SiPM Evaluation Kit Quick Start Guide
SiPM
Eval Kit
4.2 Coincidence Time Resolution
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Two Evaluation Kits are mounted facing each other
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Note:
Two M6 mounting bolts are supplied for alignment when ordering two Evaluation Kits, they are screwed
to one of the Evaluation Kits, the second Evaluation Kit is slid on the mounting bolts
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This example uses two PM3350, each equipped with 3.0 x 3.0 x 5.0 mm³ LYSO with a ²²Na source placed
exactly in between the SiPMs
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Note:
²²Na has two decay branches. It emits two 511 keV annihilation γ rays in opposing directions, originating
from a β+ decay. The second decay emits a single 1.27 MeV γ ray. Of interest here are the two 511 keV γ rays for
the coincidence measurement.
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Monitor outputs are connected to a coincidence logic, e.g. realized by the oscilloscope
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Lower threshold of the coincidence logic defines the lower energy cut-off. The thresholds for both
Monitor outputs are set to the minimum between Compton edge and 511 keV photopeak to filter
for the energy respectively coincident events.
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The Coincidence Timing can then be measured by the time difference of both Amplified Signals. The
output of the coincidence logic triggers the measurement of the timestamps of both Amplified Signals.
•
Note:
Best timinig is achieved with a timing measurement close to the baseline. Typically with LYSO the opti
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mum is around 2 - 3 pe.
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The time stamps of both Amplified Signals can be measured e.g. with a leading edge discriminator,
a constant fraction discriminator or using an oscilloscope.
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The time difference between both time stamps is then histogrammed as shown in figure 4. The Coinci
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dence Time Resolution is the FWHM of the Gaussian distribution.
Fig. 4 Example of a CTR Histogram
Measured with two PM3350 at 4 V overvoltage, ²²Na source and LYSO 3.0 x 3.0 x 5.0 mm³
0
500
1000
1500
2000
2500
-1
-0.5
0
0.5
1
Time Difference [ns]
Coun
ts [a.u.]
CTR
180 ps FWHM
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