Thursday, August 14, 2014

Calibrating Channels on the NaI Detector: Lab Book 2014_08_14

Lab Book 2014_08_14     Hamilton Carter

Summary:  Took several more spectra trying to characterize the behavior of the detector.

New to the experiment?  Scroll to the bottom for background.

Low Gain linearity run

Bias
1100 V
Gate Wind0ow
0.5 uS
Threshold
1.5mV
Attenuation
6 dB
Data set
HBC_0005
Source
Cs 137 taped to window
Start Time
8:58 AM
Stop Time
11:02 AM
Date
2014_08_14
x-y scope V/div
1, 0.5
Shielded?
Yes
Tube
Harshaw B-

The source is taped directcly to the window of the detector.  This will give the maximum number of particles from the source impacting the detector.  The counts from these runs will be used to determine the number of counts per second from the source.



Picture of the spectrum


This spectrum had to be patched to account for the overflow in the 662 peak channels as can be seen above.  The patched spectrum is shown below.


The slope voltage per channel was calculated again.  The results are shown below

channel
Count
Voltage
107
5633
184000
266
9656
662000




rise
478000

run
159

slope
3006.289

offset
-137673




107 test
184000




plateaue test
207.7887

In this case, the Compton edge energy that was used for the ‘plateau test’ was 478 keV as reported at http://nsspi.tamu.edu/media/141586/cs-137%20spectra.jpg

Yesterday’s troublesome question has become even stranger… maybe.  The original run that had a higher count on the K line was done at the same bias.  The only difference is that there was no shielding present.  Consequenlty, we have from the 12th with no shielding:


Notice that the K line is almost as tall as the 662 keV line.  On the 13th, with shielding we have:

Here’s another hint.  On the 12th, the source was not taped to the window.  This should account for the difference in counts in the 662 keV peak shown below for the shielded run on the 13th


There are several things to take note of in the above.  First, the counts for the source are increased.  This would be expected because of the source placement as mentioned above.  Second, notice that the plateau signal isn’t reduced by much.  This is an indicator that its noise, as suspected.  We still don’t have an answer for why the k line count goes down relative to the 662 keV line however.




Run from Dewar Source Distance
Bias
1400 V
Gate Wind0ow
0.5 uS
Threshold
1.5mV
Attenuation
6 dB
Data set
HBC_0005
Source
Cs 137 Placed 2 9/16” from center of window to center of source.
Start Time
1:32 PM
Stop Time
2:34 PM
Date
2014_08_14
x-y scope V/div
1, 0.5
Shielded?
Yes
Tube
Harshaw B-


Is there a different 32 keV peak here?  I thought I had eliminated the pedestal, but looking at the entire spectrum, the pedestal and what might be two peaks show up.


Analysis of the ‘new’ 32 keV peak
By blowing up the y axis on yesterday’s data, the ‘new’ peak at near 150 on today’s data can be seen near 140.  This roughly corresponds with the observed peak at 150 today.  Here’s the plot


It can be seen that neither peak gives a line equation that correctly predicts the Compton plateau edge

Choosing a 32 keV peak
channel
Count
Voltage
channel
Count
Voltage
86
5633
32000
150
5633
32000
995
9656
662000
995
9656
662000







rise
630000

rise
630000

run
909

run
845

slope
693.0693

slope
745.5621

offset
-27604

offset
-79834.3







150 test
76356.44

150 test
32000







plateaue test
742.5

plateaue test
760.2778

Here’s the same plat as above, from the Dewar distance source test that shows the two predicted Compton edge channels.  They’re both too large.


A Co 60 run was taken in hopes of making use of the 75 keV Pb X-ray.
Bias
1400 V
Gate Wind0ow
0.5 uS
Threshold
1.5mV
Attenuation
6 dB
Data set
HBC_0007
Source
Co 60 Taped to window
Start Time
3:07 PM
Stop Time
3:50 PM
Date
2014_08_14
x-y scope V/div
1, 0.5
Shielded?
Yes
Tube
Harshaw B-

Picture of spectrum


It’s debatable whether or not the 75 keV peak can be seen above or not.  The spectrum looks identical to the background only spectrum.  I’m running an overnight spectrum to get a cleaner signal.
Co 60 specctrum:


Background spectrum


The 75 keV peak in Co 60 can be seen in this spectrum




 *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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