Tuesday, August 19, 2014

Mapping the NaI Detector's Energy Response: Lab Book 2014_08_19


Summary:  The bias on the PMT was turned to its maximum safe value of 1500 V for maximum gain.  There is a bit of a voltage drop in the PMT base between supply voltage and the anode voltage, so at 1500 V supply voltage, we’re still not running at the maximum rated cathode to anode voltage of 1500 V.  Using peaks from several sources, a channel vs. energy graph was constructed.  Although some of the peaks have small counts and need to be measured more accurately, the linearity looks good with a resolution of about 188 V per channel and a maximum detectable energy of about 203 keV.

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

Data and Channel vs. Energy Mapping

Bias
1500 V
Gate Window
0.5 uS
Threshold
1.5mV
Attenuation
0 dB
Data set
HBC_00011
Source
Am 241 Taped to window
Start Time
~ 11:17 AM
Stop Time
~~ 1:30 PM
Date
2014_08_19
x-y scope V/div
1, 0.5
Shielded?
Yes
Tube
Harshaw B-

Spectrum Data





Bias
1500 V
Gate Window
0.5 uS
Threshold
1.5mV
Attenuation
0 dB
Data set
HBC_00012
Source
Cd 109 Taped to window
Start Time
2:18 PM
Stop Time
2:50 PM
Date
2014_08_19
x-y scope V/div
1, 0.5
Shielded?
Yes
Tube
Harshaw B-



Bias
1500 V
Gate Window
0.5 uS
Threshold
1.5mV
Attenuation
0 dB
Data set
HBC_00013
Source
Background
Start Time
2:56 PM
Stop Time
3:37 PM
Date
2014_08_19
x-y scope V/div
1, 0.5
Shielded?
Yes
Tube
Harshaw B-








Bias
1500 V
Gate Window
0.5 uS
Threshold
1.5mV
Attenuation
0 dB
Data set
HBC_00014
Source
Cs 137 Taped to window
Start Time
3:35 PM
Stop Time
3:59 PM
Date
2014_08_19
x-y scope V/div
1, 0.5
Shielded?
Yes
Tube
Harshaw B-

This run needs to be much longer to get more reliable statistics.  The run today was a short one to get a ballpark picture of the detector’s channel vs. energy behavior





Channel Mapping
Using the peaks location from the three sources listed above, Am 241, Cd 109, and Cs 137, the response of the detector with respect to energy was mapped out.
The data for the peak locations is shown in the table below
Source
Peak Channel
Energy eV
Cd109
55
22100
am241
86
26344
Cs 127
104
32000
Am241
262
59541
Cd109
406
88000

1023
203390.39

The last row is a calculation using the least squares regression fit parameters to determine the maximum energy that can be detected.
The peak energies vs. channel are shown in the following graph.


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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