so, there was a pulse as shown in the bottom part of the sketch above.  These waveforms are associated with actual particle detections.
Based on the signal width shown in the waveforms, the gate width of the QVT was reduced from 400 ns to 10 ns.  While this did move the pedestal lower in the spectrum, it still did not result in a spectrum correlated to the Cs137 source that was near the detector. 
The latest and greatest hypothesis is that the base of the PMT is damaged.  This base provides the accelerating voltages used by the PMT to amplify the light signals from the NaI crystal.  Parts to construct a new base, (resistors, capacitors, and a socket), were located and a new base will be constructed tomorrow.
References:
DeSilva, A. W., Magnetically imploded soft drink can , American Journal of Physics, 62, 41-45 (1994)



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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