Tuesday, September 2, 2014

Testing the Scintillator Near the Magnetic Field: Lab Book 2014_09_01

Summary:  The x-ray detector will be very near a rather large pulsed magnetic field in the experiment.  Tests were run today to determine how the scintillator reacts, if at all to the field. There were no visually available indications that the detector had behaved differently at all.  There is one channel that has a consistently higher count when the data is analyzed, however, this doesn't appear to be statistically significant though.

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

Took a background spectrum with the Dewar in place.  The percolator peak was not present when the spectrum was started, but had appeared by the time the spectrum was finished.
Bias
1500 V
Gate Window
0.5 Us
Threshold
1.5mV
Attenuation
3 dB
Data set
HBC_00029
Source
background
Start Time
8:35 AM
Stop Time
12:43 PM
Date
2014_09_01
x-y scope V/div
1, 0.5
Shielded?
Yes
Tube
Harshaw B-

There are two hypothesis regarding the cause of the percolating peak.  One is that the attenuator has a time dependent flaw, the other is that the detector itself has a time dependent flaw, (perhaps running the tube for too long on maximum bias?)
The objective of the background spectrum was to make sure that a background peak could be distinguished from the Cs 137 peak by determining where each of them resides.
The first background peak resides at channel 113.  The second peak is at channel 289.  The complete peak map so far with the Dewar present and 3 dB of attenuation is
Source
Peak Channel
Count
Rate
Cd109


am241
110
3.526
Background
113
1.177
Cs 137
121
3.77
Am241
221
7.2717
Background
289
3.210
Cd109



Yet another Cd 109 spectrum will be taken with the Dewar in place for comparison to the background count rate. 

Pulsed Current Source Detector Testing
A five minute background spectrum was taken with the NaI detector located immediately next to the pulsing coil as shown below.  Arcing was occurring in the pulsed supply.  The exact location of the arcing has not been isolated yet.





No visually noticeable change in spectrum was observed.  The data will be compared with a spectrum without the pulsing supply firing.  It appears we’re in the clear with regard to x-rays from the switch firing.  The detector was sitting directly on top of the case holding the switch and no change in background was detected.
Bias
1500 V
Gate Window
0.5 Us
Threshold
1.5mV
Attenuation
3 dB
Data set
HBC_00030
Source
background
Start Time
2:10 PM
Stop Time
2:15 PM
Date
2014_09_01
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
3 dB
Data set
HBC_00031
Source
background
Start Time
2:22 PM
Stop Time
2:28 PM
Date
2014_09_01
x-y scope V/div
1, 0.5
Shielded?
Yes
Tube
Harshaw B-

There may be two points at channels 147 and 220 that are statistically significant in the following.  Retaking a pulsed spectrum over a shorter window to see if these peaks remain.



Bias
1400 V
Gate Window
0.5 Us
Threshold
1.5mV
Attenuation
3 dB
Data set
HBC_00032
Source
background
Start Time
29.7 seconds
Stop Time

Date
2014_09_01
x-y scope V/div
1, 0.5
Shielded?
Yes
Tube
Harshaw B-

Bias
1400 V
Gate Window
0.5 Us
Threshold
1.5mV
Attenuation
3 dB
Data set
HBC_00033
Source
background
Start Time
29.9 seconds
Stop Time

Date
2014_09_01
x-y scope V/div
1, 0.5
Shielded?
Yes
Tube
Harshaw B-


To rule out random background, two more runs will be taken with shorter sampling windows around the pulsed supply firing.  One run will be taken with a pulse firing.  The other will be taken with background only.  The results are shown below.
Bias
1400 V
Gate Window
0.5 Us
Threshold
1.5mV
Attenuation
3 dB
Data set
HBC_00034
Source
Pulsed once
Start Time
5.7 seconds
Stop Time

Date
2014_09_01
x-y scope V/div
1, 0.5
Shielded?
Yes
Tube
Harshaw B-

Bias
1400 V
Gate Window
0.5 Us
Threshold
1.5mV
Attenuation
3 dB
Data set
HBC_00035
Source
Background
Start Time
5.6 seconds
Stop Time

Date
2014_09_01
x-y scope V/div
1, 0.5
Shielded?
Yes
Tube
Harshaw B-

Is the following significant?


It’s unclear whether or not the increased count in the last few channels above is significant.
Here are the spectra with all the available data entered


There’s an outlier at channel 220 which is where the other outlier at channel 224 was recorded.
I checked for a difference in the overflow channel of the detector.  Here’s the available data so far:
Run
Overflow Channel
Adjusted to 5.7 second run
Duration
Poisson Uncertainty
VeryShortPulse
256
256
5.7
16
VeryShortNoPulse
239
243.2678571
5.6
15.45962
Difference
17
12.73214286

The difference in the counts from the overflow channel for the two runs is within the Poisson uncertainty.

Percolating Peak
The high count peak in the low channels range is still somewhat of a mystery.  It is probably not due to the detector/PMT combination however.  During one run today, I forgot to attach the input cable from the PMT to the QVT and recorded the following spectrum:



The peak has the following observed properties:
1.  The peak only appears when attenuation is not equal to 0
2.  The peak does not appear immediately after the detector has been turned on, but only after a greater than one minute delay, (I'm working on characterizing the delay).
3.  The peak moves in channel number to the right as attenuation is increased.  This is independent of which attenuator switches are activated.

Plans
The pulse data isn’t significant enough to warrant more runs at this time.  The detector will be located further away from the pulser switch during the actual experiment.
To Do:  Take similar data with the actual experimental setup.
The data taking today did highlight the need for an automated data acquisition system.  The system should have the following features:
1.  Read all channel data into a file automatically.
2.  Activate and deactivate the QVT sampling based on an external signal.


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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