Summary:
Spent the day characterizing the NaI detector. The cool bit is that the 32 keV peak from
Cs137 is visible in the spectrum. It was
distinguished from the background and the pedestal by subtracting a background
spectrum from a spectrum with the source.
With the background subtracted out, the peak was clearly visible. This is important because while the maximum
predicted x-ray energy from the experiment is in the range of 150 keV, the radiation
may be over a spectrum that contains lower energies. The smaller the energy we can detect, the
better.
It looks like the detector signal may not be linear with the
PMT running at the high gain necessary to resolve the 32 keV peak. This isn’t entirely unexpected. Tomorrow lower gain tests will be run to see
if the detector is any more linear at lower gains. Linearity in this case means can the
calculated voltage per channel on the detector predict where other peaks in the
spectrum are. For more on this, read the entire entry, and stay
tuned for a separate post on the basics of the detector and the PMT .
If you’re new to the experiment, then scroll to the bottom
for all the background..
Background run 9:10 AM.
Bias
|
1400 V
|
Gate Wind0ow
|
0.5 uS
|
Threshold
|
1.5mV
|
Attenuation
|
6 dB
|
Data set
|
HBC_0002
|
Source
|
Background
|
Start Time
|
9:10 AM
|
Stop Time
|
9:41
|
Date
|
2014_08_13
|
x-y scope V/div
|
1, 0.5
|
Shielded?
|
No
|
Tube/Detector
|
Harshaw B-
|
Notes: The QVT
display/printer has to be bumped to print the first few channels. I’m not sure if there’s a data inaccuracy to
accompany this behavior or not. When the
start cursor is positioned at 0 and the print start button is pressed, the
printer only prints the first four channels.
By advancing the cursor one position at a time you can get the printer
to print additional channels. After
about three iterations of this process, the printer prints the rest of the data
in the capture range correctly. In the
first ten channels, there is one more channel printed than fits in the range
and there appear to be duplicates of the counts for two channels.
Spectrum picture:
Shielded Source Run
Bias
|
1400 V
|
Gate Wind0ow
|
0.5 uS
|
Threshold
|
1.5mV
|
Attenuation
|
6 dB
|
Data set
|
HBC_0003
|
Source
|
Cs 137
|
Start Time
|
9:59 AM
|
Stop Time
|
10:32 AM
|
Date
|
2014_08_13
|
x-y scope V/div
|
1, 0.5
|
Shielded?
|
Yes
|
Tube
|
Harshaw B-
|
Notes: Run HBC_0003
was done with the source taped directly to the center of the detector
window. The plan is to determine the
count rate from the detector using this data.
Spectrum picture
Shielded Background
Run
Bias
|
1400 V
|
Gate Wind0ow
|
0.5 uS
|
Threshold
|
1.5mV
|
Attenuation
|
6 dB
|
Data set
|
HBC_0004
|
Source
|
Background
|
Start Time
|
10:42 AM
|
Stop Time
|
|
Date
|
2014_08_13
|
x-y scope V/div
|
1, 0.5
|
Shielded?
|
Yes
|
Tube
|
Harshaw B-
|
Background Picture:
Source Signal minus Background from the previous two runs.
Made a few rough
estimates of the voltage per channel based on the assumption that the first
peak shown above is the 32 keV Barium K peak.
The first calculation was done assuming that every channel down to 0 had
useful information. It gave the
following results
channel
|
Count
|
Voltage
|
||||
80
|
5633
|
32000
|
400
|
|||
980
|
9656
|
662000
|
675.5102
|
|||
%error
|
||||||
29722.449
|
32 value on 662 V/channel
|
0.071173
|
||||
377600
|
662 value on 32 V/channel
|
0.429607
|
The second method assumed that all the channels were useless
below the pedestal peak of channel 36 and through them out. The results had less error:
Assume a pedastal at 36 and recalculate
|
||||||
pedestal
|
36
|
|||||
channel
|
Count
|
Voltage
|
||||
80
|
5633
|
32000
|
727.2727
|
|||
980
|
9656
|
662000
|
701.2712
|
|||
%error
|
||||||
30855.9322
|
32 value on 662 V/channel
|
0.035752
|
||||
686545.455
|
662 value on 32 V/channel
|
0.037078
|
Finally, the last method is probably the most correct one
and assumes the channels are linear and the peaks are at the correct locations. It just constructs V/channel as the slope of
a line between the two peaks.
rise
|
630000
|
run
|
900
|
V/channel
|
700
|
offset
|
-24000
|
pedestal voltage
|
25200
|
Barium K
|
32000
|
662 line
|
662000
|
Troublsome question of the day
Why does the 32 keV peak have fewer counts than the 622 keV
peak with the higher gain setting? Can
this be reproduced? Keep an eye on this
during tomorrow’s low gain linearity test.
$channel = \dfrac{energy-offset}{V/channel}$
The values for the two edges of the Compton plateau were
calculated using the last slope and offset determined above. The equation was
The results indicate that the gain may not be linear at the
current settings.
Compton peak
|
291.4285714
|
Compton Plateau
|
720
|
The measured channel values were about 311 and 658
respectively.
Expected plateau energies were pulled from http://www.spectrumtechniques.com/PDF/Compton%20Scattering%20Experiment%20by%20Prutchi.pdf
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.
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.
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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