A Prototype Diamond Detector for the Compton Polarimeter in Jefferson lab, Hall C

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A Prototype Diamond Detector for the Compton
Polarimeter in Jefferson lab, Hall C
Medium Energy Physics Group http//ra.msstate.edu/
dd285/mep.html
Amrendra Narayan Mississippi State University
JLab, Hall C, Compton Polarimeter Collaboration
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Outline

• The Compton Polarimeter
• Diamond as a Detector
• Electronic Setup
• Preliminary Results
• Future Tasks

Thanks Few Slides adapted from the talk of Roger
Carlini
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The Compton Polarimeter
A high precision Compton Polarimeter is under
construction at Hall-C for a non-destructive
continuous monitoring of the e- beam polarization
during the Qweak experiment and all other
polarized e- scattering experiments to follow
after the upgrade to 12 GeV capacity.
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Diamond A Closer look
Silicon is a typical choice for a multi-strip
position sensitive electron detector
Advantages lower leakage current, faster, lower
noise and rad. hard
Disadvantages smaller signal 40 smaller
Thanks Dr. R. Wallny (UCLA)
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The Diamond Detector

• Diamond is known for its radiation hardness
• We chose Diamond (artificially grown by Chemical
  Vapor Deposition) for the detector

How does it work?

• Operation of Diamond Detectors
• Bias voltage 1000 V,
• Charge collection distance 250m

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A Prototype Diamond Detector

• 10x10 mm2
• 500 µm thick
• 15 strips 450 µm wide

Metallization, Lithography wire bonding done in
High Energy Physics Lab at Ohio State University.
Thanks Prof. Harris Kagan and his group at OSU.
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Schematic of the Electronic Setup
Timing signal created only for signals gt
V_threshold
Analog to Digital Converter Histograming of the
digital signal
Charge pulse converted to a voltage signal and
amplified
The raw signal, a charge pulse
Signals accepted only in co-incidence with the
signal from timing filter amp
Timing Filter Amp
Ortec 928
Pre- amp
Linear Gate
MCA
Electron detector
Discriminator
Ortec 926
MPR - 16
STM 16
The signal is shaped (tail truncated) to avoid
overlapping of signals coming one after the other.
Shaping Amp
Visual display
counts
Channel number
A typical display
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Spectrum obtained by the Diamond detector
Threshold Voltage was low 50 mV
Shaping Amplifier _at_20 gain
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pedestal suppressed  spectra from diamond
threshold set to 150 mV to suppress the background
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Triggering with a Scintillator
Measuring only the minimum ionizing particles.
Only those beta particles would be detected which
pass the detector and reach the Scintillator.
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Schematic of the Electronic Setup
Analog to Digital Converter Histograming of the
digital signal
Charge pulse converted to a voltage signal and
amplified
The raw signal, a charge pulse
Signals accepted only in co-incidence with the
signal from Scintillator
Ortec 928
Pre- amp
Linear Gate
MCA
Electron detector
Discriminator
Ortec 926
MPR - 16
The signal is shaped (tail truncated) to avoid
overlapping of signals coming one after the other.
Shaping Amp
Visual display
counts
Channel number
A typical display
Instead of Self-trigger, we are now triggering
with the Scintillator
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Calibrating MCA
For Silicon dE/dx 1.664 MeV/(g/cm2) ?
2.33 g/cm3 Energy per e-h pair 3.6 eV
Thickness of the Si detector 300 µm
The mean Energy deposited then comes out to be
116.31 keV
Corresponds to
32310 e-h pairs
From particle physics data book
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Triggering with a Scintillator
Only those beta particles would be detected which
pass the detector and reach the Scintillator.
Measuring only the minimum ionizing particles.
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Response of the Diamond Detector
For Diamond ? 3.5 g/cm3 Z/A 0.499
Energy per unit e-h pair 13 eV
Positive bias
Counts
The Mean of 852 MeV
Channel
With the calibration by Si Corresponds to
Mean 708
4742 e-h pairs (expect 9000 e- for 220 µm CCD)
Negative bias
A 220 µm CCD was measured for this diamond with
a metalized dot
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Next Steps

• Repeat the measurements in a real electron beam
• (Detector has been shipped to TRIUMF, tests
  scheduled for mid-June)
• Build the full size Diamond Detector
• (4 planes, 21 x 21 mm2, 200mm pitch)
• An order for 4 planes placed with E6, delivery
  expected in 2 weeks.
• Quotes obtained from an E6 Spin-off to do
  metallization, the same company has expressed
  interest in making the carrier plates and doing
  the wire-bonding (turn key detector).
• Build the read-out electronics
• Build the DAQ
• Mississippi State Univ., Univ. of Winnipeg,
  Univ. of Manitoba, TRIUMF

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THANK YOU